The short answer
Bypass and fan-powered humidifiers are the most common furnace add-ons; steam units cost more but deliver the most moisture and work without the furnace heating. Plan on professional installation and a new water panel each heating season.
What installation involves
- Mounting the unit on the supply or return duct, and a bypass duct for bypass models.
- A cold or hot water supply line and a saddle or tee valve.
- A drain line to a floor drain or condensate pump.
- Low-voltage wiring to the furnace and a humidistat or compatible thermostat.
Because it involves plumbing, electrical and ductwork, most homeowners have a heating contractor install it.
Types
| Type | How it works | Best for |
|---|---|---|
| Bypass | Furnace blower pushes air through a wet panel via a bypass duct | Most homes with room for the duct |
| Fan-powered | Its own fan; no bypass duct | Larger homes, tight spaces |
| Steam | Electrode or element boils water | Very dry climates, heat pumps, high output |
Upkeep
Replace the water panel at least once a heating season, check the drain each fall, and turn the water supply off for summer.
Products mentioned
Questions readers ask
Does a whole-house humidifier work with a heat pump?
Yes, but heat pumps deliver cooler air, so evaporative units put out less; steam units suit heat pumps best.
How often do I change the water panel?
At least once a heating season, more often with hard water.