Yardtally is reader-supported. Some links on this page are affiliate links. As an Amazon Associate, Yardtally earns from qualifying purchases. See our Affiliate Disclosure.
Indoor humidity in winter drops fast once the furnace starts running every day, and you can feel it. Every winter at our house in Indiana I get shocked by every doorknob, my skin dries out, my lips crack, and gaps open up between the boards in the wood floors and trim. We’ve never run a humidifier, so I wanted to find out what’s actually normal and what fixes it.
This guide covers the ideal indoor humidity in winter, why the air gets so dry, the signs your air is too dry, how to measure it, 6 easy ways to fix it, and what to do if your house swings the other way and gets too humid.
What’s In This Guide?
What Should Indoor Humidity Be in Winter?
Aim for about 30 to 40 percent relative humidity in winter. The EPA recommends keeping indoor humidity below 60 percent, and ideally between 30 and 50 percent, all year. In winter, the lower half of that range is the safer target. Source: U.S. EPA — A Brief Guide to Mold, Moisture, and Your Home
Why not higher? When it’s cold outside, your windows are the coldest surface in the house. Warm, humid indoor air hits that cold glass and turns to water. NDSU Extension recommends keeping winter humidity around 40 percent and notes that, at that level, double-pane windows can start to fog once it drops below zero outside. On the coldest days, let it drift down toward 30 percent. The University of Minnesota Extension considers anything from about 25 percent in winter up to 50 percent generally healthy, and warns that moisture problems can start above 50 percent. Source: NDSU Extension — Window Condensation Common Problem
Why the Air Gets So Dry in Winter
Cold air can’t hold much moisture. When that cold outdoor air leaks into the house and the furnace heats it up, it can suddenly hold a lot more water, but there’s no new water in it. So indoor humidity drops, sometimes into the teens or low 20s. The more cold air that leaks in around drafty windows and doors, the drier the house gets. That’s why sealing drafts shows up below as one of the fixes.
Signs Your Indoor Air Is Too Dry
If your indoor humidity in winter is too low, you’ll usually notice it before you measure it:
- Static shocks every time you touch a doorknob, light switch, or another person
- Dry, itchy skin and chapped or cracked lips
- Dry nose and throat, especially first thing in the morning
- Gaps opening up between wood floorboards, around trim, or in wood furniture as the wood shrinks
- Houseplants with brown, crispy leaf tips
I check every box on that list each winter. The gaps in the wood floors and trim are the easiest to spot, and they close back up on their own once the humidity comes back in spring.
How to Measure Indoor Humidity
Don’t guess. A small digital humidity monitor (also called a hygrometer) shows the indoor humidity in the room. The EPA notes these meters are inexpensive and sold at most hardware stores. Put one in the main living area, away from the kitchen, bathroom, and any humidifier, and check it at different times of day. Knowing your actual number tells you whether you need to add moisture, and keeps you from overdoing it. Source: U.S. EPA — A Brief Guide to Mold, Moisture, and Your Home
6 Ways to Fix Dry Air in Winter
1. Run a portable humidifier
The quickest fix is a portable humidifier in the rooms where you spend the most time, especially the bedroom. An evaporative humidifier is a good choice. It blows air through a wet wick filter, and according to the EPA, it releases fewer minerals and germs into the air than ultrasonic or “cool mist” models. Set it to stop around 40 percent, or use your humidity monitor to check, so you don’t overshoot. Source: U.S. EPA — Use and Care of Home Humidifiers
2. Keep the humidifier clean
A dirty humidifier can do more harm than dry air. The EPA recommends emptying the tank, wiping it dry, and refilling it every day, and cleaning portable humidifiers every third day. Use distilled or low-mineral water. Tap water leaves scale in the tank and can send a fine white dust into the air. Never let the area around the humidifier get damp. If it does, turn it down. Source: U.S. EPA — Use and Care of Home Humidifiers
3. Seal drafts around windows and doors
Every draft brings in cold, dry air that the furnace then heats into even drier air. Sealing drafts helps hold onto the moisture you already have and lowers your heating bill at the same time. Foam weatherstripping around doors and caulk around window trim fix most leaks in an afternoon. Our guide on how to seal windows and doors for winter walks through each one.
4. Add moisture the free way
A few everyday habits put moisture back into the air without buying anything:
- Leave the bathroom door open after a shower and let the steam spread through the house
- Hang laundry to dry inside instead of using the dryer
- Simmer a pot of water on the stove, or leave the lid off while cooking
- Let bath water cool before draining it
- Group houseplants together, since they release moisture as they’re watered
These won’t fix very dry air on their own, but together they can bump the humidity up a few points.
5. Consider a whole-house humidifier
If dry air is a problem in every room, every winter, a whole-house humidifier attached to the furnace adds moisture to all the air as it’s heated. It’s a bigger job that usually takes an HVAC pro to install, but it means no tanks to fill. It does need regular maintenance, including a new water panel each season. While you’re at the furnace, check the filter too. Our guide on how to choose a furnace filter explains what to buy.
6. Keep the thermostat a little lower
Warmer air holds more moisture, so the hotter you keep the house, the lower your indoor humidity reads. Turning the thermostat down a few degrees, especially at night, nudges the humidity up and saves on heating at the same time. A thermostat schedule is one of the 15 tasks on our winter home maintenance checklist.
Our thermostat savings calculator shows how much a lower setting could save on your heating bill.
When Indoor Humidity Is Too High
It’s possible to overdo it. Signs your indoor humidity is too high in winter include water or frost on the inside of windows, damp spots on walls or ceilings, a musty smell, and mold around window frames. NDSU Extension warns that going much above 40 percent in winter risks condensation and mold. Source: NDSU Extension — Window Condensation Common Problem
To bring it down:
- Turn the humidifier down or off until the windows stay clear
- Run bathroom and kitchen exhaust fans during and after showers and cooking, and make sure they vent outside, not into the attic
- Open a window just a crack for a few minutes to let warm, moist air out
- Open the curtains during the day so warm air reaches the glass
Source: University of Minnesota Extension — Controlling Moisture Problems in Your Home
If you’re already seeing mold, our guide on mold in your house covers what’s dangerous and what you can clean yourself. For damp spots you can’t explain, see how to check for water damage.
Frequently Asked Questions About Indoor Humidity in Winter
What should indoor humidity be in winter?
About 30 to 40 percent for most homes. The EPA recommends 30 to 50 percent year-round, but in winter it’s safer to stay in the lower half of that range so moisture doesn’t condense on cold windows.
Is 25 percent humidity too low in winter?
It’s on the low end. The University of Minnesota Extension considers about 25 percent acceptable in winter, but most people feel more comfortable closer to 30 to 40 percent. If you’re getting static shocks and dry skin, bringing it up a bit will help.
Is 50 percent humidity too high in winter?
Usually, yes. At 50 percent, you’re likely to see condensation on windows when it’s cold outside, and that moisture can lead to mold around the frames. Keep it closer to 40 percent or lower in winter.
Why are my windows wet on the inside in winter?
The indoor humidity is too high for how cold the glass is. Warm, moist air hits the cold window and turns to water. Turn down the humidifier, run exhaust fans, and let the humidity drift lower on very cold days.
Does a humidifier help with static shocks?
Yes. Static builds up much more easily in dry air. Bringing indoor humidity up to the 30 to 40 percent range usually cuts down on shocks noticeably.
Where should I put a humidifier?
In the room where you spend the most time, usually the bedroom, a few feet off the floor and away from walls, windows, and furniture so the area around it doesn’t get damp. Keep it clean and refill it with fresh water every day.