AHRI Guideline F 2008

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2008 Guideline for

Selection, Installationand Servicing ofResidential Humidifiers

AHRI Guideline F(formerly ARI Guideline F)


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Price $15.00 (M) $30.00 (NM)Printed in U.S.A.

Copyright 2008, by Air-Conditioning, Heating, and Refrigeration InstituteRegistered United States Patent and Trademark Office

IMPORTANT

SAFETY DISCLAIMER

AHRI does not set safety standards and does not certify or guarantee the safety of any products, components orsystems designed, tested, rated, installed or operated in accordance with this standard/guideline. It is strongly

recommended that products be designed, constructed, assembled, installed and operated in accordance withnationally recognized safety standards and code requirements appropriate for products covered by thisstandard/guideline.

AHRI uses its best efforts to develop standards/guidelines employing state-of-the-art and accepted industrypractices. AHRI does not certify or guarantee that any tests conducted under itsstandards/guidelines will be non-hazardous or free from risk.

Note:

This guideline supersedes ARI Guideline F-1997.


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TABLE OF CONTENTS

SECTION PAGE

Section 1. Purpose ......................................................................................................................................... 1

Section 2. Scope ............................................................................................................................................ 1

Section 3. Definitions .................................................................................................................................... 1

Section 4. Factors Affecting Humidification Load ....................................................................................... 2

Section 5. Humidification Load Determination ............................................................................................ 3

Section 6. Equipment Selection ..................................................................................................................... 5

Section 7. Installation Practices ..................................................................................................................... 7

Section 8. Servicing Practices ....................................................................................................................... 8

TABLES

Table 1. Humidification Load Required ...................................................................................................... 3

Table 2. Correction Factor for Other Indoor Temperatures and RH Conditions ........................................ 4

Table 3. Selection Based on Water Hardness ............................................................................................. 5

APPENDICES

Appendix A. References Normative ............................................................................................................... 9

Appendix B. References Informative ............................................................................................................. 9

Appendix C. Periodic Maintenance Checklist Informative .......................................................................... 10


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AHRI GUIDELINE F-2008 (formerly ARI GUIDELINE F-2008)

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SELECTION, INSTALLATION AND SERVICINGOF RESIDENTIAL HUMIDIFIERS

Section 1. Purpose

1.1 Purpose. The purpose of this guideline is to establish, for residential Humidifiers: definitions; factors affectingHumidification Loads; determination of Humidification Load; equipment selection; installation practices; and servicingpractices.

1.1.1 Intent. This guideline is intended for the guidance of the industry, including manufacturers, engineers,installers, contractors and users.

1.1.2 Review and Amendment. This guideline is subject to review and amendment as technology advances.

Section 2. Scope

2.1 Scope. This guideline applies to Central System and Self-Contained Humidifiers, as defined in AHRI Standards 610

and 620, installed in residential and small commercial applications.

Section 3. Definit ions

3.1 Definitions. All terms in this document follow the standard industry definitions in the current edition ofASHRAETerminology of Heating, Ventilation, Air-Conditioning and Refrigeration unless otherwise defined inthis section.

3.2 Humidifier. A device used to add moisture to the air.

3.2.1 Central System Humidifier. A class of Humidifier intended to discharge moisture into the air stream of acentral air system. It may be mounted in or on the following:

a. Return air ductb. Return air plenumc. Supply air ductd. Supply air plenume. By-pass (supply to return)f. Heating or cooling central air system

3.2.2 Self-Contained Humidifier for Residential Application (Self-Contained Humidifier). A class of Humidifierintended for non-ducted installation, but may be employed in ductwork to be installed with a water make-up lineand/or drain and electrical service independent of a central air system. It may or may not be installed within thehumidified space.

3.3 Humidification Capacity. The capacity associated with a Central System Humidifiers ability to add moisture to airexpressed in gal/day [L/day] of continuous operation.

3.4 Humidification Load. The amount of water discharged by the humidifier required to satisfy the conditionsdesired in the space gal/day [Liter/day].

3.5 Humidifier Types.

3.5.1 Atomizing (Centrifugal, Nozzle, Ultrasonic). A type of Humidifier intended for duct applications in whichwater is dispersed to air as a fine mist.

3.5.2 Heated Tank. A type of Humidifier which generates steam or evaporates water into the ductwork orconditioned space using an energy source.


