All images and data courtesy of Aprilaire.

Figure 1 Refer to Figure 2 to cross-reference these model numbers to model type.w w w . r s e s j o u r n a l . c o m16 RSES Journal DECEMBER 2013

One manufacturer’s approach to providing the right humidification solution with the heating systems in the field today.

Humidification SyStemSProPerly matcHing

To those in the HVACR industry, humidification is a common-sense approach to providing a customer with whole-home comfort. However, when it comes to selling one of these systems, contractors/technicians need to have a game plan. A strategy that addresses both common sense and the science of hu-midification along with what that means for human comfort. In addition to offer-ing up a list of physical symptoms that define an under-humidified home—including dry nose, cracked/itchy skin, sore throats, aggravated allergy/asthma symptoms and painful electric shocks—try incorporating

HVAC Variables Climate Zone/Recommended Solution by Model

Equipment TypePlenum Temp (°F)

Runtime Air-flow VolumeMidwest/Northeast

Mid-Atlantic/Mid-Southern South

Desert (Southwest) Mountain

Gas/Oil Furnace Single Speed 120–140 Periodic Adequate 1/2/3/4/5 2/3/4/5 3/4/5 5 3/4/5

Gas/Oil Variable Speed Furnace 120–140 Constant Limited 4/5 4/5 4/5 5 4/5

Heat Pump/GEO Single Stage 90 Periodic Adequate 3/4/5 3/4/5 5 5 3/4/5

Heat Pump/GEO Multi-variable speed furnace 90 Constant Limited 4/5 4/5 5 5 4/5

Boiler with AHU 70 Periodic Adequate 5 5 5 5 5Boiler with AHU/Coil 90 Periodic Adequate 4/5 4/5 5 5 5

Boiler NA NA NA 6 6 6 6 6

Electric Baseboard Heating NA NA NA 6 6 6 6 6

Humidifying with A/C Unit

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home issues that are also symptoms of this common winter-time problem, including chipping paint/plaster and splitting or cracked wood floors, fur-niture, trim and molding, etc.

If this is not enough to convince a homeowner of the importance of whole-home humidification, using statistics such as those reported by medical experts, including the fact that viruses thrive in low humidity, increas-ing the likelihood of catching colds, flu and upper respiratory ailments or the fact that overly dry environments make people more susceptible to infection, may earn their business.

The bottom line though, once a system has been sold, it is up to the contractor/technician to know how to properly match a humidification system with the type of heating system a hom-eowner has installed.

How it worksA whole-house humidifier is installed directly to the central new or exist-ing heating and cooling system. Hu-midity is introduced into the home’s air in the form of water vapor, which prevents minerals from entering the air in the home and potentially into the homeowner’s lungs. Water is sup-plied to a distribution tray, allowing it to flow evenly across a water panel. The resulting humidified air is then distributed via the heating and cool-ing system ductwork throughout the home. The important considerations in the evaluation of a humidifier are precise control, sufficient capacity, trouble-free performance and mini-mum maintenance.

Humidifiers can be installed on many different types of HVAC equipment and controlled to provide

Using a psychrometric chart, contractors/technicians can figure how much moisture needs to be added via a humidifier in order to make a home comfortable for its occupants.

w w w . r s e s j o u r n a l . c o m18 RSES Journal DECEMBER 2013

Humidifier Specifications

Model (type of equipment) A. Unit Size (in.)B. Plenum Opening (in.)Capacity

(gallons per day, gpd) Electrical Data

1 (Bypass unit—Uses 100% of water and evaporative technology that eliminates the

need for a drain.)

A. 15-3/8 W x 15-3/4 H x 10-1/4 D 6-in. diameter round openingB. 10 W x 12-3/4 H

17 gpd 24 V-60 Hz0.5 A

NOTE: This model can be installed in heat-pump applications. However, due to the fact that heat pumps deliver lower

temperature air to the home than gas furnaces, evaporation will be approximately 60% of rated capacity.

2 (Bypass unit—Designed for smaller homes.)

A. 15-5/8 W x 13 H x 10-1/4 D 6-in. diameter round openingB. 9-1/2 W x 91/2 H

12 gpd 24 V-60 Hz0.5 A

3 (Bypass unit—Uses the furnace blower to move air through a water panel evaporator.)

A. 15-3/8 W x 15-3/4 H x 10-1/4 D 6-in. diameter round openingB. 10 W x 12-3/4 H

17 gpd 24 V-60 Hz0.5 A

4 (Powered unit—Built-in fan that pulls heat-ed air directly from the furnace.)

A. 15-29/32 W x 18 H x10-11/32DB. 14-3/4 W x 14-5/16 H 18 gpd

120 V–60 Hz0.8 A

5 (Steam humidifier—For applications when evaporative units are less practical, attics,

crawl spaces, closets, milder winter cli-mates, non-forced air heating source.)

A. 10-1/8 W x 20-7/8 H x 7-1/8 DB. NA

11.5 gpd16.0 gpd20.5 gpd

120 V-60 Hz11.5 A

120 V-60 Hz16 A

208 V-60 Hz11.5 A

6 (Ductless humidification system includes model 5, fan pack, control and drain trap.)

