Hart Cooley Tech Talk

December 2003 Introducing the Tech Talk Newsletter by Dave Fetters This is the first in a series of publications that will discuss topics of interest for all of our customers and potential customers. “Customers” include the family of employees within Hart & Cooley, as well as anyone with an interest in our products and services. Our aim is to emphasize education related to the HVAC industry. We will do this through the publication of our Tech Talk newsletter. As the name Tech Talk implies, we will present subjects of a technical nature, although we also may choose subjects that are not technical, but related. Every effort will be made to discuss topics in a way that is easy to understand. Your questions about the subject matter are welcome, as are suggestions for future topics. We encourage your participation. Feel free to comment about the effectiveness and depth of coverage of the subject matter. You may contact us through our web site at www.hartandcooley.com. From the home page, click on “Contact Us” and then “E-mail Customer Service.” From the home page you also can click on “Site Map” and then “Comment/Question Form.” You may contact me directly as well at [email protected]. Some of the 40-plus topics that we have listed and will eventually cover are:

Opposed-blade vs. multi-shutter dampers Louver performance and how to size them

What does “Throw” mean and how to use it

Repainting registers The information we need to help you size Type B gas vent

The information we need to help you size grilles, registers and diffusers

How to determine engineering data for sizes not shown in our catalog

The difference between flexible duct and flexible connectors

How we can help you deal with inspectors

Helping you understand codes and standards

Again, we want to assist you as much as we can, so please suggest topics that will help you with your work. You might consider placing copies of these bulletins in a convenient location for your employees and customers. We also encourage you to incorporate the topics of these bulletins within your own publications if appropriate.

January 2004 Type B Gas Vent Interconnection Fittings by Dave Fetters TT-02 Changes or additions to existing B vent systems sometimes require the installer to use new Hart & Cooley B vent with whatever brand is already in place. Appliance replacement, or building additions or modifications, may mandate adding more B vent to a system or changing what is in place. Since different brands of B vent have different locking designs and can produce different amounts of airspace between the inner and outer walls, a straightforward coupling of different brands is usually impossible. Although the inner diameters are universally the same nominal dimension, the outers may be different, preventing the necessary pipe overlap for a good connection. We wanted something other than a makeshift connection. We wanted a fitting that would allow the mixing of brands while providing a positive lock—a lock that meets Underwriters Laboratories Standard 441 for B vent. We wanted to prevent the use screws to hold the joint together, thus avoiding a potential source of noise. We wanted to be able to have other brands mate to our B vent at both the male and female ends.

We wanted to accommodate the most common sizes used. Hart & Cooley has UL-listed male and female interconnection adapters that meet these requirements. When speaking of these adapters, it is easy to confuse them. We speak of “male” adapters as those that adapt other brands to Hart & Cooley—“theirs-to-ours” in the direction of flue gas flow. So a male adapter will fit onto the male end of another brand heading away from the appliance. A “female” adapter, or “ours-to-theirs,” allows for the male end of Hart & Cooley pipe to adapt to the female end of another brand. Another way to remember which end is which is that flue gases flow into the female end and out the male end. We have an arrow on pipe that points toward the male end, showing the direction of flow of the flue gases. The chart on the reverse side of this newsletter, which appears in our Gas vent & chimney systems product catalog, lists the adapters that we offer. □

(continued on reverse side)

Hart & Cooley Adapter Model

Manufacturer

Pipe Diameter

Airspace

Male

Female

Metalbestos

3" - 6" 7" - 8"

1/4" 1/4"

RA or RPA RA

RRA –

Metal-Fab

3" - 6" 7" - 8"

1/4" 1/2"

RA or RPA RPA

RRA –

AmeriVent

3" - 6" 7" - 8"

1/4" 1/2"

RA or RPA RPA

RRA –

Air-Jet

3" - 8" 7" - 8"

3/8" 3/8"

RAA RAA

RRA –

DuraVent

3" - 8" 7" - 8"

5/16" 5/16"

RAA RAA

RRA –

RAA Male Adapter adapts other brands of B vent

to Hart & Cooley vent

RA Male Adapter adapts other brands of B vent

to Hart & Cooley vent

RRA Female Adapteradapts Hart & Cooley vent to

other brands of B vent

TT-03 March 2004 The Difference Between Flexible Air Ducts and Flexible Air Connectors by Dave Fetters Flexible air ducts and flexible air connectors share many of the same traits, yet are different enough that they are uniquely separate products. All of the national codes share similar language, as represented by the International Mechanical Code, 2003 edition (paraphrased):

Flexible air ducts and flexible air connectors, both metallic and nonmetallic, shall be tested in accordance with UL 181. Such ducts and connectors shall be listed and labeled as Class 0 or Class 1 flexible air ducts or flexible air connectors and shall be installed in accordance with the terms of their listing and the manufacturer’s installation instructions.

It goes on to say:

Flexible air ducts shall not be limited in length.

Flexible air connectors shall be limited in length to 14 feet. Flexible air connectors shall not pass through any wall, floor, or ceiling.

These last two entries define the primary difference between the two products. Air ducts must pass 15 UL tests, whereas connectors are not required to pass the flame penetration, puncture, or impact tests. All Hart & Cooley flexible ducts are insulated and have a rectangular label that shows the UL listing mark and clearly states that it is an air duct. Hart & Cooley flexible connectors have no insulation, but have a round label with the UL listing mark, the words “air connector,” and the words “For installation in length not over 14 ft.”


If flexible connector is used in an application, the 14-foot maximum installed length limit may not be increased by installing a splice at the end of a 14-foot length of connector. If a listed connector is used in an application that does not require the use of listed connectors, it could still be subject to the 14-foot length limitation. Whether or not Hart & Cooley-listed air connector may be used for bathroom or dryer vent is a common question. Subject to the 14-foot limitation stated above, our air connectors—whether listed or not, whether polyester or corrugated aluminum—may be used, provided the appliance manufacturer allows for its use in their installation instructions.

TT-04 April 2004 Spiral Diffuser Scoop Used as a Balancing Device by Dave Fetters Hart & Cooley’s extruded aluminum spiral duct diffusers are available with

an optional “scoop” air deflector, which helps funnel air flowing along the duct

to exit at the diffuser. Without the scoop, depending on the system design,

air having momentum along the duct may be reluctant to exit at the desired

diffuser location or in the optimum amount.

The scoop length is about 45% of the

diffuser width (the dimension along the axis of the duct). It does not cover the

full opening of the diffuser core area and, therefore, will not act as a volume-

control damper with full shutoff capability. We did not want the scoop

to be so long that it could easily reach the opposite side of the duct and

disrupt downstream flow.

The 2000 International Mechanical Code states: “Balancing dampers

or other means of supply air adjustment (my underline) shall be provided in the

branch ducts or at each individual duct register, grille, or diffuser.” Our scoop

is not a damper in the traditional sense. However, the code clearly says “or

other means,” so an add-on duct damper, an air-control grid, an air

diverter, a flexiturn, or the spiral diffuser scoop would all comply as

supply air adjustment means. Nowhere does the code imply that one needs

100% shutoff capability, only that air adjustment be provided. This

requirement only applies to branch ducts. Main ducts do not have to meet

this requirement.

TT-05 May 2004 Throw, Blow, Flow, Oh No! by Dave Fetters

Everyone has thrown a ball of some kind in their lifetime, and we generally pay attention to how far it traveled as a measure of our strength, accuracy, or overall abilities. We can see the result of our effort. Similarly, when air flows out of a supply register, we’d like to know the result. Since we cannot see what is happening (although we might be able to feel it), we use throw as one indicator of a register’s abilities. Throw is a measure of how far the supply air stream is blown into the room. Throw is measured in feet from the face of the register along the primary direction of flow. However, a throw distance is meaningless unless given a point of reference. By that I mean, “What is the air doing at the end of the designated throw?” Is it successfully mixing with room air to make the occupied space comfort-able? To be mixing it has to be moving, but how fast?

We use the term terminal velocity in conjunction with throw to describe what the air is doing at the end (or terminus) of the designated throw. A typical terminal velocity is 75 feet per minute (FPM). This means that no matter how fast the air is blown out of the register, the throw tells us, at that distance, that the air has slowed to 75 FPM. The supply air velocity measured at the register face determines how far the throw will be. The faster the air exits the face, the farther the air will travel into the room. The resistance of room air to the supplied air will cause the supply air to slow down. Eventually, the supply air will slow enough to become ineffective in mixing with room air. The point that air velocity becomes ineffective is called the terminal velocity. It is somewhat arbitrary, but generally ranges from 150 down to 50 FPM.


©2004 Hart & Cooley, Inc. All rights reserved


The distance from the face to where this terminal velocity occurs is the throw. Example: The engineering data for a sidewall supply register states that all throws are at a terminal velocity of 100 FPM. No matter what the face velocity is or how much air is being delivered, each throw is measured at the point where the supply air stream has slowed down to 100 FPM. If we would have used 75 FPM as the terminal velocity, the throws would have all been longer (farther from the face). At the register face where the throw is “0,” the velocity of the supplied air is highest. No matter what distance we choose to stop moving away from the face, there will always be a corresponding velocity that becomes less and less the farther away we move.

Always look for the stated terminal velocity in the engineering data when discussing throws. Terminal velocities will change depending on the type of product and the intended use. We may even show two or three throws for the same size product corresponding to different terminal velocities. As always, if you have questions, call us toll-free at 800.433.6341, check out our web site at www.hartandcooley.com, or send us an e-mail at [email protected].



TT-06 July 2004 Noise Criteria (NC) – Part 1 by Dave Fetters

The selection of grilles, registers, or diffusers (GRDs) can sometimes be influenced by noise generated by airflow passing through the device. Many applications require a quiet environment where the designer wants to limit, or not add to, the background noise level by carefully choosing the air delivery product. Movie and recording studios, sound stages, libraries, concert halls, executive boardrooms, and churches all require attention to the noise criteria (abbreviated as NC) for GRDs. NC is a single-number designation that gives us a comparable reference of how loud a register will be at a certain CFM delivery. Usually, a single NC number is assigned to a particular style and size of a register at a fixed airflow rate. Any change in the size or style of GRD, as well as to the airflow rate, will affect the NC rating. The NC number is a simplified approach to acoustics—the study of sound. The terminology and

technology used to measure sound is cumbersome for those of us who don’t work with it on a regular basis. Therefore, NC was conceived to provide uncomplicated information to meet acoustic design goals without having to resort to sound consultants. It is not, however, a perfect number for giving us a total picture of the acoustic environment. For instance, NC does not tell us anything about the frequency at which the “loudest” sound occurred. Except for rooms where sound intensity and sound quality are critical to the occupancy, NC is adequate for the majority of HVAC work. The velocity of the air passing through the various styles of faces influences sound levels attributed to GRDs. Additional influence on potential sound is determined by whether dampers are installed or not, the damper settings, the blade deflection settings, and GRD


location. But the biggest influence is the air velocity. As velocity increases, the noise criteria will likely increase at a faster rate. Doubling the velocity can more than double the NC rating. Sometimes, system noise is unfairly blamed on the register. System noise of rumble, hiss, whistle, whine, and vibration are generated by pumps, fans, compressors, combustion, motors, and turbulent airflow in poorly designed ductwork, and this noise is conducted by ductwork and/or radiated from the system. A quick check of whether the register is contributing to the overall noise spectrum can be made by removing it from its mounting location while the system is operating and comparing the sound levels. Many of Hart & Cooley’s GRDs have NC ratings in the engineering data tables. For those products that do not have NC, there is a table in our catalog and on our web site of recommended maximum velocities that should be considered to ensure low noise based on occupancies. Next month we will continue with Part II of this discussion.