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AHRI GUIDELINE F-2008 (former ly ARI GUIDELINE F-2008)

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3.5.3 Wetted Media. A type of Humidifier intended for duct applications in which water passes over media placedin the air stream. As the air passes through the wetted media, water evaporates increasing the moisture content of theair stream. The water not evaporated is drained, retained in the reservoir, or returned to a tank for recirculation.

3.6 Rating Conditions. Any set of operating conditions under which a single level of performance results and whichcauses only that level of performance to occur.

3.6.1 Standard Rating Conditions. Rating Conditions used as the basis of comparison for performancecharacteristics.

3.7 Should. Should isused to indicate provisions which are not mandatory butwhich are desirable as good practice.

3.8 Water Hardness. The presence of mineral solids (e.g., calcium, iron, magnesium, and sodium) that are naturallypresent in the water and are expressed as grains/gal [grams/Liter] or ppm.

3.8.1 Degrees of Water Hardness.

3.8.1.1 Hard Water. Unconditioned water with a dissolved solid content of 7.0 to 10.5 grains/gal [0.120 to0.180 grams/Liter] 120 to 180 ppm.

3.8.1.2 Moderate Hard Water. Unconditioned water with a dissolved solid content of 3.5 to less than 7.0grains/gal [0.060 to less than 0.120 grams/Liter] or 60 to less than 120 ppm.

3.8.1.3 Naturally Soft Water. Unconditioned water with a dissolved solid content usually below 3.5grains/gal [0.06 grams/Liter] or 60 ppm.

3.8.1.4 Very Hard Water. Unconditioned water gal/day [Litre/day] with a solid content of more than 10.5grains/gal [0.180 grams/Liter] or 180 ppm.

3.9 Water Types.

3.9.1 Demineralized Water. Water which is largely free from particles and dissolved substances having aconductivity below 0.2 micro-Siemens per centimeter (S/cm).

3.9.2 Softened Water. Water that has been conditioned by the ion exchange process (used widely in residentialtreatment) to exchange calcium and magnesium ions with sodium or potassium ions.

Section 4. Factors Affecting Humidi fication Load

4.1 General. The following should be used as a basis for estimating the Humidification Load required:

a. Outdoor design conditionsb. Indoor design conditionsc. Size and physical characteristics of residence

(1) Conditioned space volume(2) Tightness of structure, insulation, storm windows and doors or equivalent, etc.

(Note: Some older structures may have inadequate protection against water vapor transmission through walls,which may result in damage from excessive moisture.)

d. Quantity of outdoor air entering the conditioned space

(1) Mechanical and natural ventilation(2) Fireplace dampers (Open fireplace dampers greatly increase the amount of outdoor air added to the heated

volume of the structure. Satisfactory performance of a Humidifier, as applied to a given structure, is basedupon these dampers being closed.)


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e. Internal load generated

(1) In calculating humidity load requirements in residential applications, internal load factors are not includedbecause of the variation in living habits, e.g., bathing and laundry habits, cooking, number of occupants, etc.

4.1.1 Outdoor Design Conditions. The outdoor design conditions to be used for calculating humidity requirementsare 0.0F [-18C] to 20F [-6.7C] and 80% to 70% RH.

4.1.2 Indoor Design Conditions.1

5.1 Humidification Load requirements are determined from Table 1.

The indoor design conditions to be used for the calculation of humidityrequirements are 75 F [24 C] and 30% RH.

4.1.3 Ventilation. Ventilation in a residence is, in most current practices, handled by infiltration. Some installationsuse a positive inlet duct. For load estimates, calculate the infiltration and positive air quantity (if any) and add themtogether.

4.1.3.1 Infiltration. Infiltration may be estimated as follows:

a. For tight construction, use air change per hour.b. For average construction, use 1 air change per hour.c. For loose construction and/or maximum ventilation factor, use 1.5 air changes per hour.

TheASHRAE Handbook HVAC Systems and Equipmentdefines a tight house as one ...assumed to be well insulatedand to have vapor retarders, tight storm doors, windows with weather-stripping, and a dampered fireplace. An averagehouse is insulated and has vapor retarders, loose storm doors and windows, and a dampered fireplace. A loose house isgenerally one constructed before 1930 with little or no insulation, no storm doors, no insulated windows, no weather-stripping, no vapor retarders, and often a fireplace without an effective damper. Any air exhausted from or freshoutdoor air being introduced into the home will increase the Humidification Load.