Fan Pack:A. 14 W x 6-7/8 H x 5 D Finished grille 17-1/16 W x 7-13/16 HB. NA

30.0 gpd23.3 gpd34.6 gpd

208 V-60 Hz16 A

240 V-60 Hz11.5A

240 V-60 Hz16 A

Humidifier Sizing Chart (8-ft Ceilings)

Structure Tightness 1,000 sq ft 1,500 sq ft 2,000 sq ft 2,500 sq ft 3,000 sq ft 4,000 sq ft 5,000 sq ftHumidity needed (gpd per AHRI, Guideline F)

Tight 4.3 6.4 8.5 10.6 12.7 17 21.2Average 8.6 12.8 17 21.3 25.4 34 42.6Loose 12.7 19.1 25.5 31.8 38.1 51 63.6

optimal humidity levels. The information contained herein is based on an application guide provided by Aprilaire, which is meant to assist in the selection of the appropriate product based upon geography and type of heating equipment.

The product portfolio discussed here consists of evapo-rative flow through, fan-powered products and residential steam. It is important to consider the plenum temperature, air flow (fan speed) and runtime (heat call primary, fan only call secondary) when selecting products.

The variablesSeveral variables need to be taken into account before selecting a humidifier. Figure 1 breaks down several of these factors by climate/zone and the type of HVAC equipment (plenum temperature, run time, air-flow volume) in the home. Figure 2 offers the humidifier specs (unit size, plenum opening, capacity and electrical data) recommended in Figure 1. The data pre-sented is based on the AHRI Humidifier Sizing Chart (8-ft ceil-ings) Guideline F, which is available as a reference in Figure 3.

• A family of four will add 2 gal of humidity per day through everyday activities like breathing, cooking, bathing and washing. • Evaporative capacities assume blower is active 100% of the time, plenum temperature is at 120°F and water is cold.

Figure 2

Figure 3

DECEMBER 2013 RSES Journal 19w w w . r s e s j o u r n a l . c o mCircle Reader Service No. 65

Humidifier Specifications

Model (type of equipment) A. Unit Size (in.)B. Plenum Opening (in.)Capacity

(gallons per day, gpd) Electrical Data

1 (Bypass unit—Uses 100% of water and evaporative technology that eliminates the

need for a drain.)

A. 15-3/8 W x 15-3/4 H x 10-1/4 D 6-in. diameter round openingB. 10 W x 12-3/4 H

17 gpd 24 V-60 Hz0.5 A

NOTE: This model can be installed in heat-pump applications. However, due to the fact that heat pumps deliver lower

temperature air to the home than gas furnaces, evaporation will be approximately 60% of rated capacity.

2 (Bypass unit—Designed for smaller homes.)

A. 15-5/8 W x 13 H x 10-1/4 D 6-in. diameter round openingB. 9-1/2 W x 91/2 H

12 gpd 24 V-60 Hz0.5 A

3 (Bypass unit—Uses the furnace blower to move air through a water panel evaporator.)

A. 15-3/8 W x 15-3/4 H x 10-1/4 D 6-in. diameter round openingB. 10 W x 12-3/4 H

17 gpd 24 V-60 Hz0.5 A

4 (Powered unit—Built-in fan that pulls heat-ed air directly from the furnace.)

A. 15-29/32 W x 18 H x10-11/32DB. 14-3/4 W x 14-5/16 H 18 gpd

120 V–60 Hz0.8 A

5 (Steam humidifier—For applications when evaporative units are less practical, attics,

crawl spaces, closets, milder winter cli-mates, non-forced air heating source.)

A. 10-1/8 W x 20-7/8 H x 7-1/8 DB. NA

11.5 gpd16.0 gpd20.5 gpd

120 V-60 Hz11.5 A

120 V-60 Hz16 A

208 V-60 Hz11.5 A

6 (Ductless humidification system includes model 5, fan pack, control and drain trap.)

Fan Pack:A. 14 W x 6-7/8 H x 5 D Finished grille 17-1/16 W x 7-13/16 HB. NA

30.0 gpd23.3 gpd34.6 gpd

208 V-60 Hz16 A

240 V-60 Hz11.5A

240 V-60 Hz16 A

This control strategy will maximize the humidifier runtime/capacity. The automatic humidity controls have an integrated blower activation relay. This relay is factory set to on. It will turn on the humidifier and the HVAC blower for humidifi-cation without a heat call. This will dramatically increase the capacity of the humidifier. Installations with a manual humidifier control can in-crease capacity by turning the ther-mostat fan to on. This is not an option in the Desert (Southwest). When installing evaporative hu-midifiers, it is recommended they are plumbed to hot water. In the Midwest/Northeast cold water is optional.

Understanding all of the variables that goes into humidifying a home—from owner concerns and comfort desires to equipment matching and regional considerations—all play im-portant roles in the proper installation of system. While this article focused on one manufacturer’s approach, it is important for contractors and techni-cians to work with the dealers after having collected all these variables to provide a proper humidification solu-tion to the customer.

[Editor’s Note: Check out the manu-facturer’s original regional application guideline, which shows the actual model type and number for each application, by clicking here.]

Since its inception in 1938, Aprilaire has been designing, manufacturing and distributing comfort products, includ-ing humidifiers, to improve the indoor air of homes and businesses throughout North America. Aprilaire works close-ly with industry associations, such as AHRI and ASHRAE, to remain on top of industry standards and testing proce-dures. For more information, visit www.aprilairepartners.com.