TT-07 August 2004 Noise Criteria (NC) – Part 2 by Dave Fetters

As we indicated last month, grille, register, or diffuser (GRD) selection and sizing are often influenced by the potential noise the product is likely to make when air is flowing through it. Noise and Sound: We need to be careful about terms and definitions here. The word noise and the word sound are often and incorrectly used as one and the same. Noise is an undesired sound. Noise is erratic, intermittent, or random, and interferes with normal room activity. Sound, on the other hand, is perceived or “heard” as comfortable, wanted, or at least not annoying, not too loud, and relatively constant as it blends into the background and/or has pleasing qualities to it. Sound is noise if it is too loud, unexpected, annoying, uncontrolled, occurs at the wrong time, or is unpleasant—you get the picture. One person’s loud stereo system is “wanted sound” to him, but to his neighbor at bedtime it is unwanted, undesired, too loud, and therefore noise. Noise is usually (but not always) inclusive of most frequencies at the same time. Frequency (tone or pitch) is a method of categorizing sound. Low frequency sounds rumble, even vibrate or rattle, like thunder. High

frequency sounds include hiss, whine or buzz. Examples of pleasant sounds are wind chimes or stereo music that is soothing, water lapping against a sailboat hull, or a light breeze rustling leaves in a tree. A motorcycle has a satisfying “sound” to its rider. Boisterous conversation is an enjoyable sound to the participants, but may be unwanted noise to someone seated nearby. A crying newborn is probably a satisfying sound (and a relief) to the mother, while to the uninterested, noise. The perception of sound is influenced by loudness (magnitude). A noise can be less harsh than a sound that is too loud. Niagara Falls is a loud noise of complex tones, but it’s enjoyable. The electronic hum of a poorly working computer is a sound of a simple tone that can be very annoying if the office is otherwise quiet. Orchestras can be very loud, but the music is anticipated and, therefore, a pleasant sound. Jet engines at close range are very loud and unpleasant. A mosquito buzz isn’t loud, but it is a noise that equates to an unpleasant experience.


How we perceive sound is also influenced by the frequency. Humans can stand louder sounds at low frequencies than at high frequencies. The duration or how long a sound lasts influences a person’s reactions to it as does how often it occurs. Unfortunately, it is hard to predict in any precise way peoples’ response to sound. It is part physiological and part psychological; it depends on the situation, and it depends on the individual. The NC number we use for our products is a simplified approach to acoustics—the study of sound. Our concern in the HVAC arena is to limit the background interference of whatever human activity is taking place. A noise criteria chart has been developed to show lines of “constant loudness” as the human ear would perceive it. The plot on the chart below is typical of a “sound room test” result we might see

from a particular register at a single airflow rate. The highest NC number generated is 30 determined by the highest penetration of octave band level into the curves. Even though it occurs at 1000 Hertz, the NC doesn’t tell us anything about the frequency. It only gives us an idea of the relative loudness. So even though we spend considerable time measuring sound in our reverbera-tion chamber at different airflows and frequencies for each size and model of product, the end result is still the single-number “NC.” NC does not address acoustical quality properties, such as whether the background noise generated by the register will be annoying (rumble, hiss, machinery noise, or vibrations), only whether the background noise will noticeably interfere with sounds people want to hear, such as speech.


TT-08 September 2004 Sizing a Register or Diffuser by Dave Fetters Conceptually, choosing a supply register or diffuser would seem to be straightforward, and most of the time it is. There are a number of influences that could affect the choice. Putting emphasis on one influence over the others will alter the outcome, but much depends on one’s priorities. It’s like pouring various ingredients into a blender and ending up with a flavored drink. Too much of one ingredient will dominate the taste. Some selection options for choosing a register will be more important than others, thus influencing the model and size.

Some of the possible input criteria for making a selection are:

CFM Face velocity Throw Pressure loss Noise criteria Mounting location Heating/cooling/both Looks

Availability Price Style Size limitation Material New/replacement

In practice, one’s experience, geographical location, and the type of occupancy or activity in the space under consideration may eliminate some variables, such as mounting location, heating or cooling or both, availability, style, and material like steel, aluminum, or even plastic. Ceiling Diffuser For this initial discussion of sizing a supply register or diffuser, we will narrow the selection criteria to only CFM, face velocity, and throw, which will minimize unnecessary complications. The location is a ceiling, and a circular or 4-way pattern is required. A circular ceiling diffuser, such as our #16, is one possible choice.


The chart below is the engineering data for Hart & Cooley’s #16 round ceiling diffuser. With a requirement of 120 CFM, there are a number of choices for a size that can deliver this airflow. A 6-inch diameter will deliver 120 CFM at a face velocity of 900 feet per minute (FPM) and a radial throw of 5 feet. An 8-inch will also deliver 120 CFM, but at a reduced face velocity (and quieter delivery) of about 530 FPM and a throw of approximately 4 feet. And lastly, a 10-inch will have a face velocity of 350 FPM and a throw of 3 feet. Given the three potential choices, think about throw as the next selec-tion criteria. The greatest throw comes with the highest face velocity, but don’t forget that the same high face velocity may cause some back-ground noise that might be bother-some if used in a library as opposed to a room with a higher level of activity. Increasing face velocity will intensify the pressure loss. (Doubling the velocity will quadruple the pressure loss!)

This simple table allows for a visual interpolation of data. A more precise method is to use the relationship:

CFM = Face Velocity x Area The “Area” (in square feet) for each size is the “Ak” number listed under each diameter. For instance, to find the face velocity of the 10-inch at our stated 120 CFM requirement, divide 120 by the Area: CFM ÷ Area = Face Velocity or 120 ÷ .345 = 348 FPM face velocity. Another ceiling diffuser to consider is the A504. This product is square and made of aluminum, providing an alternative when looks and material become selection criteria. I consider this example an “introduction” to sizing a supply diffuser. In future editions, we will study examples where we must choose the register or diffuser based on more stringent performance limitations, as well as examples that require narrowing a choice of product by prioritizing many of the selection criteria.

Engineering Data for 16 Round Ceiling Diffuser

Face Velocity 300 400 500 600 700 800 900 1000 Pressure Loss .006 .010 .016 .022 .031 .040 .050 .062 6" Ak .135

CFM Throw 55

2.5653.0

803.5

954.0

1054.5

120 5.0

1355.5

8" Ak .225

CFM Throw

70 2.0

903.0

1153.5

1354.5

1605.0

1805.5

200 6.5

2257.0

10" Ak .345

CFM Throw

105 2.5

1403.5

1754.5

2105.0

2406.0

2757.0

310 8.0

3458.5

12" Ak .500

CFM Throw

150 3.0

2004.0

2505.0

3006.0

3507.5

4008.5

450 9.0

50010.5

14" Ak .625

CFM Throw

190 3.5

2504.5

3155.5

3756.5

4408.0

5009.0

565 10.0

62511

18" Ak 1.04

CFM Throw

310 4.5

4156.0

5207.0

6258.5

73010.0

83011.5

935 13.0

104014.5

Terminal Velocity of 50 FPM


TT-09 October 2004 Return Grille Locations by Dave Fetters

Return grilles or filter grilles are just

as important to the HVAC system as

the supply side products. Return air

volume to the air handler must

equal the supply air volume pumped

out by the fan, or system

performance will suffer. Air will not

readily flow into a room from a

register unless there is a relief

opening for the “stale” air to flow

out. This could be as simple as

having the door open to a small

room for air to drift out to an

adjacent room that has a return

grille.

Door grilles, or “transfer grilles” as

they are sometimes called, allow

room air to flow out of the room if

the door is closed most of the time,

and otherwise doesn’t have its own

return grille. Bathrooms and

janitor’s closets in some commercial

buildings are examples.

A common misunderstanding is that

return grilles have a dramatic effect

on room air distribution. In fact the

opposite is true based on laboratory

research. Return airflow has a

negligible effect on room air patterns

because of its low-capture velocity.

This means that the sphere of

influence, or the area affected by the

return grille, is limited to a little

over one duct diameter away from

the face. Within this short distance,

the air is captured and pulled into

the grille. Outside this immediate

area, the capture velocity is so low


as to be ineffective in influencing

room air motion. Since the airflow

approaches the grille from all

directions, its velocity decreases

rapidly as the distance from the

opening increases. In other words, a

return grille will not “reach out into

the room” and pull the room air

toward itself.

There is a preferred location for

returns and that is in an area called

the “stagnant zone.” This is an area

in the room that is outside the

influence of the supply register

where room air motion is inactive

except for natural convection.

When heating is the primary

requirement, the stagnant area will

be close to the floor where the

coolest air will gather. Thus, the

coldest air will be delivered back to

the heating appliance.

If cooling is the priority, the

stagnant area will be the warm air

that gathers near the ceiling that

should be removed first and

returned to the cooling coils.

For a combination heating and

cooling system, the preferred

location for the returns will meet the

requirements of one of the seasons,

but will only be a compromise for

the other. The designer needs to

weigh whether heating or cooling is

more important and place returns

accordingly. Even though for the

remaining season the returns are not

ideally placed, the performance will

be more than adequate.

Return air face velocity depends

somewhat on the environment and

grille design. Stamped, louver-faced

residential returns like our 650 or

672 should be limited to about 600

feet per minute (FPM) as a rule of

thumb. Commercial “assembled”

returns can stand velocities up to

1000 FPM if the room background

noise allows. Filter returns that use

throw-away fiberglass disposable

filters should limit the face velocity

to 400 FPM. The maximum rating

for these types of filters is usually

500 FPM, beyond which their ability

to remove dirt from the air stream

diminishes rapidly.


TT-10 November 2004 Chimney Liner Applications and Limitations by Dave Fetters

Hart & Cooley manufactures an

aluminum, corrugated chimney liner

system that is Underwriters

Laboratories tested and listed. It

may only be used with natural or

propane gas-fired Category I

appliances listed for use with Type B

gas vent. This aluminum is the

same alloy and thickness as the liner

in our UL-listed B vent. This liner

system may not be used with liquid

(oil) or solid (wood or coal) fuel-

fired equipment.

Our UL listing allows the liner to be

installed in new or existing masonry

chimneys, as well as existing, but

unused, factory-built chimneys and

B vents. The liner may touch the

interior surfaces of these flues. An

incorrectly built masonry chimney

that does not have the required

two-inch airspace to combustibles

(direct contact instead) may also be

used with this liner without further

safety concerns because of lack of

airspace clearances.

When we introduced the chimney

liner product line several years ago,

we “required” that masonry

chimneys with at least one wall

exposed to the outdoors be relined

with Type B gas vent instead of

chimney liner. At the time, we were

being cautious, knowing that in

order to vent properly chimney

liners must heat up quickly and stay

warm. We felt that chimneys

exposed to cold air temperatures

may become too cold to work

properly, resulting in poor venting


and condensation within the liner.