Section 5. Humidif ication Load Determination

Table1. Humidifi cation Load Required, gal/day [L/day]

Type ofConstruction

Volume of Building ft3

[m3

(approximate)]

8,000 [227] 10,000 [282] 12,000 [340] 16,000 [453] 20,000 [566] 24,000 [680] 32,000 [906] 40,000 [1133]

Tight 4.3 [16] 5.3 [20] 6.4 [24] 8.5 [32] 10.6 [40.2] 12.7 [48.2] 17.0 [64.4] 21.2[80.4]

Average 8.6 [32] 10.6 [40.2] 12.8 [48.4] 17.0 [64.4] 21.3 [80.2] 25.4 [96.5] 34.0 [148] 42.6 [160]

Loose 12.7 [48.3] 15.9 [60.3] 19.1 [72.6] 25.5 [96.6] 31.8 [121] 38.1 [145] 51.0 [193] 63.6 [241]

Note:

Loads shown in the table are based on indoor conditions of 75F [24 C ] and 30% RH with 0.0F [-18C ] and 80% RH outdoors. An amount of 2.0 gallons per day [7.6 liters per day] may be deducted from these figures if it is desired to take credit for internal sources of

moisture (based on a family of four).

1 Obtained from Standard Rating Conditions of AHRI Standards 610 and 620.


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Table 2. Correction Factor fo r Other Indoor Temperatures andRH Conditions.

Temperature

Indoors.

70F[21 C]

75F[24 C]

Indoor % RH 30% 35% 40% 30% 35% 40%

Correction Factor 0.8 1.0 1.3 1.0 1.2 1.4

Note: This table provides the correction factor to use for other indoor temperatures and RH conditions.Multiply Humidification Load Required from Table 1 by the appropriate correction factor in Table 2.

5.2 If it is desired to calculate the Humidification Load for any reason, such as for buildings of unusual design, thefollowing equation will be used:

Calculate the indoor conditioned volume of the building.

V = (width) (length) (height) 1

daypergallonsLoad,tionHumidifica33,082

G)(V)(R)(

))()((

G)(D)(V)(R)(

=+

=+

= LSLSa 2

=+

=+

= dayperLitersLoad,tionHumidifica

35.33

G)(V)(R)(

))()((

G)(D)(V)(R)(LSLS

a

Where:

a = Conversion factor, 7,000 grains/lb [1,000 grams/kg]D = 24 hours/dayG1 = Moisture content of air at indoor design conditions (See 4.1.2) grains/lb [grams/kg]

G2 = Moisture content of air at outdoor design conditions (See 4.1.1) grains/lb [grams/kg]H = Humidification Load requirement, in gal/day [L/day]L = other moisture losses, gal/ dayR = Calculated air changes per hourS = contribution of internal moisture sources, gal/dayV = Total indoor conditioned volume of space being humidified, ft3 [m3]G = Difference in moisture content of air between indoor and outdoor design conditions, grains/lb [grams/kg] of dry

air (See 4.1.1, 4.1.2 and 5.2.1 step 4.) = Density of water, 8.34 lb/gal of water [1.00 kg/L of water] = Specific volume of moist air at indoor design conditions = 13.6 ft3 per lb of dry air [0.848 m3/kg of dry air]

5.2.1 Example.

1. Space being humidified (volume of the building):V = 40.0 ft [12.2 m] wide 50.0 ft [15.2 m] long 8.0 ft [2.4 m] high = 16,000 ft3 [453.1 m3]

2. Air changes per hour (tight construction) = 1/2 (See 4.1.3.1)3. Assume S=L=0,4. G1 (indoor) at 75F [24C] & 30% RH = 39 grains/lb dry air [5.6 grams/kg dry air] (See 4.1.2.)

G2 (outdoor) at 0.0F [-18C] & 80% RH = 4 grains/lb dry air [0.6 grams/kg dry air] (See 4.1.1.)G = G1 (indoor) - G2 (outdoor) = 35 grains/lb dry air [5.0 grams/kg dry air]

Note: Values of the air moisture contents G1 & G2 are obtained from a psychometric chart.5. If the indoor room conditions were 75 F & 40% RH, then from Table 2, the correction factor is 1.4.

