The Ideal Indoor Humidity Level: 30 to 50%, and When to Go Lower
The ideal indoor humidity level is 30 to 50%, per EPA, and below 60% at most. What happens outside that range, why winter settings go lower, and how to measure it.
Affiliate disclosure: product links on this page go to Amazon, or to the maker's own store for brands that sell only direct. As an Amazon Associate we earn from qualifying purchases, at no extra cost to you; a link to a maker's store earns us nothing. No retailer or brand sees our picks before they are published or has any say in them. How we choose.
The ideal indoor humidity level is 30 to 50% relative humidity. EPA's mold guidance says to keep indoor humidity below 60%, ideally between 30 and 50%, and its humidifier guidance says not to humidify above 50%. MedlinePlus, from the National Library of Medicine, suggests setting a humidifier to about 40 to 50%, and the National Wood Flooring Association recommends 30 to 50% year-round to protect wood floors.
In very cold weather, aim for the low end of that range, because humid indoor air condenses on cold windows and walls. A hygrometer, or an air quality monitor that reads humidity, is the only way to know where you are. This guide explains what happens above and below the range and how to stay inside it.
The recommendations side by side
| Source | Recommendation |
|---|---|
| EPA, A Brief Guide to Mold, Moisture and Your Home | Below 60%, ideally 30 to 50% |
| EPA, Use and Care of Home Humidifiers | Do not humidify above 50% |
| MedlinePlus (National Library of Medicine) | Set a humidifier to about 40 to 50% |
| National Wood Flooring Association | 30 to 50% and 60 to 80°F year-round |
| Penn State Extension, citing ASHRAE | 30 to 60% |
The sources overlap at 30 to 50%. That is the range to aim for, with 60% as a hard ceiling.
What happens when it is too humid
EPA says the key to mold control is moisture control, and that condensation can be a sign of high humidity. Its humidifier guidance adds that excess moisture can encourage the growth of biological organisms in the home, including dust mites and molds. MedlinePlus warns that running a humidifier too long can leave surfaces constantly damp, leading to mold and mildew. Signs that humidity is too high include fogged or wet windows, musty smells, damp spots on walls and mold in corners and closets. See signs your home is too humid and the humidity level that prevents mold.
What happens when it is too dry
MedlinePlus says dry air can irritate and inflame the airways in the nose and throat, and that a humidifier helps with that. Penn State Extension notes that during the heating season indoor humidity can easily fall below 30%, and Iowa State University Extension says winter levels in many homes fall to about 10 to 20%. Dry air also shrinks wood: the NWFA says gaps that appear and close with the seasons are normal. Static shocks and dry skin are other common signs. See signs your home is too dry.
Why winter settings go lower
Cold outdoor air holds little moisture, and when it is heated indoors its relative humidity drops. At the same time, windows and exterior walls get cold, and moist indoor air condenses on them. AIRCARE's humidifier manual includes a chart that lowers the recommended indoor humidity as the outdoor temperature falls, and says to lower the set point until condensation stops forming.
| Outdoor temperature | Recommended indoor humidity |
|---|---|
| 30°F | 40 to 45% |
| 20°F | 35 to 40% |
| 10°F | 30 to 35% |
| 0°F | 25 to 30% |
| -10°F | 20 to 25% |
| -20°F | 15 to 20% |
The practical rule is simpler: if windows fog or frost on the inside, turn the humidity down until they stop.
How to measure humidity
- A hygrometer. EPA's mold guide suggests using a meter to check humidity. Inexpensive digital hygrometers are widely sold.
- An air quality monitor. Most include a humidity sensor; Awair, for example, states ±2% for the Element. See the best air quality monitors.
- A humidifier's built-in display. Useful, but AIRCARE's manual notes that external hygrometer readings and humidistat readings may differ, and that humidity varies even within one room. Check with a separate meter across the room.
Place the meter away from the humidifier, windows and the bathroom, at about breathing height.
How to stay in the range
If it is too dry
- Use a humidifier sized to the room, with a humidistat if possible. See the best humidifiers.
- Use distilled water in ultrasonic units, as EPA recommends, to avoid white dust.
- Clean it every third day, as EPA advises.
If it is too humid
- EPA advises air conditioners or dehumidifiers when needed, exhaust fans or open windows when cooking, showering and running the dishwasher, and venting clothes dryers outside.
- Fix leaks and dry water-damaged areas within 24 to 48 hours, as EPA advises.
- In a damp basement, a dehumidifier is usually the answer. See the best dehumidifiers.
Room by room
| Room | Usual problem | What to do |
|---|---|---|
| Bedrooms in winter | Too dry | A humidifier set to 30 to 50%, lower when windows fog |
| Bathrooms | Too humid after showers | Run the fan or open a window while showering (EPA) |
| Kitchens | Steam from cooking | Exhaust fan vented outside (EPA) |
| Basements | Too humid in summer | A dehumidifier; insulate cold pipes (EPA) |
| Rooms with wood floors | Seasonal gaps | 30 to 50% year-round (NWFA) |
Frequently asked questions
What is the ideal humidity for a house?
EPA recommends keeping indoor humidity below 60%, ideally between 30 and 50%. MedlinePlus suggests 40 to 50% when using a humidifier.
Is 60% humidity too high indoors?
It is EPA's upper limit. EPA advises staying below 60% and ideally between 30 and 50% to control mold, and not humidifying above 50%.
What humidity should I keep my house in winter?
The low end of 30 to 50%, and lower in very cold weather if windows fog. AIRCARE's manual suggests 35 to 40% at 20°F outside and 25 to 30% at 0°F.
What is the best humidity for sleeping?
The same 30 to 50% range EPA recommends for the whole home. MedlinePlus suggests 40 to 50% when using a humidifier in a bedroom.
How do I know my home's humidity level?
Use a hygrometer or an air quality monitor with a humidity sensor, placed away from the humidifier and windows. EPA's mold guide suggests using a meter to check.
Is 30% humidity too low?
It is the bottom of EPA's ideal range. Below that, dry air can irritate the nose and throat, according to MedlinePlus, and wood floors and furniture shrink.
Sources
- A Brief Guide to Mold, Moisture and Your Home, US Environmental Protection Agency
- Use and Care of Home Humidifiers, US Environmental Protection Agency
- Humidifiers and health, MedlinePlus, US National Library of Medicine
- Avoiding Winter Weather Woes, National Wood Flooring Association
- Humidity and Houseplants, Penn State Extension
- The air in our home is extremely dry in winter. Should I mist the houseplants?, Iowa State University Extension and Outreach
- Console Evaporative Humidifier Model MA1201: Use and Care Guide, AIRCARE (Essick Air)
- Awair Element: Air Quality Monitor For Your House, Awair
Related guides
Air Purifiers and Ozone: Which Ones Emit It and How to Check
Filter-only purifiers do not make ozone. Ozone generators are designed to, and some ionizers and other electronic purifiers make it as a byproduct. Here is how to tell which is which.
CADR Explained: What Clean Air Delivery Rate Measures and Why It Matters
CADR is the one standardized number for how fast an air purifier cleans a room. Here is how it is measured, how to use it, why smoke CADR is the one to compare, and its blind spots.
Do Air Purifiers Help With Viruses? What the EPA and CDC Say
A HEPA purifier sized for the room can reduce virus-carrying particles in the air. It cannot stop transmission on its own, and some technologies sold for germs carry risks of their own.