However, after several years of

experience, we found that proper

venting is usually achieved with

liners in exposed masonry

chimneys. Therefore, although we

still “recommend” that Type B gas

vent be used in these instances, we

don’t “require” it. Insulating

chimney liners is another method

that helps assure proper venting.

Additional steps to help prevent

condensation are:

Proper sizing using the

dedicated sizing tables in our instructions, or the required 20% reduction in capacity if using B vent sizing tables.

Proper combustion air openings.

Venting with a draft hood-

equipped appliance.

Using as much B vent as possible to line the vertical portions of an exterior chimney.

As with any chimney or vent

product, follow our installation

instructions and the applicable

codes to ensure a safe and trouble-

free installation.


TT-11 January 2005 Information Required to Size B-Vent by Dave Fetters

We are often asked to size B-Vent

installations to address performance

issues with an existing vent system

and/or to satisfy the requirements of

the Fuel Gas Code. In order to

perform a thorough evaluation of the

vent system, which includes

compliance with the Fuel Gas Code,

we require some installation

specifics.

For a single-appliance vent system,

we need:

• The type of appliance—water

heater with draft hood,

mid-efficiency (80% or

fan-assisted combustion) furnace,

or boiler

• BTU input

• Special appliance configurations,

if any (motorized damper, 2-stage

firing, etc.)

• Vent height measured from the

appliance collar to the cap

• A description of any offsets

(angle and length between

elbows)

• Whether the connector is single-

wall or B-Vent

• Collar size is optional, but helpful

For a multiple-appliance (two or

more) vent system on the same

level, we need:

• The types of appliances (see

above)

• BTU input of each appliance


• Special appliance configurations

(see above)

• Common vent height measured

from the tallest appliance collar to

the cap

• Common vent offset angle and

distance between elbows

• The spacing between appliances

and their locations relative to the

vertical portion of the vent

• Whether the desire for connectors

and manifold is for single-wall or

B-Vent

• Rise and number of elbows for

each appliance connector

• Collar sizes are optional, but

helpful

A system sketch is very helpful and

provides a forum for notes and a

signature from a Hart & Cooley

engineer. Not having all the

information forces us to call for the

missing data, adding to the

turnaround time. Incomplete

information may limit our choices of

venting options.

A multi-story sizing request should

always include a sketch. Besides the

appliance types and inputs, the

appliance location dimensions must

include the horizontal distances of

all appliances on each floor from the

common vertical vent and the

relative locations of the

interconnection tees on each floor.

There are definitions and sizing

examples of single-appliance,

multiple-appliance, and multi-story

venting in our Gas vent, chimney

sizing & application guide. These

examples will help you understand

the information we require to size a

system properly. The sizing guide is

available from our web site at

www.hartandcooley.com.

You may contact us with B-Vent

sizing needs by telephone, mail, fax,

or by e-mail (through our web site).

Please include your name, phone

number and fax number on your

sketch.


air-volumecontrol damper

TT-12 February 2005 210 Floor Register/265 Grille by Dave Fetters

These companion products have been part of the Hart & Cooley product line since 1947! Many other products have come and gone, but these have endured. The Model 210 floor register is the one with the air-volume control damper attached. The Model 265 is a grille, or “face only,” and has no damper.

Part of the explanation for their longevity is due to the robust construction. There are not many products these days that haven’t undergone some kind of cost-reduction program, with one end result being the use of thinner steel. There is a continuing need for floor registers and grilles in length and width dimensions larger than our floor diffuser Models 531, 421, and 411. These products are limited in lengths to 14 inches and widths to 6 inches. Our linear series are not limited in length, but for constant foot traffic are limited to 8 inches wide. As the size of a floor product increases in both length and width, the strength must be there to meet the demands of foot traffic and code compliance. The 210 is the answer!

Model 210

Model 265


Another reason these are popular is because of our ability to build non-standard sizes of width and height. There are practical limitations of increasing size, however. Handling and shipping immediately come to mind. As strong as these products may be, one still needs to consider the end use. They are not meant to support fork trucks or grand piano legs, only humans walking over them. Another consideration is that if the International Mechanical Code is enforced, it requires floor registers to resist, without failure, a 200-pound concentrated load on a 2-inch diameter disc applied to the most critical area of the exposed face, usually the center. Although we do not punch mounting holes in the margin of these products, an installer may want to drill mounting holes for wall mounting in “high activity” areas where the products may be subject to damage—school hallways, gymnasiums, and social centers for example. In spaces where the installation is readily accessible and tampering with the damper may be an unintended result, consider using the Model 265 grille, then there is no damper that can be changed.


TT-13 March 2005 Fusible-link Dampers by Dave Fetters

Most of us understand what a fuse is,

at least as it relates to electricity—

a safety device that fails and

interrupts the circuit if the current

becomes too great. An old-style fuse

would melt an encapsulated wire or

metal strip due to heat build-up as

the current exceeded the fuse’s

rating. The fuse will no longer

conduct electricity after failing.

Today, however, most of us have

circuit breakers. We are going to

apply this concept of an old-style

fuse to a register damper.

One form of a fusible link is a set of

overlapping metal tabs with holes at

each end for attachment purposes

that will separate into two pieces at

a preset temperature. These over-

lapping tabs are held together with

precision solder that is temperature-

specific. A fusible-link damper is

the result of mounting a fusible link

to the damper of a register. The end

result is a register damper that is

fully operational as one would

expect, but has the added benefit of

closing if the temperature becomes

too hot.

Specifically, Hart & Cooley’s fusible

link is about an inch long with a

standard temperature rating of

165°F or an optional link with a

212°F rating. We use these on only

some of our steel multi-shutter

equipped registers like the 661 or

682. When the air temperature

passing over the link approaches the


rated temperature of the link, the

link will open (fail), allowing a

spring-loaded mechanism to slam

the damper shut and hold it shut.

The register is reusable by installing

a replacement link.

The links we use are Underwriters

Laboratories-listed components.

This means only the link has a UL

listing. Our use of one of these

fusible links on a register does not

transfer a listing of any kind to the

damper. These fusible-link registers

are not fire dampers and cannot

pass the UL requirements for listing.

They should never be substituted for

a listed fire damper.

The 661 and 682 in limited sizes

with metal handle are the only

fusible-link (FL) registers that we

offer.


TT-14 April 2005 Effective Area vs. Free Area by Dave Fetters

What are effective area and free area as they apply to grilles, registers and diffusers? What are the differences between these two areas and how are they used in our industry? Effective area, given the abbrevi-ation Ak (pronounced “A sub k”), is the area of the register, grille, or diffuser in square feet that is utilized by the air flowing through it. This is a calculated figure that can only be determined in our laboratory. It is used in the equation:

CFM = Face Velocity x Ak It is calculated by carefully measur-ing the Airflow Rate in Cubic Feet per Minute or CFM, and the Face Velocity in Feet per Minute or FPM. We then divide the Flow Rate by the

Face Velocity (Ft³/Min) divided by Ft/Min = Ft². The result is the effective area (Ak) in square feet. Notice that all the units match; that is, both sides of the equation use “feet” and “minutes.” You have seen this relationship before in TECH TALK TT-08, and you will be seeing it again in future discussions. The engineering data tables for all of our products are based on this relationship. In use, the actual CFM delivered by one of our products can be determined by measuring the average face velocity and multiply-ing it times the Ak for that size product found in our catalog Engineering Data. Free area is the sum of the areas of all the spaces between the bars or fins of a grille measured in square inches. It is sometimes called the


“see-through” area. If you were to measure the area inside the margin of a register face and then subtract out the area of all the bars, free area would result. Free area is different for each style of product. Rarely can a simple reduction in percentage of the listed size be applied to a grille to find its free area. There is no single formula that applies, either. Every product has a different set of input dimensions for calculating free area. When air flows through the bars or louvers of a product, it is com-pressed slightly between the bars, and there is some friction as the air makes contact with the bars as it flows past. This has the result of reducing the total area available for the air to pass through. Effective area is usually less than free area for the same product because of these reasons. If the engineering data of both supplies and returns use Ak, what is the need for free area? The answer is that some velometer manu-facturers ask the user to use free area multiplied by the measured instrument reading. (Hopefully, they ask that this area be converted to square feet.)

Some national codes, like the International Mechanical Code and the National Fuel Gas Code, also talk about the square inch “net free area” of grilles used to supply combustion air to gas-fired appliances in enclosed spaces. Again, free areas are commonly asked for and given in square inches, whereas Ak or effective area is always given in square feet. One can convert square feet to square inches by multiplying square feet by 144 (1 square foot = 144 square inches). The reverse is possible by dividing square inches by 144 to get square feet.


TT-15 May 2005 Sweating of T-Bar Ceiling Diffusers by Dave Fetters

Each year during the summer

season, we receive a number of calls

about moisture forming on the faces

of our T-bar diffusers or on adjacent

T-bars and dripping into the space

below. In the industry this is

commonly called “sweating.”

Moisture that drips into an occupied

space is annoying, and will

eventually cause rust to form on

steel diffuser faces and adjacent

T-bars. Sweating occurs more in

southern states that border the

coasts or in parts of the country that

experience high humidity levels as a

regular occurrence. Business

activities that rely on people coming

and going, like fast-food restaurants,

seem to be the most susceptible.

The doors are regularly opened,

allowing the hot, humid outside air

to sneak in. This begs for the air-

conditioning system to run longer

and colder, trying to maintain a

reasonable inside temperature.

Sweating occurs on diffusers when

warm, moist room air contacts the

cold diffuser face through aspiration

(drawn by suction) when the supply

air temperature is at or below the

dew point temperature. Dew point

is the temperature at which

condensation (moisture formation)

begins to take place. Most of us

have walked outdoors on a warm

and humid summer day carrying a

cold drink. It doesn’t take long

before the outside of the glass

becomes wet. Moisture is


condensing from the air onto the

colder surface of the glass. The

same thing is happening at the

ceiling diffuser.

Moisture can also form on the cold

back panel of a T-bar diffuser if the

temperature in the ceiling space is

hot and humid. This moisture often

runs down to the T-bar edges and

drips from there.

In an HVAC system, the occurrence

of sweating on a diffuser or T-bar is

the symptom of a system problem.

Removing a rusty, dripping diffuser

and replacing it with an aluminum

model will not make the problem go

away. The aluminum diffuser will

sweat; it just won’t rust. The

problem is that the supply air

temperature is lower than it should

be for the current conditions of

temperature and humidity. Banks

and similar public buildings are

other examples of spaces where

sweating occurs because of the high

volume of walk-in traffic and the

number of times the door opens,

letting in hot, humid outside air.

What can be done to minimize

sweating in an existing system?

One of the keys is to decrease ∆T –

the difference between room

temperature and the supply air

temperature. Doing this while still

meeting the load requirements

demands an increase in CFM. If the

air-conditioning unit is cycling,

switch to constant running. Look

for restricted return airflow because

of undersized returns or dirty filters.

Are the coils clean? If the unit is

shut down at night, consider

running at partial load to prevent

high humidity and room

temperatures at start-up. Is there

excess outside air mixing with the

return air?