Thus, the corrected humidification load requirement is 8.5x1.4 = 11.9 gal/day [32x1.4=44.8 L/day]


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6. Humidification load requirement =

gal/day5.8(35)(0.5)(16,000)(24)

))()((

G)((R)(V)(D)

(8.34)(13.6)(7,000)==

a

==

L/day0.32(5.0)(0.5)(453.1)(24)

))()((G)((R)(V)(D)

(1.0)(0.848)(1,000)a

5.3 When additional outside air is being introduced into the home using devices such as fresh air systems, exhaust fans, oropen fireplace dampers, additional humidification may be required. Equation 3 will assist in this calculation.

Determine amount of outside air being introduced per hour.

Using the Equation 1 determine the additional Humidification Load.

gal/day6.4

(8.34)(13.6)(7,000)

(35)(6,000)(24)

))()((

G)((OAV)(D)==

a

3

= L/day24.0

(1.0)(0.848)(1,000)

(5.0)(169.92)(24)

Where OAV = Outside Air Volume = (100 cfm of device)(60 minutes) = 6,000 cfh (cubic feet per hour) [170 m3/h(approximate)].

Add results of Equation 2 and 3, for the total Humidification Load.

9.78+6.4 = 16.18 gal/day[36.8 + 24.0 = 60.8 L/day]

Section 6. Equipment Selection

6.1 Types. Select equipment which is suitable for use with the existing or proposed heating system: i.e., Central SystemHumidifier or Self-Contained Humidifier.

6.2 Water Conditions. Select the class of Humidifier which will operate satisfactorily with a minimum of maintenanceusing the types of water supply available, as shown in Table 3. (See 3.5 and 3.9)

Types of

Humidifiers

Table 3. Selection Based on Water Hardness

DemineralizedWater* NaturallySoft Water SoftenedWater*

Moderate

HardWater

Hard Water Very HardWater**

Atomizing X X --- --- --- ---

WettedMedia

X X X X X X

Heated Tank X X X X X X

* Humidifier construction should use non-corrodible components.** Excessive water hardness can increase maintenance requirements of Humidifiers.


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6.3 Limitations.

6.3.1 In all cases, equipment should be used only within the recommended limitations specified by themanufacturer except where specific approval for deviation is obtained from the manufacturer.

6.3.2 Services available, i.e., electricity, water, drain, physical layout, space available, accessibility for service, etc.,may further limit the selection of equipment.

6.4 CapacityAdjustments.

6.4.1 Central System Humidifiers.

6.4.1.1 The ANSI/AHRI Standard 610 rated capacity should be corrected to the actual capacity to berealized in a given system by the following method:

a. Adjust to reflect actual amount of time the system operates (usually 75% of total time, but thiscan vary based on heating equipment selected) to maintain the temperature desired in thespace when minimum outside design temperatures exist.

Note: Humidifiers may turn on the system air mover when an increase in humidity is required.

b. Adjust to reflect actual temperature of the air passing into the evaporative equipment whensuch temperature is other than that used in the standard rating. (See manufacturersspecifications.)

c. Adjust to reflect actual static pressure differential from supply to return side of the systemwhen such differential is other than the 0.20 in H2O [50 Pa] used in the standard rating andselect the evaporative equipment utilizing this method of inducing airflow through theHumidifier. (See manufacturers specifications.)

d. Adjust to reflect the velocity of airflow through the system when such differs from the 800ft/min [4 m/s] used in the standard rating. (See manufacturers specifications.)

e. Adjust to reflect any other deviation from AHRI Standard Rating Conditions specifically

required by the manufacturers published literature, i.e., water pressure, etc. (Seemanufacturers specifications.)

f. Adjust to reflect supplementary water temperature to be used when that temperature is otherthan the temperature used in the standard rating. (See manufacturer's specifications.)

6.4.2 Self-Contained Humidifiers.

6.4.2.1 The ANSI/AHRI Standard 620 rated capacity to satisfy the demand load calculated should becorrected to the actual capacity to be realized from the equipment by the following method:

a. Adjust to reflect supplementary water temperature to be used when that temperature is otherthan the temperature used in the standard rating. (See manufacturers specifications.)

b. Adjust to reflect any other deviation from AHRI Standard Rating Conditions specificallyrequired by the manufacturers published literature, i.e., water pressure, etc. (Seemanufacturers specifications.)

