Guide · Home care

Furnace Humidifiers

A plain, friendly guide to the whole house humidifier that sits on some furnaces: what it does, the simple seasonal switch, and which jobs belong to the owner or a pro.

Start the checklist

Where to start

Air feels bone dry this winter?
Check the damper is on WINTER and the humidistat is on. See the seasonal switch.
Water dripping near the furnace?
Turn the humidistat to OFF and share a photo with your owner right away. See if something goes wrong.
New to this home?
Ask whether the furnace has a humidifier and who changes the pad. Then tick through the checklist.

The short version

Some forced air furnaces have a humidifier mounted right on the ductwork. In winter, heating dries the air out. A little added moisture can help with dry noses, static shocks and wood floors that shrink and gap.

It works through a water pad, sometimes called a water panel. Minerals in the water build up on it, so it needs a fresh one about once a heating season, or as often as the maker says.

Many models have a damper with a lever marked SUMMER and WINTER. Open for heating, closed when the air conditioning runs.

The water line, valves and fittings belong to the owner or a heating pro. When in doubt, share it.

Who does what

Every home and lease is a little different, so these are examples. When you are not sure, ask first.

Residents can often

Set the humidistat for the season
Switch the damper lever with the seasons, if your owner is fine with it
Look for drips, crust or a musty smell and report them
Keep the area around the furnace clear

Leave to the owner or a pro

Changing the water pad, unless your owner has shown you how
Cleaning the small brass water fitting and the electric water valve
Anything that needs a wrench on the water line
Clearing or rerouting the drain hose

The seasonal switch

In fall, when the heat comes on, move the damper lever to WINTER, which is open. Warm air from the furnace then passes through the wet pad and carries moisture through the home.
Set the humidistat to the level your owner or the maker suggests.
In spring, before the air conditioning runs, move the lever to SUMMER, which is closed. Makers say the damper should stay closed the whole cooling season, so cool air does not loop back through the furnace.
No lever? That is okay. Some humidifiers work differently, so just ask your owner how yours is set up.

Try it

Your furnace humidifier checklist

From the guide’s own checklist. Tick each one as you go. These are examples; your home may need others.

0 of 6

Humidifier and its humidistat found
Damper on WINTER for the heating season, SUMMER for cooling
Water pad changed this heating season (ask your owner)
No drips at the water line or fittings
Drain hose runs downhill into the drain, with no dips or kinks
Owner or heating pro number saved

If something goes wrong

Turn the humidistat to OFF.
If you know where the small water valve on the humidifier line is and it turns easily, turn it off. If not, leave it.
Wipe up any water so nobody slips.
Take a photo and message your owner right away.
A musty smell or spots near the humidifier are worth reporting too, since moisture in the wrong place can lead to mold.

Turning it off and sharing it early is exactly right. Small drips are much easier to fix than water damage.

An everyday example

In January, a home felt bone dry, with a static shock at every doorknob, even though the furnace had a humidifier. The damper had been left on SUMMER since July, and the pad was crusted solid. With the damper on WINTER and a fresh pad, the static was gone within two days.

Test yourself

How much do you remember?

4 quick questions from this guide, with a one line why for each. Totally optional, no sign in, and your answers are never saved.

From The Perfect Series

Go deeper with The Perfect Seasonal Home Care Checklist Workbook

Fall, spring and everything in between. Simple, step by step checklists you can write in, one topic at a time, to help any home stay warm, safe and dry all year.

See The Perfect Seasonal Home Care Checklist Workbook All books in The Perfect Series

Keep this guide handy

Save this page, come back to your checklist any time, and share it with anyone in your home who could use it.

See all guides

From the Bunklow shop

Take it with you

Bunklow Home Guide 011: Whole-House Central Furnace Humidifiers and Evaporative Pad MaintenanceA printable guide to whole-house central furnace humidifiers and evaporative pad maintenance, in plain steps.
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This guide shares general information to help you, and is not legal, tax or safety code advice. Rules vary by state and city, so check with your local officials or a qualified professional. Please follow the maker's instructions for your equipment. Bunklow does not inspect properties or make repairs.