Home Projects Tips & Techniques How to Install a Whole-house Humidifier

How to Install a Whole-house Humidifier


Humidifiers improve the comfort of your home by adding moisture to the air. Typically, whole-house humidifiers are attached to the furnace in forced-air systems and are tied into the water supply and drain systems. Whole-house humidifiers can be manual or automatic. Manual models are cheaper, but they require monitoring of humidity levels and user adjustment. Automatic models have sensors that gauge the amount of humidity in the air and adjust moisture levels accordingly. Unlike earlier models, today’s humidifiers distribute water on demand, so you don’t need to be concerned about mold growth in the water reservoir.

Whole-house HumidifierMost home humidifiers are one of two types: drum-style and drip-style. A drum-style humidifier has a rotating drum fitted with an absorbent filter. The drum rotates and constantly picks up water from a reservoir. Air entering the furnace passes through the drum and carries water vapor into the heating system. A float controls the water level in the reservoir. In a drip-style humidifier, fresh water flows into a distribution tray and trickles through an evaporative pad filter. Any moisture that’s not carried away by air flowing through the pad drains into a drain tube.

Drum-style units are generally cheaper but require more maintenance. They use water more efficiently. Either style requires regular inspection.

Some humidifiers are installed on the return-air side of the furnace and humidified unheated air that passes into the furnace, which then heats and distributes it. Other humidifiers direct heated air through the filter by way of a bypass duct, which redirects heated air from the furnace back into the return-air duct to aid in evaporation. A third style employs a fan that runs independently of the furnace blower. This type is installed on the hot-air side of the furnace and does not bypass back to the return-air side.

Installing a whole-house humidifier is a relatively easy task if you have a forced-air heating system. Installation requires tying into the ductwork as well as the water supply and drain systems.

The humidifier unit comes with templates that you attach to the ductwork as guides for making cutouts for the main evaporator unit and the humidistat. The humidistat is an electronic gauge that measures air humidity levels and controls the humidifier output.

Although installing a central humidifier is not difficult, equipment manufacturers prefer that you hire a professional installer for the job. Be aware that choosing to do the work yourself may affect your warranty.

How to Install a Whole-house Humidifier Step 1: Turn off the furnace and central air conditioner. Trace the manufacturer’s template for the main humidifier unit onto the duct, according to the instructions. If the humidifier is a direct drum or bypass drip model, the main unit is installed on the cold-air side; if it has an independent fan, it is installed on the hot-air side. Drill a starter hole, and then cut the opening for the unit with aviator’s snips.

How to Install a Whole-house Humidifier Step 2: Secure the main humidifier unit (or the housing for it, on some models) in the opening with sheet metal screws.

How to Install a Whole-house Humidifier Step 3: If your humidifier unit has a bypass vent, make a cutout for the 6″-dia. vent pipe in the hot-air plenum, according to the manufacturer’s specifications.

How to Install a Whole-house Humidifier Step 4: Install a collar in the round cutout, then run vent pipe for the bypass, securing the connections with sheet metal screws.

How to Install a Whole-house Humidifier Step 5: Position and install the humidistat as directed by the manufacturer (normally, it is attached on the cold-air plenum near the furnace burner).

How to Install a Whole-house Humidifier Step 6: Connect the humidistat to the furnace. Most humidifiers are connected to the accessory panel on your furnace controls so they automatically turn on whenever the furnace blower cycles on. Note that some humidifiers run off of low-voltage power and may use a transformer to step down the voltage from the accessory panel.

How to Install a Whole-house Humidifier Step 7: Connect the solenoid. Connect the leads from the humidistat to the contacts on the solenoid valve, located on the humidifier unit.

How to Install a Whole-house Humidifier Step 8: Tap into a nearby water supply line (hot is preferable but not essential) with a saddle valve (if local code allows) or a T-fitting. Run supply tubing to the solenoid valve, and connect the supply tubing with a compression fitting. If your humidifier has a drain tube, run it to a drain opening as recommended by the manufacturer. Some units do not have a drain line because they automatically evaporate any excess water into the heating system. Install the filter, and test the system.


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