6.5 Accessory Selection.

6.5.1 Humidistat. Manufacturers recommendations should be followed to obtain optimum performance and toavoid possible problems.

6.5.1.1 A humidistat control is recommended to prevent the possibility of over humidification.


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6.5.1.2 A humidistat control should be used when any Central System Humidifier is selected for use on asystem to be operated on constant air circulation.

6.5.1.3 A humidistat control should be used when any type Humidifier is selected that has a correctedcapacity rating under actual operating conditions that exceeds the demand load calculated.

6.5.2 Other Accessories. Re-circulating pumps, valves, etc. should be selected as recommended by themanufacturer of the Humidifier selected.

6.6 Building Codes. Equipment should be selected to meet all pertinent local, state, or national codes. This applies toHumidifiers, humidistats, and other accessory items.

Section 7. Installation Practices

7.1 General. A satisfactory humidifier installation depends upon the use of diligence in utilizing good installationpractices. It should be kept in mind that every customer has definite expectations for performance and serviceability of theunit; and if these conditions are met, the result will be a satisfactory installation. A constant awareness of these points willguide the installer to making good detailed decisions as the installation progresses.

7.1.1 Cleaning. Although this section is primarily concerned with installation of the unit, the installer must keep in

mind that when a Humidifier atomizes or evaporates water a residue will accumulate necessitating regularmaintenance for cleaning. Serviceability must be as easy as possible and is greatly affected by the installation methods.

7.1.2 Manufacturers Instructions. Humidifier manufacturers supply installation instructions with the units which,should be carefully followed and supplemented by this standard as required.

7.2 Installer Familiarization. The installer should familiarize himself with the product, taking particular note of thehumidifier's components. Electrical parts may need to be inspected or replaced should be readily accessible.

7.3 Location. The location of a Humidifier for use in existing heating systems is usually determined at the job site.Manufacturers installation instructions usually provide sketches showing typical mounting arrangements on duct systems.Installing a Humidifier on existing ductwork may dislodge dust and dirt; therefore, vacuum-clean through the mounting holein the area of humidifier installation. In new systems, future construction and basement finishing must be considered and

ample access must be reserved for the maintenance and service of the Humidifier.

7.3.1 Outdoor Installation. Most Humidifiers are intended for installation indoors and, unless the manufacturersinstructions specifically allow unheated area installation, assume indoor heated location only.

7.3.2 Prevention of Water Damage. If the Humidifier is located in or above finished space such that an accidentaloverflow may damage floors, carpets, wall finishes, etc. a means should be provided to prevent damage in the eventoverflows occurs. If the Humidifier has no provisions for connecting an overflow drain, a drain pan with a drain hoseshould be installed beneath the Humidifier.

7.4 Electrical Connections. It should be noted that many Humidifiers are designed to be connected to a separatelyprotected circuit or internally in the air-handler (See manufacturers installation guidelines).

A means for disconnecting the line power supply to the Humidifier should be provided. All wiring should conform to local,state, and national codes.

7.4.1 It may be necessary to wire steam generating units with time delay relays or temperature switches so whenthe Humidifier is turned off, the furnace blower continues to carry away the residual steam until the water is cooled.

7.4.2 It may be necessary to wire steam generating units and atomizing units with an airflow switch or an electriccurrent sensor relay to turn the Humidifier off if airflow in the air handling system is interrupted (see manufacturersinstallation guidelines).


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7.5 Start-Up and Check-Out. After installation is completed, operate the total system through several complete cycles ofevents, preferably with a system thermostat and humidistat, if installed. Observe for normal operation as recommended bymanufacturer.

Following the running of several complete cycles of events, set the thermostat system switch, temperature selector andhumidistat at customers desired settings. It is also wise to have the customer perform all steps for familiarization. Beforeleaving the premises, review the owners manual with the customer.

7.6 Customer Education. THIS CAN BE THE MOST IMPORTANT STEP IN THE INSTALLATION. Explain to thecustomer what to expect from the Humidifier. Also, instruct the customer in the proper cleaning and operation in order toinstill self-confidence and make them aware of any precautions while doing this.

Explain anything that they may later see or hear to prevent anxiety or dissatisfaction, such as condensation on windows,normal mineral buildup, normal operating sounds, etc. Mention that there may be a time lag before the set humidity level isachieved.