We don’t claim to be experts in

system troubleshooting and problem

solving; therefore, we recommend

seeking guidance from a qualified

HVAC contractor to solve a sweating

problem. We address the issue

because the sweating manifests itself

first on our diffusers, giving a false

impression that the diffuser is at

fault.


TT-16 June 2005 Louver Performance and How to Size Them by Dave Fetters

Regular readers of this publication have seen the mathematical relationship:

CFM = Velocity x Area (Oh no, here he goes again!) This equation will always apply whenever we speak of moving an amount of air through one of our products. As before, the volume flow rate (cubic feet per minute or CFM) equals the velocity (feet per minute or FPM) times the area (square feet or FT²) of the product it is flowing through. Let’s apply this to the Hart & Cooley line of extruded aluminum stationary louvers. Customers generally have an idea of how much air (CFM) needs to be transferred through a louver and ask for assistance with sizing. “Sizing” a louver means to find a size that has

an area in square feet sufficient to pass the required quantity of air. Therefore, we need to solve the equation for area to determine the size. The equation above requires two out of three factors to be “known” to calculate a value for the third “unknown.” In order to find the correct “size,” the CFM and velocity must be known for us to determine the required area. When a customer wants to size a louver and only tells us the CFM, we have to ask “At what velocity?” Since velocity is related to pressure loss, we could arrive at a suitable velocity based on a planned pressure loss. (We will save this discussion for another issue of Tech Talk.) Hopefully you get the idea that somehow we have to determine a face velocity. The rest is easy.

CFM/Velocity = Area


Some recommended velocities for air intake, exhaust, or transfer are:

Exterior 500 – 700 FPM, up to 1,000 FPM if noise and water infiltration are not considerations

Interior 200 – 400 FPM for low pressure drop and low noise

Example: Size a 1½" thick louver

to exhaust 2,000 CFM from a mechanical room at 500 FPM.

Solution: 2,000 CFM 500FPM

So, from an area chart for a 1530 louver (1½ inch thick with a 30° blade angle), a 42 x 30 is the proper size that provides at least 4 FT². If noise is not a factor, maybe a 900 FPM velocity would work.

2,000 CFM 900 FPM For the same louver, a 30 x 24 is the correct size corresponding to this area.

Different louvers will have different areas for the same size because of differences in blade angle and depth of the blades. The area (in square feet) for the various louvers we offer, can be found in our Registers, grilles & diffusers product catalog and on our web site at:

www.hartandcooley.com

= 4 FT²

= 2.22 FT²


TT-17 August 2005 T-Bar Diffusers with Molded Fiberglass Back Panels by Dave Fetters

Quite a few of the Hart & Cooley lay-in T-bar diffusers and return grilles use a molded fiberglass back panel or plenum. The molded fiberglass backs have some significant features.

Bonded foil vapor barrier

Prescored for different collar sizes

UL 181 Erosion and Impact tested

Meets ASTM E84 for 25/50 code compliance

4-inch deep cavity

“R” values of 4.2 and 6

Approved for the city of Los Angeles

Labeled with code information

Fiberglass back panels allow for the use of various collar styles like spin-in, tab-in, or our own 5400 Series Collar Ring (6-inch through 18-inch diameters). The use of the 5400 collar allows for the installa-tion of our 3800, T19, or RD round dampers, either at the time of installation or later.

Fiberglass Back Panel NOTE: Attachment of molded

fiberglass back and 5400 collar requires 5400PP (push pins).


The 5400 collar was originally designed for, and is still used on, our metal-backed T-bar products like the HVS/FPD and others. As such, it

comes with four small plastic push pins that snap into

the prepunched holes in the metal plenum. If one chooses to use the 5400 collar with the fiberglass back panel, a different but similar mounting system is employed.

Cut the four small plastic push pins off of the 5400 collar plate.

Cut a hole in the fiberglass back panel to match the collar size.

Lay the 5400 collar on the back panel.

Punch holes in the back panel with a screwdriver or awl using the plate holes as a template.

Push the 5400PP push pins up through the back panel holes from the inside and through the holes in the plate.

The large head on the black plastic push pins (5400PP part number 014525) should be snug against the fiberglass back on the inside, and the “Christmas tree” legs should grip the holes in the collar plate tightly.

This collar attachment system works for the following products.

5400PPPush Pin

659TI 96AFBTI

PFTI RE5TI

REN4 RENPS

RENP

5400 Collar


TT-18 September 2005 Repainting Grilles, Registers and Diffusers by Dave Fetters Since we are often asked how to repaint our registers, the answer sounded like a good Tech Talk subject! Every part, whether it is made from steel, aluminum, or plastic, whether painted or anodized, can be repainted. A common starting point for any product is to ensure a clean surface. Paint will not stick to a dusty or greasy surface. Just wipe off a dusty surface with a clean, dry cloth. If grease or a similar contaminate is present, clean with a mild dish detergent or diluted alcohol to cut the grease, then dry thoroughly. DO NOT use aggressive chemical cleaners like lacquer thinner, MEK (methyl ethyl ketone), acetone, nail polish remover, PVC cleaner, bleach and the like, because they will eat into the existing paint or, on plastic, attack the surface.

Lightly rubbing the hard, glossy finish of our product with fine steel wool or a Scotch-Brite® pad allows the new paint to adhere better. Priming is not required. A couple of light color coats are preferred over one heavy coat. Spraying will provide better coverage than brushing. Lacquer, latex, and urethane-, acrylic- or PVC-based paints all work, even on the REZZIN™ products. Krylon® Fusion and H2O™ work well. If spray lacquer will be used, be sure to shake the can well; otherwise, the thinners and paint in the can may not mix, and the result could damage the surface to be painted.


TT-19 October 2005 Alternate Sizing of the 821/831/92/HV Series Registers by Dave Fetters We publish a significant amount of performance data for the series of products listed above. We also duplicate the data for the sizes shown in the tables for four different deflections, since the blades in the register face are individually adjustable. The sizes listed in the tables cover a range of popular rectangular products, but by no means the full extent of the sizes we can build. In addition, we do not show data for square sizes or for those with a width less than the height. For instance, the extruded aluminum HD series can be built in any 2-inch dimension from 4 x 4 to 48 x 48—more than 500 combina-tions! Obviously, we cannot publish performance data for all these sizes. How can you determine perform-ance for a size not listed (without calling us, of course)?

The last page of the Engineering Data at the back of our Registers, grilles & diffusers catalog shows an “Alternate Sizing Graph” for these products. This graph provides a method of using “equal areas” to find a listed size that has the same approximate performance as the desired size that is not listed. Testing indicates that by varying the dimensions of a grille while main-taining the same area, there is little effect on the airflow. The relation-ship of the width to the height of a grille is called the aspect ratio. A 16 x 12, which is not shown in our data, is approximately equivalent to a 24 x 8 in performance, which is shown even though the aspect ratio has changed. We have just determined the performance of our desired size by looking at a listed size with equivalent performance.


When performing these compari-sons, remember to stay with the same blade deflection represented by our designations A, C, E, or G. These deflections are described at the very back of our catalog near the alternate sizing graph. The same alternate sizing can be accomplished by using a calculator through trial and error. The numbers don’t always come out perfectly. For example, let’s say we are locked into a retrofit size register of 14 inches wide by 22 inches high, and we want to find out how it will perform at various face velocities.

14 x 22 = 308 square inches We now need to divide 308 by various widths appearing in our performance data to find a depth that is close to a size that is listed. I started by dividing 308 by 20 and got 15.4, which doesn’t match anything. I tried 24, 30, and 36 as well and found that at 30 inches wide, I got 10.26 inches high. It’s not a perfect match, but it is close enough to the 30 x 10 listed in our tables, which gives us a reasonably accurate series of performance numbers based on changing face velocity. This same analysis cannot be applied with any degree of accuracy for other face designs like adjustable curved-blade registers or stamped louver supplies and returns. There are other tricks to generate perform-ance data that use a method called

extrapolation, using data from listed sizes to project what the perform-ance will be for unlisted sizes. I’ll save this topic for later so that I don’t overwhelm you all at once.

Blade Deflection

©2005 Hart & Cooley, Inc. All rights reserved (continued on reverse side)

TT-20 November 2005 Grille, Register and Diffuser Substitution by Dave Fetters

For whatever reason, you may not be able to find the exact model of Hart & Cooley grille, register, or diffuser product you had hoped to. Given the fact that you may not have the option to change the size of the desired model to get by, what options do you have to substitute another model for the one you wanted? Since Hart & Cooley has the broadest product offering in the industry, chances are very good that a suitable substitution can be found. Allow me to offer some suggestions for substitutions without concern for the obvious variable of cost. This discussion should help broaden your product knowledge about the use of alternates. Materials, construction, designs, and features may change, but the end effect of adequate (or enhanced) performance will still be achievable. Floor: An alternate for our popular 421 steel floor diffuser could be a 411, 531, or a Linear in an ascending order of capability. The steel 411 is more robust than the 421 and could be used in high traffic areas. A 531 is constructed of extruded aluminum for a premium look, has high strength, and offers a unique way to both heat and cool from the same

location using dual multi-shutter dampers to change the air pattern as necessary. Linears offer the greatest available range of lengths (almost unlimited) and widths, are made of extruded aluminum, can be used as a supply or return, and can be used in the floor, on the wall, or in the ceiling. The Linear series has a large matrix of possible sizes, when you consider that widths are available in half-inch increments from 1½ to 12 inches (for floor applications) and up to 24 inches for wall or ceiling use combined with infinite lengths. The 210 supply registers and 265 return grilles could be used as substitutes for sizes of floor registers that are not available in the 421, 411 or 531 styles. Baseboard: Baseboard diffusers do not have the luxury of a wide range of common sizes. However, the 654, 655, and 664 are interchangeable, for the most part. We offer 406, 462, and 464 base-board diffusers, as well, in longer lengths and various materials and finishes. Sidewall/Ceiling: Alternates for our louvered sidewall/ceiling registers, like the 661 ⅓-inch and 682 ½-inch fin-spaced designs, would be one for the other if you


were not concerned with blade spacing. An option for these steel registers is the plastic RZ680 series that has the advantages of molded-in color and rust resistance, but the size offering is limited. The ultimate in sidewall/ceiling products are the 92 series in steel and the HV series in extruded aluminum. These products offer the widest range of sizes and options, including stronger construc-tion, multiple damper choices, single or double deflection, adjustable blades, and matching returns and filter grilles. Curved-blade registers start with the 300/A300 series, progress to the A611-A614MS/OB adjustable curved-blade registers, and finally extend to the C series extruded aluminum registers. The 300/A300 series of stamped, fixed-blade registers have a multi-shutter damper. The assembled A600 series adjustable blade registers offer a choice of multi-shutter and opposed-blade dampers. Faces and blades are made of aluminum with painted galvanized steel dampers. The C series of adjustable curved-blade registers also have a choice of multi-shutter and opposed-blade dampers, as well as a comprehensive size matrix in 2-inch increments. White and satin anodized aluminum finishes are available. These are assembled using premium aluminum extrusions. Return Grilles: The 650 and 672 stamped-face, louvered return grilles could be substituted for one another (as before, there is a difference in blade spacing) before moving to the 94, 94A, RCB, RE5, RH90, or RH45 return grilles. The latter group is usually considered “commercial” because these are assembled rather than stamped. They have stronger construction and offer more features, especially size options. Filter Grilles: We start with the “residential” type 659 and 673 with stamped louvered faces that are inter-changeable as far as performance, even with the difference in blade spacing. There is a large number of sizes offered. The commercial filter grilles—96AFB,

