What humidity should your home be in winter?

Key takeaways

• Mayo Clinic puts the ideal indoor humidity at 30% to 50%, and the EPA advises against humidifying a home above 50%.

• ENERGY STAR says homes in colder climates should sit at 30% to 40% during the heating season to prevent window condensation.

• Warm air can hold more water vapor than cold air, so outdoor air that's heated indoors ends up with a low relative humidity.

• One Minnesota energy nonprofit suggests keeping indoor humidity below 40% when it's 20°F to 40°F outside, and below 15% at -20°F or colder.

• A hygrometer measures a room's humidity, and Mayo Clinic suggests a humidifier with a built-in humidistat to keep it in range.

Why winter air gets so dry

Relative humidity, the number a humidity meter shows, compares the water vapor in the air with the most that air could hold at its current temperature. The National Weather Service explains that warm air can hold more water vapor than cold air, so the same air has a higher relative humidity when it's cool and a lower one when it's warm.

In winter, cold outdoor air carries little moisture to begin with, and once it leaks indoors and gets heated, its relative humidity drops. Mayo Clinic lists central heating, wood-burning stoves, space heaters, and fireplaces as things that lower air humidity, and it notes that humidity levels tend to be lower in winter than in summer.

The University of Kentucky's physics department makes the same point in plain terms: heating cold air doesn't add any water to it, so the air inside a house is likely to be very dry in winter.

What humidity your home should be in winter

The short answer is 30% to 50%. That's the range Mayo Clinic gives as ideal for a home, and the EPA's indoor moisture guidance sets the same 30% to 50% as the ideal, with 60% as the ceiling. The EPA's humidifier care guide adds that you shouldn't humidify past 50%.

Winter narrows the band in cold places. ENERGY STAR's guidance on indoor humidity says homes in colder climates should stay at 30% to 40% during the heating season to prevent window condensation.

How outdoor temperature changes the target

Condensation forms whenever a window surface is cool enough for moisture in the air to condense on it, which is why a Minnesota Department of Commerce guide to home moisture says some condensation can be expected in winter. The colder it is outside, the colder the glass, and the less indoor humidity it takes to fog it. A level that's fine on a 35°F day can be too high on a 5°F night.

The Minnesota Center for Energy and Environment, a nonprofit, publishes a winter guide that steps the target down as the temperature falls:

The same guide's advice when moisture keeps building up on windows or walls is to turn off the humidifier and lower its setpoint before starting it again. It also notes that better insulation and air sealing help, because warmer interior surfaces are less likely to collect condensation.

Window type shifts the numbers too. The same Department of Commerce guide, using Lawrence Berkeley National Laboratory data, gives the example of insulated glass with a low-e coating and argon gas, which may tolerate 61% humidity at the center of the glass at 0°F, while its edge may show condensation at only 26%. If the edges of your windows fog first, that's the reason.

How to read a hygrometer

A hygrometer measures the amount of moisture in the air, and Mayo Clinic calls it the best way to test the humidity in your home. The device looks like a thermometer, and the EPA notes that hygrometers are sold at local hardware stores.

One heating and cooling manufacturer's placement advice is to set a hygrometer at least 5 feet off the ground, out of direct sunlight, and in a room without big temperature swings. Keep it a few feet from the humidifier, where the mist won't throw off the reading. Then check it at the same time each day, since relative humidity rises as air cools and falls as it warms.

One meter can't tell you about the whole house. Bedrooms with the door shut, a kitchen after dinner, and a bathroom after a shower can each read differently from the hallway, so move the meter around for a few days before you set a target for a particular room.

Signs a room is too dry or too humid

You'll often feel dry air before you measure it. Mayo Clinic says low humidity can cause dry skin, bother the inside of the nose and the throat, and make the eyes feel itchy, and that dry indoor air can irritate the sinuses and cause bloody noses and cracked lips. The American Academy of Dermatology notes that dry skin can flake, itch, crack, and even bleed.