Also indicate the advantages of humidification which they will enjoy and be sure to explain that limitations imposed by thestructure will determine the level of humidity which can be maintained. Also, teach the customer how and when to adjust thehumidistat for various ranges of outdoor temperatures.

Section 8. Servicing Practices

8.1 Regular Care and Servicing. Humidifiers require periodic maintenance and servicing either by the user or competentservice personnel to provide continued customer satisfaction, longer equipment life and a reduction in emergency servicecalls, resulting in lower annual cost to the customer.

8.2 Periodic Maintenance Check List. Appendix C contains an example of a check list for use by the user or servicepersonnel. This type of check list is a result of extensive use in the field by many service organizations and reflects theirsuggestions. There are two advantages to using a check list. First, it helps the service person to develop an efficient routine;and second, gives the service technician an outline of service that can be reviewed by the owner.

8.3 Special Maintenance Considerations. Humidifier designs are of three basic types: Atomizing, Wetted Media andHeated Tank. Depending upon the particular design of the Humidifier, there are usually special maintenance routines which

must be followed regularly in order to insure continued performance of the unit. Since these routines will vary, it isparticularly important that the customer be familiar with any special maintenance considerations by studying the materialsupplied with the Humidifier.

For new installations, the Humidifier should be inspected monthly to determine a proper maintenance schedule.


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APPENDIX A. REFERENCES NORMATIVE

None.

APPENDIX B. REFERENCES INFORMATIVE

B1 Listed here are standards, handbooks and other publications which may provide useful information and backgroundbut are not considered essential. References in this appendix are not considered part of the guideline.

B1.1 ANSI/AHRI Standard 610-2004 (formerly ANSI/ARI Standard 610-2004), Performance Rating of CentralSystem Humidifiers for Residential Applications, 2004, Air-Conditioning, Heating, and Refrigeration Institute, 2111Wilson Boulevard, Suite 500, Arlington, VA, 22201, U.S.A.

B1.2 ANSI/AHRI Standard 620-2004 (formerly ANSI/ARI Standard 610-2004), Performance Rating of Self-Contained Humidifiers for Residential Applications, 2004, Air-Conditioning, Heating, and Refrigeration Institute,2111 Wilson Boulevard, Suite 500, Arlington, VA, 22201, U.S.A.

B1.3 ASHRAE Handbook - 2008 HVAC Systems and Equipment, Chapter 21, Humidifiers, 2008, American Societyof Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, N.E., Atlanta, GA 30329, U.S.A.

B1.4 ASHRAE Terminology of Heating, Ventilation, Air Conditioning & Refrigeration, 1991, Second Edition,American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 1791 Tullie Circle, N.E., Atlanta,GA 30329, U.S.A.

B1.5 Brochure titledFacts about Humidifiers and MoldProperly controlled humidity does not promote moldgrowth, Air-Conditioning, Heating, and Refrigeration Institute, 2111 Wilson Boulevard, Suite 500, Arlington, VA,22201, U.S.A.


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APPENDIX C. PERIODIC MAINTENANCE CHECKLIST INFORMATIVE

PREVENTIVE MAINTENANCE AND SERVICE CHECK L IST FOR HUMIDIFIERS

Customer Name: Address:

Equipment Location: Contract Number:

Date Last Inspected: Date This Inspection:

Inspected By (Company, Address and Technician):

Humidifier Information

Manufacturer: Model Number:

When necessary, inspect, check, clean and adjust all items listed below:

WETTED MEDIA OR ATOMIZER ........................................................................................................................ Clean or replace media, filters and flow restrictors, as required, or clean all parts, if atomizing.

HEATED TANK ...................................................................................................................................................... Replace or clean cylinder parts Replace or clean immersion heater Clean the water tank and reservoir

SUMP AND DRAIN LINES .....................................................................................................................................Clean sump and drain lines. Make sure drains and drain lines are free of restrictions and have a constant downwardslope. If installed, check the drain pump for proper operation. Check for leaks and proper water level.

FANS AND MOTORS ............................................................................................................................................. Check fan set-screw for tightness. Check fan for deterioration and balance. Lubricate motor bearings as required.

CONTROLS ............................................................................................................................................................. Check operation of the disconnect switch. Check all electrical terminals for tightness. Check water flow controls for proper operation. Check humidistat for proper operation.

Key: - OK, X - Need Additional Service, - Repair or Replace

Remarks:


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