RHF45, REF5, and RCBF—are more robust, being assembled of steel or extruded aluminum, and offer many more sizes. Ceiling Diffusers: Round ceiling diffusers are limited to our 16, RZ16, or 20 diffusers. A square diffuser could be substituted for a round diffuser with little change in performance. The 16 is a non-adjustable, steel, step-down diffuser. The RZ16 is a plastic flush diffuser with a 12-inch face, but it has built-in 6-, 7-, and 8-inch collars. These come with a cam-lock installation method, removable core, and built-in damper. The 20 diffuser is a heavy duty, adjustable core diffuser for commercial and industrial applications. Square diffusers include the 24, RZ500, SD, the A500 directional series, the MCD modular core diffuser, and the SR/AR series, again in ascending order of features and size offerings. The 24 is a steel, step-down diffuser with butterfly and opposed-blade damper options. The RZ500 is the square equivalent of the RZ16 described above. The SD step-down is an all-aluminum diffuser that can be used in high humidity applications. An MCD modular core diffuser is made from extruded aluminum and allows for 1-, 2-, 3-, 4-, and 2-way corner airflow patterns. It is offered in two margin styles, nine sizes, plus an available T-bar mounting, with or without damper. The SR/AR series has the greatest number of options of sizes and face styles in both steel and aluminum for any ceiling diffuser in our lineup of products. Not all of these are suited for residential applications, however. A substitution may not always be avail-able or welcome, but if the opportunity occurs, the preceding should be helpful.


TT-21 December 2005 Working with Standards, Codes, and Inspectors by Dave Fetters

The products we develop, sell, and

use in our HVAC industry are

subject to testing to Standards,

installing to Codes, and inspection

for approval by Inspectors. As an

example, our Type B gas vent is

Underwriters Laboratories-listed to

their Standard 441; it must be

installed according to our

instructions as required by The

National Fuel Gas Code and must be

inspected for compliance before

being approved for use.

A Standard is a widely accepted

consensus document, developed

over time by those knowledgeable in

the industry, and is used as a basis

for measuring, evaluating, or judging

the quality and performance of

products. Usually, products listed

by a recognized agency and tested to

an industry-accepted standard have

met a certain minimum level of

performance, allowing everyone to

feel secure in the knowledge that, if

installed properly, the product is

safe for its intended use. Listed

products require a label attesting to

its approval.

A Code is a systematic document of

rules given statutory force by an

adopting governmental agency.

Codes are written to safeguard life,

health, property, and public welfare.

They provide a foundation from

which consistent understanding and

enforcement can take place. Codes

will require appropriate products to

be listed and installed according to

the manufacturers’ installation


instructions. Codes usually do not

prevent the use of materials,

methods, or procedures not

specifically prescribed by it, but

they may require evidence to

substantiate claims of equivalent

performance or safety of

alternatives.

The Inspector is the authority

having jurisdiction designated by the

governmental agency. The inspector

administers and enforces codes by

inspecting installations during

construction, or at least before use

or occupancy.

Installers and inspectors, working

together, will minimize conflicts.

Misunderstandings will occur and

disputes will arise, but letting the

issue become confrontational is

inadvisable. Usually, it becomes a

matter of discussing the issues for

resolution. Contractors/installers

should know the product, the

installation instructions, and which

codes apply.

Hart & Cooley is able to help with

questions about codes and standards

as they apply to the products we

sell. We have people on staff who

have been members of codes and

standards writing bodies for many

years. We conduct training to

installers and to inspectors on

portions of codes that apply to our

products.

Whenever someone calls for help,

we need to deal with clear and

concise facts. Be prepared to

provide comprehensive and detailed

information with documentation if

necessary. We can only deal with

the information provided to us. If

the information is inaccurate or

incomplete, it could affect the

outcome of the disagreement.

Call us, fax us, or contact us by

e-mail through our web site at

www.hartandcooley.com.


TT-22 January 2006 Dimensions of a Grille, Register or Diffuser by Dave Fetters

Sometimes, those of us in the HVAC industry assume our customers understand the everyday lingo we use in helping describe our products. Have you ever stopped to realize what the “size” of a register means or where one measures the size? Usually a size is given in inches and it refers to the two dimensions of a square or rectangular register. The size can also be a single dimension that refers to the diameter of a round diffuser or the “square” of diffusers that are only offered in square as opposed to rectangular sizes.

Let’s look at the simple example of a 12 x 6 sidewall supply register. The model doesn’t matter. The dimensions 12 and 6 are inches. By convention in the industry, the first dimension is the width of the register. So looking at the register, the 12-inch dimension is the left-to-

right (horizontal) measurement. That leaves the 6-inch dimension as the height or up-and-down (vertical) dimension. To refer to this product as a

6 x 12 would imply that the 6-inch dimension is the width, because it is the first dimension given, and the height 12 inches. This would not look right on a wall nor would the fins be oriented in the proper direction for its intended use.

width (horizontal)

height (vertical)


Big deal, you say? Have you ever tried to find the 12- and 6-inch dimensions on a register? They aren’t there! The dimensions are called nominal, meaning “in name only.” The nominal dimensions or “listed size” of a register refer to the hole, boot, stack head, or duct opening. The industry builds the damper on the back of a register undersized with reference to the nominal dimensions so that the damper will fit into the opening. A submittal drawing of the part may show the damper dimensions as “listed size minus 3/8” which means that for our example, the damper dimension would be 115/8 by 55/8 inches.

The margin or outside face dimensions are oversized compared to nominal. They may be “listed size plus 1¾” inches so that the face will easily overlap the 12 x 6 mounting hole. Our example register would have face dimensions of 13¾ by 7¾ inches.


TT-23 February 2006 Sidewall Vent Terminations by Dave Fetters

We are often asked if our models RHW and RM gas vent caps are suitable for use on a sidewall vented appliance. Background: Many unit heaters allow sidewall venting as an option to a vertical vent. With vertical venting, the hot flue gases rise in the vent creating a negative pressure in the vent. The vent joints are not required to be leak-proof or sealed, since the atmospheric (positive) pressure outside the vent is higher than the negative pressure inside the vent during firing. Leakage, should it occur, would be from the outside of the vent to the inside—from the area of higher pressure to an area of lower pressure.

When unit heaters or other appliances are vented horizontally, the performance characteristics of the vent change. Flue gases do not naturally flow horizontally. The small combustion air blower in the appliance now pressurizes the flue gases slightly. This pressure in the horizontal vent is slightly positive

(higher than) atmospheric pressure. Leakage of flue gases could now possibly occur into the occupied space. Therefore, the single-wall vent joints must be sealed.

Cap performance: Our RHW and RM caps are tested to Underwriters Laboratories standards requirements that must be met when installed in their natural position on top of a vertical vent.

RHW Cap RM Cap


These tests are oriented toward a vent system operating with a negative pressure. These UL standards do not address performance of these same caps for a horizontal, positive pressure vent. Horizontal vent performance requirements for the gas-fired appliance certification process are part of the ANSI Z21 series of standards. When an appliance is tested with a horizontal vent system, the appliance manufacturer must specify which cap(s) should be used with their appliance, based on these test results. In other words, for the Hart & Cooley caps to be used for sidewall vented appliances, they must have been tested and approved for use with that appliance. To date, our RHW and RM caps have not been tested with any appliance, that we know of, and should not be used for sidewall vent terminations without the approval of the appliance manufacturer. What difference does this make? Sidewall terminations must have Fuel Gas Code-specified distances from adjacent public walkways, buildings, operable windows, and other building openings for obvious reasons. More importantly for proper performance of the appliance, the ignition, firing, running, and shut-down sequences must perform in a nominal fashion without undue delays or interruptions with a 40-mph wind blowing on the vent termination. The amount of carbon monoxide developed during testing must not exceed .04%.

The amount of static pressure that builds up around a horizontal vent cap depends on wind speed, wind direction, and how close the cap is mounted to the sidewall. Both increasing wind speed and shorter cap distances to the wall will increase static pressure to a point where the furnace may not vent properly. Clearly, the appliance manufacturer does not want a vent termination to extend out from a building wall 4 feet just to overcome the cap’s poor performance in the wind test. Six to 12 inches is usually an acceptable distance that will work with a proper cap tested with the appliance. Again, our caps have not been tested for use as horizontal terminations.


TT-24 March 2006 What are the Considerations in Sizing a Return? by Dave Fetters

In a previous Tech Talk, we discussed return grille locations (TT-09). This time we will look at sizing return grilles. As we have stated before, return air volume to the air handler (fan) must equal what is supplied from the air handler, otherwise system perform-ance will suffer. Not all the air that is returned may be from the occupied spaces. Some make-up air may be brought in from the outside. No matter the mix of indoor to outdoor return air, the fan needs to see the same volume coming in as it sends out. If the system requires 80% of the supply air volume to be returned through grilles, the amount of airflow through each depends on the number of each. A 2000 CFM system returning 80% will require a single filter grille to handle 1600 CFM, four return grilles to handle 400 CFM each, or some other combination.

The return air grilles or return air filter grilles should be unobtrusive during fan operation. This means paying attention to the face velocity when sizing these grilles so that humming or whistling noises do not occur. These noises are symptoms of face velocities that are too high. In filter grilles, this may also indicate that the velocity is higher than the rating of the filters. General recommendations for resi-dential return grille maximum face velocities are about 600 Feet-per-Minute (FPM) for grilles and 400 FPM for filter grilles. These products usually have stamped louver faces (Model 650).

650 Return Air Grille


Special consideration must be given to master bedroom suites and home theater rooms where lower velocities may have to be considered to guarantee no noise. Assembled grilles using heavier steel or extruded aluminum will not share the humming noise with their stamped-face cousins, but can make

airflow noises if the velocity creeps up (Model RH45). The room activity and background noise level will help dictate how high the face velocity may

extend. A noisy cafeteria or busy lobby can afford higher velocities than executive offices or libraries. Once a reasonable face velocity is determined for the type of grille being considered, use the perform-ance data in the back of our catalog or from our web site to size the grille. Under “Face Velocity” for the style grille being considered, go down that column until the CFM figure equals or slightly exceeds the volume flow rate necessary. Without benefit of the catalog, a rule of thumb is to plan for 2 CFM for each square inch of gross grille area. This rule will keep you within a safe face velocity.

A 20x20 grille has 400 square inches of gross area. If the “2 CFM/square inch” rule is used, 800 CFM is what the grille will handle with a low enough face velocity to avoid noise. For our 650 grille, using this method results in a face velocity of about 430 FPM. This rule is a little conservative for grilles, but much closer for filter grille performance.

RH45 Grille


TT-25 April 2006 Sizing of Flexible Duct by Dave Fetters

Flexible duct has many advantages in the HVAC environment. Its ease of use and timesaving (money) speed of installation compared to hard duct is inviting. But using it as a direct size replacement for smooth, galvanized duct is not one of its advantages due to a difference in performance. Because of flex duct’s unique corrugated construction and flexibility, there is a higher airflow friction loss compared to the same size smooth-walled galvanized duct. Performance equivalent to hard duct requires a larger diameter flex duct.

