Where Is My Furnace Humidifier and How Do I Set It Up?

A whole-house humidifier is almost always attached to the furnace itself. Look at the large metal duct boxes directly above or beside the furnace, called the plenums, and you will usually find a small rectangular unit bolted to one of them, with a thin water line running to it and often a small drain tube.

The control that tells it what to do is a humidistat, a small dial or digital control that is often on the return duct or built into your thermostat. Once you know both pieces, setting it up for winter takes a few minutes.

Spotting the humidifier on your system

Start at the furnace and follow the ductwork upward. Bypass and fan-powered humidifiers are square or rectangular boxes with a round duct or a metal frame attached. Steam models look more like a small tank with a power cord. Nearly all of them have a saddle valve or a small copper or plastic tube bringing water from a nearby pipe.

If you cannot find anything, your home may simply not have one. Many homes in Pasco, Kennewick and Richland were built without a humidifier, and it can be added later. A technician can confirm in a minute or two whether one exists.

How the unit does its job

Most humidifiers use the furnace blower to move air across a wet water panel, a foam or mesh pad that sits in a stream of warm air. The air picks up moisture and carries it through the ducts to every room. The water panel needs a steady trickle of water, and the humidistat opens the water supply only when the house is drier than the target you set.

Because it depends on airflow, the humidifier only works while the furnace is running. On a mild afternoon when the heat barely cycles, the humidifier will add very little moisture, and that is normal.

Setting the humidistat

Most households do well with a winter target somewhere between 30 and 40 percent relative humidity. Go higher and you risk moisture collecting on cold surfaces. Go lower and you lose most of the comfort benefit.

• Mild winter days: set it near 40 percent.
• Cold snaps below freezing: drop it to around 30 to 35 percent.
• Very cold nights: consider 25 to 30 percent if you see fog or condensation on windows.
• Watch the corners of single-pane windows, since that is where too much moisture shows up first.

Lower the setting as the outdoor temperature falls, because cold glass cannot hold as much moisture as warm air. A cheap hygrometer from a hardware store lets you check the actual number rather than trusting the dial.

Why the right humidity feels warmer

Dry air pulls moisture off your skin quickly, which makes a room feel cooler than the thermostat says. Correct humidity slows that evaporation, so many people find they are comfortable a degree or two lower. The Tri-Cities has a dry climate to begin with, and a forced-air furnace dries the indoor air further, so winter mornings can feel parched.

What dry air does to a home and to you

Very dry air is hard on throats and sinuses, and many people notice static shocks, cracked lips and itchy skin. Wood floors, trim and furniture can shrink and open small gaps. Houseplants suffer too. Keeping humidity in a moderate range spares both the house and the people in it.

Keeping the humidifier healthy

The water panel is the part that needs attention. Hard water leaves mineral scale on it, and a scaled panel evaporates less and can grow slime if it stays damp. Replace the panel at least once a heating season, and shut the water supply off at the end of winter. Turn the humidistat down or off in summer so the unit is not running when the air conditioner is.

Check the drain line and water line for drips or crusty mineral trails. If the panel is heavily scaled, water is leaking, or the unit never seems to make a difference, call a professional instead of taking the unit apart while it is connected to water and power.

Air-Tech, the family-owned HVAC company on North Oregon Avenue in Pasco, can locate, service or add a humidifier as part of a heating checkup. Call (509) 392-2021 during office hours and ask for a visit before the cold settles in.