Static shocks are another clue. According to the University of Kentucky's physics department, a nearly invisible film of water on surfaces carries static charge away when the air is humid. In dry air that film doesn't form, so charge builds up until it jumps as a shock when you touch a doorknob.

Too much humidity shows up on surfaces. Mayo Clinic says high humidity can make a home feel stuffy and cause water vapor to condense into droplets on walls, floors, and other surfaces, and the EPA treats condensation as a sign of high humidity.

Humidity targets room by room

The same 30% to 50% range applies to every room, and the outdoor-temperature limits above apply to every room with an outside window. What changes from room to room is how you get there.

• Bedroom: The American Academy of Dermatology's advice for dry skin is to place a portable humidifier in your bedroom and run it while you sleep. Our guide to the best humidifiers for sleep and bedrooms covers quiet models suited to a nightstand.

• Nursery: Use the same range, with a cool mist unit. The American Academy of Pediatrics says cool mist humidifiers are generally considered safer for young children than warm mist ones or steam vaporizers because there's no risk of burns, and it advises placing the humidifier near your child but out of reach.

• Living room: In a large or open-plan room, you'll want a humidifier rated for its square footage. Check the coverage the maker publishes against your floor area, and keep the hygrometer on the far side of the room so it isn't reading the mist.

• Bathroom and kitchen: These rooms make their own moisture. The EPA suggests running the bathroom fan or opening a window while showering, and using exhaust fans when cooking or running the dishwasher.

• Basement: If the meter reads high down there, a dehumidifier is the tool, and Mayo Clinic names damp basements as a common place for one.

How a humidifier helps hold the range

A humidifier with a built-in humidistat does most of the work for you. Mayo Clinic describes a humidistat as a built-in hygrometer that keeps humidity within a healthy range, and the EPA notes that it can be adjusted to the moisture level you want. Set it to the bottom of the range on the coldest nights and nudge it up once it's milder.

Without a humidistat, a separate hygrometer does the same job by hand. Run the humidifier until the meter reaches your target, then turn it down or off. If water condenses on windows, walls, or pictures, the EPA's advice is to move the humidifier, lower its humidistat setting, or run it less, and to turn the output down if the area around it gets damp.

Mist type isn't tied to humidity level. Warm and cool mist units both add moisture, and our cool mist vs. warm mist comparison explains which suits which room.

The upkeep's a short routine. The EPA recommends emptying the tank, wiping the surfaces dry, and refilling a portable humidifier daily, cleaning it every third day, and using low-mineral water such as distilled. If you'd like the steps in order, our guide on how to clean a humidifier walks through each one.

What to do this week

1. Buy a hygrometer and check your main rooms at the same time each day for three or four days.

2. Look up tonight's low and find the matching row in the outdoor-temperature table above.

3. Set your humidifier's humidistat to that limit, or to 30% to 40% if it's simply cold where you live.

4. Put a portable humidifier in the bedroom first and run it overnight, as the American Academy of Dermatology suggests for dry skin.

5. Check the windows each morning. If there's fog or water on the glass, lower the setting by a few points.

6. Once nights stay above 40°F, the warm end of the Minnesota guide's table, it's fine to raise the target toward 50%.

Frequently asked questions

What humidity should my house be in winter?

Between 30% and 50%. In colder climates ENERGY STAR suggests 30% to 40% during the heating season, and lower still on very cold days.

Why are my windows wet in the morning?

Indoor humidity is too high for the outdoor temperature. The EPA's advice is to move the humidifier, lower its humidistat setting, or run it less.

Where should I put a hygrometer?

Out of direct sunlight and away from the humidifier. One heating and cooling manufacturer suggests at least 5 feet off the ground, in a room that doesn't swing much in temperature.

Does a humidifier help with dry skin in winter?

Yes. The American Academy of Dermatology suggests running a portable humidifier in the bedroom while you sleep to add moisture that dry skin needs.

What humidity is best for a baby's room?

The same 30% to 50% as the rest of the home. The American Academy of Pediatrics considers cool mist the safer choice and suggests placing it near the child but out of reach.