Friction loss in straight duct is dependent on the relationships of duct diameter, air velocity in the duct, and duct roughness as major components, and to a much lesser degree on air density. As one can

imagine, flex duct with its helical corrugations is going to be much “rougher” or less smooth than galvanized duct. This is especially true if it is not stretched out to the extent possible during installation. Slack duct allows

the coils of reinforcing wire to relax, which bunches up the polyester and pushes it into the interior of the core, adding more resistance to airflow.


Sizing charts and calculators for duct sizing are available from many sources. Hart & Cooley has a Sheet Metal Duct Friction Loss Calculator on one side of a slide chart with a Flexible Duct Friction Loss Calculator on the other side that we make available. We also have an interactive flex duct calculator on our web site. Spending a few minutes with these aids can quickly demonstrate the differences between the friction losses for galvanized verses flexible duct. It is worth noting that for a fixed duct diameter, as the velocity in the duct increases, the friction loss increases twice as fast. So if the velocity were to double, the friction loss would be four times greater! A handy rule that is very effective and reliable is to increase the size of flex duct one diameter to neutralize the added friction loss compared to that of galvanized duct for the same CFM. A further penalty in performance will occur if flexible duct is compressed from its round shape to an oval shape, say by squeezing it into a joist space. Just because it can doesn’t mean it should. We do allow for up to approximately a 20% reduction in diameter only if it occurs in one spot, but not over any distance or repeatedly. The friction loss for flex squeezed into an elliptical shape over any distance is severe, and the loss of airflow will be significant.

Cubic feet per minute airflow rate still equals the air velocity times the area of the duct in which the air is flowing. Increasing the area of the duct will slow the velocity of the air and reduce pressure loss. Keep in mind that the long-term system performance will be affected by the up-front, one-time cost of the flex duct. Increasing flex duct one size to offset its higher pressure loss compared to smooth duct is prudent.


TT-26 May 2006 Cleaning Chimneys by Dave Fetters

It probably strikes you that this is an odd time of the year to be hearing about cleaning chimneys. Yet, cleaning a chimney in the spring, at the end of the heating season, is one of the most important elements of properly maintaining a chimney system. We want folks who have installed our chimney to enjoy the value of their investment by having the satisfaction that, with proper care, the chimney will have a long, safe life. All fuels have some contaminants in them. Some, like coal, contain more than others. Burning trash, workshop scraps, and other burnable matter that cannot be

classified as purely a “fuel” can contain very harmful chemicals. These chemicals may end up on the chimney walls as part of the creosote, soot, ash or debris that

builds up over time when burning any fuel. Most people realize that creosote buildup in a chimney needs to be addressed on a regular basis. But, as one’s train of

thought frequently goes: “There isn’t enough junk on my chimney wall to be dangerous, so I’ll clean it later.” Just because the condensed material on a chimney flue may not be creosote, which can build up thick enough to start choking off the flow of gases, doesn’t mean it isn’t harmful, if not dangerous. Creosote can be highly flammable and, if

Creosote can be highly flammable and, if

ignited, can create a severe chimney fire—

that’s dangerous!


ignited, can create a severe chimney fire—that’s dangerous! Soot, on the other hand, is not normally thought of as “dangerous,” nor does it build up layers thick enough to affect the draft. It’s only thought of as annoying, if it is thought about at all. But left alone, soot containing harmful acidic compounds can harm the chimney. Oil and coal fuels contain sulfur. When burned, the sulfur becomes sulfites and sulfates that end up being carried out in the flue gases. If these compounds trapped in the soot are allowed to sit in the chimney for long periods of time, say all summer, the moisture in the air will combine with the sulfur compounds to form acids. These acids then begin to eat away at the stainless steel. We ask that chimneys be cleaned at the end of the heating season to minimize the possibility of harmful residue remaining on the chimney wall during the off season. The sooner the chimney is cleaned after the last use of the appliance the better.

Thoroughly brushing the chimney is usually adequate to mechanically remove any buildup of soot or creosote from the interior of the

chimney for intermittent cleaning during the heating season. We recommend a final pass down the chimney be made with the brush wrapped in a rag. At the end of the season, spray the rag-wrapped brush with WD-40 for the very last pass down and back

up the chimney. This will help remove all residual soot from the surface and leave a protective film on the interior throughout the summer.


TT-27 June 2006 Flexible Duct Tape and Non-metallic Clamps by Dave Fetters

Tape As an added service to our flexible duct and connector customers, Hart & Cooley sells an Underwriters Laboratories-listed tape specifically for use with flexible duct as required by national standards. This tape is labeled “UL 181B-FX” both on the package and on the tape. We offer rolls in both black and silver to match the color of our flexible duct jackets. Tape is used for both sealing the duct to collars, as our instruc-tions state, and to seal rips and tears in the jacket should they occur.

Generic “Duct Tape” is sold and used for many applications other

than for sealing ducts. There are different grades and levels of performance, but, unless it is UL-listed 181B, it is not approved for flexible duct applications. There is a UL 181A tape specific for duct board, and neither should be substituted for the other. Generic tape is mostly cloth-backed with a water soluble, rubber-based adhesive that is sold in 60-yard rolls. Hart & Cooley’s duct

tape is a polypropylene film with a


solvent-based adhesive that is sold in a 120-yard roll. It also has higher tack and adhesion, a longer shelf life, and a flame and smoke rating of 25/50—suitable for commercial applications. It is a tough material, yet can be torn by hand. The

functional temperature range is -35° to +260°F—better than cloth tapes. Non-metallic clamps Non-metallic air ducts and connectors are required by industry installation instructions to clamp the core to the collar. This can be accomplished with either metallic hose clamps or with listed non-metallic clamps labeled in accordance with UL standard 181B and marked “181B-C.” This UL standard is a relatively recent development for these non-metallic clamps. Prior to this portion of the standard, each flexible duct manufacturer would have to test at significant expense each non-metallic clamp to be specified. We now have a list of 9 different manufacturers that have multiple models listed with UL.

Ducts must be reasonably airtight to prevent leakage and noise for reasons of energy efficiency, humidity control, cost, temperature control, reduced maintenance and general acceptability. Since most systems are not pressure-tested before being approved, the codes insist on the use of UL-listed materials and prescriptive methods of attachment and sealing that, if followed, will ensure consistently tight joints.


TT-28 July 2006 Using a Digital Airflow Meter by Dave Fetters

There are at least a dozen airflow meters (also called anemometers or velometers) that are now on the market and relatively affordable to an installer or service technician. These are generally small, hand-held, propeller-type digital meters that read air velocity in feet per minute (FPM). Many are capable of measuring temperature and, by entering the area of a register in square feet, calculating cubic feet per minute (CFM). Accuracy is advertised at ± 3% within an airflow range of about 150 – 5000 FPM. Most have large digital

LCD readouts, read in US or metric, and have averaging as well as

min/max capabilities. For most residential and commercial work, these meters will measure airflow at the face of grilles, registers, and diffusers to aid in balancing and diagnostics. They can also be used to measure air velocity anywhere in a room to study

airflows, look for drafts, and determine

throws by looking for the terminal velocity of a supply register.

Illustration from Universal Enterprises, Inc.

www.ueitest.com


We were curious about these instruments, so we tried a few over the years in our laboratory and compared them to our expensive, calibrated, hot-wire anemometers. In a word, they perform well enough for one to get a good idea of the air velocity. Some are more accurate than others, with accuracy declining toward the low velocity readings. A little experience is helpful in the use of these devices, but does not significantly improve the outcome. More important to proper use is to understand a little about airflow and the expected result, at least within the ballpark! The single biggest shortcoming that we saw on a consistent basis was in the lack of clarity of instruction manuals. Reading face velocity with these instruments is straightforward. One of the keys to obtaining a good face velocity is by averaging many readings covering the entire face. However, when the instructions say how to obtain CFM, some make a glaring error by asking the operator to enter the free area. Not only that, but the instructions may not clearly state whether this area should be in square inches or square feet.

Anyone following Hart & Cooley’s Tech Talk newsletters should know by now the CFM = Velocity x Area relationship that I’ve mentioned in previous issues—Numbers 8, 14 and 16. The units of the quantities on both sides of the equal sign must be the same. Cubic feet per minute appear on the left of the equal sign. Velocity on the right side is in feet per minute. Therefore, the area must also be in square feet—effective area in square feet to be accurate. We provide the effective area (Ak) in square feet in the performance data for all our products. This is what should be entered into these meters, NOT the free area typically given in square inches (if one can find it at all). We did not find any meter that would accept free area in square inches and convert it internally to the square feet that is required. Beyond the above, which remains very important for good results, we found the meters to be adequate for the job and certainly better than nothing.


TT-29 August 2006 Dirt Stains on Diffusers and Adjacent Ceiling Surfaces by Dave Fetters

We’ve all seen them – ceiling diffusers that are dirt-stained, and the dirt stains usually extend to the surrounding ceiling surface. It is unsightly, especially if one is waiting for a meal in a restaurant. A first reaction from those outside our industry is “Wow, the filters need to be changed.” Hopefully, those of us involved in HVAC businesses know that dirty or poorly functioning filters are not the sole or most common cause. Investigations have shown that “smudging,” as we call the deposition of dirt particles on the air outlet and surrounding surfaces, is more likely to be generated from room activity that releases dirt into the room air rather than from dirty

supply air. This dirt suspended in room air, called an “atmospheric aerosol,” can then be entrained (drawn) into the discharge of the diffuser. Additionally, diffusers with tumbling air patterns that contact

the ceiling, such as the RENPS, are more likely to generate smudging on the ceiling. This is in contrast to a register that blows air angled away from the mounting surface, such as the 682, although dirt may still stain the diffuser.

Dirt particles can be composed of both natural and man-made materials that are generally common in the immediate area. The amount varies with the geography, season, weather, room furnishings, room construction, and activity. Dust, carpet fibers, tobacco smoke, greasy

…dirty or poorly functioning filters are not the sole or

most common cause.


fumes, lint, and pollen are some of the particles deposited. The smallest particle sizes are the worst offenders. Heavy foot traffic through a room will stir up these fine particles and keep them in suspension. Cooking, printing, paper dust, and smoking are some other contributing activities to smudging. One interesting example occurred in a new local food store near our offices. Dust from the coffee grinder produced an obvious brown blossom on the ceiling around the diffuser that was located above the grinder with nothing appearing on the more remote outlets, even though they were on the same air system. How can we control (notice I didn’t say “eliminate”) smudging in susceptible areas? A combination of keeping the air filters clean, frequent mopping and vacuuming of floors, and room air cleaners can all help, but may not be practical in many areas. A careful selection and mounting of air diffusers will minimize dirt smudging, but recognize that we are addressing the symptoms, not the problem. A diffuser with a beveled or step-down margin like our SRS/ARS will help deflect the air in a slightly downward angle, keeping the air from contact with the ceiling and, hopefully, lessen dirt staining on that surface.

Another potential solution is to use our Surfaire® or REN4 diffusers that generate a very thin air stream tight to the ceiling that prevents dirt-laden room air from entering the minimal space between the supply stream and the ceiling. Some dirt will still deposit on the aluminum face at the edges of the air pattern and in the center where there is little airflow. These stains on an aluminum diffuser are easy to wipe off compared to ceiling materials.

What we are trying to do is prevent the entrained room air that suspends the dirt particles from reaching the ceiling surface where the forces of electrostatics, vapor pressure, direct impingement, and temperature difference cause the dirt to stick. The (relatively) high velocity of the supply air stream creates a localized lower pressure that the room air-suspended dirt will want to flow toward. As my wife likes to say, “Nature abhors a vacuum” (which she learned from me). That’s another way of stating that air will flow from a region of high pressure to one at a lower pressure. Keeping this supply jet off the ceiling surface can help reduce staining.

SRS/ARS

Surfaire®/REN4


TT-30 September 2006 Finding Performance Data for Unlisted Size Registers by Using Listed Sizes (Interpolation or Extrapolation) by Dave Fetters

I know what you are thinking: “Oh no, here comes another math lesson. I don’t even know what those big words mean!” Well, you’re right. This is going to involve math to some degree, but only simple addition and multiplication. It’s more about teaching you the concept of sizing a register or grille for a size not shown in our performance data tables, based on data for a size that is shown (to interpolate or extrapolate). Interpolate means working within the maximum and minimum table entries to find data for a size that falls between two listed sizes. Extrapolate means to project known data from a listed size for a size that falls beyond the largest size listed. Previously in Tech Talk TT-19, I mentioned the alternate sizing graph in the back of our catalog as one means of finding performance data for the 821/92/HV series products for

sizes that are not listed based on sizes that are. I also mentioned using a calculator to find a listed size register that has similar gross square inches as the unlisted size. By using the data for the register that is close in equivalent area, you will have a good idea of its performance. This is sometimes called “the equal area method.” This is an iterative process in that it requires a “trial-and-error” approach until a solution is found. We will again use the 821/92/HV series products as examples, although this same discussion can be applied to many other products as well. These products lend themselves to the discussion because of the numerous sizes that are listed, with which I will demonstrate both interpolation and extrapolation. Let me begin by saying that any alternate sizing must remain not only within the same deflection (A, C, E, or


G) table, but also under the same column of face velocity. My examples will all be from the Deflection A performance data and in the 400 Feet-per-Minute face velocity column for simplicity. The principles apply to any deflection and face velocity, however. A 24 x 12 register will be twice as large as a 24 x 6 register. A 24 x 24 is two times larger than a 24 x 12 and four times larger than the 24 x 6. But a 12 x 6 is ¼ the size of a 24 x 12. See the representation below.

24

12 x 6 12 x 6

12 x 6 12 x 6 12

If a register is twice as large, it will allow twice as much air to pass through at the same face velocity. I use these sizes since one can look them up in our catalog to follow along. Going from 24 x 6 to 24 x 12 will demonstrate a doubling of both the size and the CFM (310 to 635). Likewise, doubling a 10 x 6 to a 20 x 6 will double the CFM from 125 to 255 (with rounding). This is interpolation within the table entries. If we wanted to extrapolate from the 20 x 6 to a 40 x 6, the CFM would double again from what it is for the 20 x 6 (255) to about 510 CFM for the 40 x 6. You can check this by using the alternate sizing chart in the back of our catalog to discover that a 40 x 6 has equivalent performance (and area) as a 24 x 10 or 30 x 8, both of which are listed in the table. The 40 x 6 has 240 square inches of gross area and shares this number with both the 24 x 10 and 30 x 8 (equal area method).

Examples: An 18 x 12 is not a size that is listed, but a 36 x 12 is. If we take half the CFM of a 36 x 12, it will represent the CFM for the 18 x 12 at the same face velocity. CFM for an unlisted 36 x 24 will be twice that of the listed 36 x 12 and for an unlisted 36 x 36, three times that of the 36 x 12. Be sure to keep in mind what constitutes twice the size as opposed to four times the size of a register. Doubling one dimension only will double the size while doubling both dimensions will quadruple (4x) the size. One last comment: To determine a rough throw result, use the multiplication factors below. If you:

Double the size and CFM, multiply the throw by 1.5

Quadruple the size and CFM, multiply the throw by 2

Half the size and CFM, multiply the throw by .67

One quarter the size and CFM, multiply the throw by .5

By now, most of you are probably thinking, “I’ll never remember how to do this. It’s a lot easier to just call Hart & Cooley and ask for help.” We remain here to do just that, but file this Tech Talk for reference.


TT-31 October 2006 Curved-Blade Register Discussion by Dave Fetters

Hart & Cooley’s product offering includes both fixed and adjustable curved-blade registers used for high sidewall and ceiling applications. The fixed curved-blade series is the (A)300 one-piece, stamped-face register in one-, two-, three-, and four-way deflections with either steel or aluminum faces. Adjustable curved-blade registers come in two different series—the residential A600 series made with a stamped aluminum face and roll-formed aluminum blades and the commercial C series made entirely with extruded aluminum.

The reference to residential or commercial is mostly in name only. We see either product used in either application. Commercial product is usually distinguished by more options and a much larger size offering. All three series offer all four deflections. The C series, made from extruded aluminum, is the premium product because of its considerable strength advantage over the roll-formed product. In addition, the C series is offered as a grille (no damper) and as a register with either a multi-shutter or

(A)301 fixed (A)302 fixed

(A)303 fixed (A)304 fixed

A611 adjustable A612 adjustable

A613 adjustable A614 adjustable


opposed-blade damper in 2-inch increments from 6 x 6 to 36 x 36—a much larger matrix of sizes and options than the A600 series. These are some of the reasons why the C series costs more than the A600 series—added features. The performance data of the A600 and C series product lines are very similar, providing that the blades are set to the same opening dimension. The 300 series is not included in this discussion since the blades are fixed. A significant advantage of adjustable curved-blade registers is the ability to open or close the blades to suit the room comfort requirements. Consequently, performance depends on how far the blades are open with respect to how much air is available at the face. With this in mind, consider a narrow blade opening for a ceiling-mounted register. A small gap between blades constricts the airflow, which usually increases the velocity and resistance (for a set CFM, reducing the area increases the velocity if the fan can work against the added resistance). The result is an air pattern that is tight to the ceiling surface at a somewhat increased velocity that will maximize the throw. This is a great cooling pattern. At the extreme opposite blade setting with all the blades open to the maximum, the air is no longer deflected into discreet directions along the ceiling, but allowed to blow straight downward or outward. This is the best way to introduce warm air from the ceiling into the occupied space with this type product. Since conditioned air above ambient temperature is so buoyant, it needs to be blown downward from ceiling outlets to provide good air mixing and to avoid stagnation near the floor. Although the capability is there to have both heating and cooling air patterns from the same supply register, most homeowners either

don’t understand the concepts of air pattern adjustments or they don’t bother. My guess is the former in most cases because they have never been shown the advantages of adjusting air deflection to suit the seasonal demands. Since the blade setting has so much impact on performance, we have chosen a blade setting for general purpose cooling. The gap is specified at 13/32 of an inch for our data gathering purposes (it happened to be the width of the scale in my pocket at the time!). We show this dimensioned gap for the C series in our catalog. We did not choose to generate data at other blade settings due to resource constraints. This has proven to be acceptable based on my feedback. You may direct your questions, comments, or suggestions for future articles to me at any time. See our web site at www.hartandcooley.com for contact information.

CH1 adjustable CH2 adjustable

C3 adjustable C4 adjustable


TT-32 November 2006 Soft-Cone Flashings for Type B Gas Vent by Dave Fetters

Often I am asked if it is permissible to use a flexible pipe flashing to seal a roof penetration for our gas vent or chimney systems. The reason for the request is almost always because of “profiled” or metal corrugated roofing and decks. By “flexible pipe flashing” I mean the various brands of flashings that consist of flexible rubber cones attached to dead-soft, formable aluminum compression rings or bases. The rubber cones are usually designed in steps such that a single cone will accommodate several diameters of pipe. The soft aluminum base conforms to most roof panel configurations, if it is screwed down around the perimeter. These products were designed with the plumbing industry in mind, but the

usefulness of the design has caught the eye of the HVAC contractor as well. There are obvious advantages with using these flashings, and standing metal seam roof decking almost always demands their use. The soft rubber cone will flex for different roof pitches. The aluminum base will easily bend to fit most contours and is then sealed with silicone and

fastened tightly to the deck. The EPDM rubber used for the cone will withstand a 212ºF constant temperature—more than adequate for B-vent applications. For higher skin temperature resistance, an optional silicon rubber cone is usually available.


So my response is a cautionary “Yes, you may use it.” I immediately qualify my answer with a discussion about some issues that affect performance and acceptance by the building owner or mechanical inspector. Listing: Foremost is the fact that these flashings are not UL-listed for use with B-vent, and may not be acceptable to the authority having inspection jurisdiction. For the most part, my experience indicates that use with Type B gas vent is almost universally accepted by inspectors. However, these flashings shall not be used with our factory-built chimney system because of our UL-listing and associated performance requirements. I suspect all other chimney manufacturers’ systems have listed flashings that preclude the use of these unlisted flexible flashings. Sealing: Rubber cones have to be made to fit the pipe diameter by cutting or pulling tear-off rings. A tear-off will have a smoother sealing surface than a cut edge, which affects how well the cone seals to the pipe. The smoother and tighter it is, the better it will seal, since a storm collar is generally not used. However, no matter how well the cone might fit without sealant, water will find its way along the vertical lock seam on B-vent and run down the pipe. I encourage a little dab of silicone at that point to prevent water leakage. Temperature: As I’ve already indicated, EPDM rubber will withstand the skin temperature of B-vent connected to appropriate appliances without breaking down.

Our testing has shown that a B-vent skin temperature will not exceed about 200ºF measured near the appliance when the vent is fired at its maximum input temperature on a continuous basis. Cycling appli-ances with normally lower flue gas temperatures will not generate this much skin temperature, especially when measured near the termina-tion. Unlisted appliances or those not approved for use with B-vent may easily cause skin temperatures to exceed 212ºF, depending on the firing conditions. This will exceed the EPDM rubber maximum temperature. An option other than using a soft-cone flashing for profiled roofing systems is to build or purchase a custom roof curb with integral cricket, such as the Roof Products & Systems brand from Commercial Products Group in Bensenville, IL (800.624.8642 phone). This provides a smooth, flat surface to mount a factory-made flashing.


TT-33 December 2006 Condensation in Type B Gas Vent: Why It Forms and How to Prevent It

by Dave Fetters A recurring theme in my work is the question from many quarters about why condensation is occurring in a Type B gas vent and what to do about it. Unfortunately, the condensation usually drips out of an elbow in the attic, wets the insulation, and stains a bedroom ceiling before it is noticed elsewhere. Condensate will form in the coldest part of the vent (near the termination) when the flue gas cools to its dew point temperature. This is the temperature at which the flue gas, with its heavy load of moisture in the form of water vapor, starts to condense (“dew” forms) on the cooler walls of the vent. A 100,000-BTUH furnace burning for one hour will generate a gallon of water in the form of vapor in the flue gas. The vent, through proper design and sizing, must keep the moisture in the vapor state until it exits the vent. This is one reason why the

B vent sizing tables are so important! With the Department of Energy likely to increase efficiency requirements of gas-fired appliances by 2 percentage points in the

near future, adhering to the tables to prevent condensation becomes critical. The following is a list of reasons for condensate development in

the approximate order of priority, based on my experience. 1. Single-wall connectors used with 80%

appliances. It’s okay to use single-wall connectors with these non-draft hood-equipped appliances, IF one uses the proper sizing table. The FAN MIN input from the single-wall connector sizing table must be met or exceeded to prevent condensation. Be careful of 2-stage and modulating equipment. Use the lowest firing rate for determining FAN MIN.

The vent, through proper design and sizing, must keep the moisture in the

vapor state until it exits the vent. This is one reason why the B vent

sizing tables are so important!


2. Water heater connector is too small. In multiple-appliance systems, a 3-inch diameter connector will not accommo-date water heater inputs greater than about 35,000 BTUH, even though water heaters with inputs as high as 50,000 BTUH still use 3-inch draft hood collars. Use a 4-inch connector on every 3-inch water heater collar to eliminate this problem. Do not assume that because the water heater has a 3-inch draft hood collar that 3-inch connector is always appropriate.

3. Offsets (laterals, horizontal runs) in

connectors and common vents that are too long. A single-appliance vent sizing table provides data that tells you how far the horizontal run may be. However, for a multiple-appliance connector or for the common vent in multiple-appliance systems, the limit is 1½ feet of horizontal run per inch of connector or vent diameter. This can be a significant limitation, especially for common vents, but, if exceeded, leads directly to condensate formation.

4. Combustion and make-up air issues.

The code is very clear about how to calculate and provide proper openings for combustion and make-up air. These days with tight homes, larger bath fans, fancy cooking appliances, dryers, and decorative gas-fired appliances consuming indoor air, it becomes imperative to provide air for the heating appliances in the required amounts. Condensation is only one sign of restricted air. Spillage, no draft, and, in a worst case, carbon monoxide are other consequences.

5. The common vent is too small, too

large, or exposed on an outside wall. A common vent that is too small will obviously have to be made larger, have an appliance removed from the system, or be engineered to work. To prevent a common vent from being too large, its area shall not be more than 7 times the area of the smallest connected appli-ance collar. A vent shall not be exposed to the outdoors below the roofline. These are existing fuel gas code require-ments and have been for some time.

6. An interior masonry chimney venting 80% appliances. Neither single nor multiple fan-assisted 80% appliance(s) shall be vented into an interior masonry chimney without a dedicated relining system.

7. Venting into exterior masonry chim-

neys. Even though the National Fuel Gas Code has sizing tables for this scenario, they are very complicated and restrictive. The best choice, especially for the northern tier states, is to plan for and install a properly sized, listed gas appliance relining system approved for this use.

8. Not properly accommodating appli-

ances with vent dampers. An appliance with a built-in powered vent damper must be sized using NAT MAX in combination with FAN MIN from the sizing tables.

Insulating B vent to try to solve a con-densation problem will not work, and B vent manufacturers do not want their B vents insulated. The insulation is treating the symptom, not the problem. Although condensate formation may manifest itself in the vent extremities, the cause more often than not may be in the mechanical room. The Hart & Cooley Gas vent, chimney sizing & application guide has a lot of good information, which includes sizing tables and combustion air opening requirements. To receive a free copy, please contact your Customer Service Representation. Or, if you prefer, you can view the guide on our web site at www.hartandcooley.com.


TT-34 January 2007 Vent Offsets

by Dave Fetters A loyal reader of these Tech Talk newsletters suggested that I address vent offsets as a topic. Even though I have other Tech Talks already written and could have used for this month, this topic excited me and is a worthy subject for discussion. Only an engineer can get “excited” about such matters. Others are merely interested. The National Fuel Gas Code (NFGC) and International Fuel Gas Code are not explicit in their definitions of what constitutes an offset in a vent system. A typical definition of vent offset is this one from the NFGC (2006 edition) Paragraph 3.3.107: “Vent Offset. An arrangement of two or more fittings and pipe installed for the purpose of locating a vertical section of vent pipe in a different but parallel plane with respect to an adjacent section of vertical vent pipe.”

Notice that the definition avoids any mention of the angle or slope of the offset. However, buried in the text of the paragraphs of Chapter 13, where the code discusses sizing, is some insight into what angle the code refers to when it mentions lateral. Paragraph 13.1.3 for single-appliance venting says “…venting with lateral lengths include two 90° elbows.” Clearly, this statement means that a lateral is horizontal pipe between two 90° elbows. The horizontal offset is measured along this horizontal run from the same point on each end (centerline to centerline or outside wall to the same outside wall at the other end). The code also speaks about offsets that can be pipe-installed at angles less than 90° (30° or 45° from vertical for instance) as stated in paragraph 13.2.5


Vent Offsets and paragraph 13.2.6 Elbows in Vents. When a vent has an offset, say in an attic, where the angle of the offset is 45°, the code looks at what the vertical-centerline-to-vertical-centerline, horizontal displacement is, and uses that for the offset or lateral allowance. This is the dimension labeled “Offset” in the adjacent drawing. Typically, if the vent is for a single appliance, the sizing tables show the horizontal offset allowance in the column labeled “Lateral.” For multiple-appliance common vents, the code allows the horizontal offset to be no more than 18 inches for each inch of common vent diameter. For example, in the adjacent figure, the vent is tilted at approximately 45°, and we want to find the horizontal length labeled “Offset.” To determine this offset displacement, one would multiply the hypotenuse by the cosine of 45° (sorry). In layman’s language, take the running length of the pipe and multiply it by .7 (the cosine of 45°). So if the running length were 10 feet, the offset is 7 feet (.7 x 10). If the vent is offset 30° from vertical, then multiply the running length of pipe by .5 to get the offset (trust me on this one).

In summary, the NFGC allows offsets in single-appliance and multiple-appliance vents. The offset in the eyes of the code is the horizontal displacement of the vent. A horizontal vent may be measured directly. A vent on some angle can be calculated as demonstrated above, guessed at (bad idea), or measured using a plumb bob from the displaced vertical. Whew!


TT-35 February 2007 Wood vs. Metal Floor Diffusers

by Dave Fetters and Mark Walraven When considering the use of wood floor diffusers instead of the traditional metal kind, one should consider how they perform, as well as how they look. Wood floor diffusers can be an aesthetically pleasing addition to a home. Solid wood or wood-faced floor diffusers look nice, can be stained to match wood floors, and recessed flush with a wooden floor surface (R403).

However, when considering the use of wood floor diffusers instead of the traditional steel diffusers, one should also account for

changes in product performance. All Hart & Cooley floor diffusers (including wood) meet the International Mechanical Code for strength. Since wood is not as strong as steel, more wood must be used in the diffuser to meet the strength requirements. Consequently, wood diffusers generally have different performance character-istics than steel diffusers. Performance, for the purpose of this Tech Talk, refers to the effective area and throw pattern of the diffuser. For example, the R400 (the wood equivalent to the steel Hart & Cooley 421) has only 60% of the effective area of the 421. One must consider the impact that lower effective area (lower cfm delivery) will have on

421

R400

R403


room comfort before selecting the diffuser. A larger size wood diffuser or additional floor diffusers may be necessary to maintain the same cfm delivery as a traditional steel diffuser. An additional consideration is the diffuser’s throw pattern. A diffuser’s throw pattern affects room air mixing, and different diffusers have different fin angles and throw patterns. Most wood diffusers have parallel fins that deflect the air in two directions. Whereas the 421 and 411 fins are more vertical in the center, and they slope progressively as the fins approach the outside edges. This fan-shaped pattern helps diffuse (disperse and mix) the air better than the parallel fins of the wood register. Other decorative floor diffuser products have designs, such as a Victorian scroll pattern and a Contemporary “parallel blade” pattern. As the fin pattern changes, so does the throw pattern. So, be sure to match the correct decorative product to the application and environment. Engineering data for Hart & Cooley decorative registers can be found at our web site at www.hartandcooley.com.

Victorian

Contemporary


March 2007 Filter Grille Performance and Filter Limitations TT-36 by Dave Fetters Air circulation and conditioning usually incorporate some form of filtration of airborne particulate matter. There are many types of filtering mechanisms and methods, but I want to limit my remarks to the specific products we sell that allow air filtration. In our business, this air filtering is accomplished with a filter grille. The vast majority of our filter grilles are designed to use the readily available, 1-inch thick, cardboard-edged, disposable, fiberglass filters. Although we manufacture filter grilles that will accept thicker filters, relatively few are sold. Even though hog hair, foam, and other types of media filters may do a better job of filtration than the fiberglass, the universally available and inexpensive fiberglass filter is the most popular choice. These throwaway, one-inch panel filters are relatively inefficient and are effective with comparatively large particulate matter at low airflow rates

than other types of media and filtration methods. More important to the installer, most efficiency and pressure drop ratings are developed at only 300 feet-per-minute airflow velocity through the filter. The maximum airflow recommended is usually around 500 feet per minute, as published in the literature for these types of filters. Given the popularity of these types of filters, care must be given in selecting a filter grille size to accommodate the desired total CFM, while keeping in mind the filter limitations of velocity. Our recommendation for a maximum design face velocity is 400 feet per minute (FPM). To size a filter grille, look at the engineering data for that model. In the column less than 400 FPM, find a CFM number that is equal to or slightly higher than what is desired or required. The size corres-ponding to that rating is what should be used.


A rough but safe rule of thumb to use in the absence of available engineering data is to multiply the gross filter grille area in square inches by 2 CFM for each square inch. This will keep the face velocity below 400 FPM. For instance, if one thinks a 20 x 20 grille might be adequate, 20 x 20 = 400 gross square inches. Multiply this by 2 CFM per square inch and the result is a CFM of 800. Exceeding the filter’s capability will lower filtration efficiency by allowing some dirt to pass through and may dislodge particulate matter already captured if the face velocity becomes excessive. In addition, noise could become an issue with stamped-face filter grilles if velocities exceed about 500 FPM. T-bar filter grilles that are 2 x 2 in size are going to accept a nominal 20 x 20 filter. So, the rule-of-thumb CFM capacity will also be around 800 in order to maintain a 400 FPM face velocity. We build RHF45 filter grilles from as small as 6 x 6 to 48 x 48. This is a rigid filter grille with mullions and blade spacers at appropriate widths for added support. If one wanted to “push the envelope” for performance, this filter grille would handle higher velocities without fin or face vibration, which would occur with a stamped-faced filter grille like our 659 or 673. Obviously, the filter media would have to be up to the task as well. Our testing of a filter grille with and without a clean fiberglass filter has indicated that a clean filter reduces the performance data we publish by only about 3% to 5%.

Obviously, as a filter collects dirt, its resistance to flow increases and drives up the system pressure loss. For this reason, it is vitally important for a homeowner to establish a regular maintenance cycle to change out filters, so they do not affect the system performance.

RHF45 Aluminum Filter Grille

659 Steel Return Air Filter Grille

673 Steel Return Air Filter Grille

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