How-to · Air & Climate
What Humidity Should Your House Be? Ideal Indoor Humidity by Season
Short answer: Keep the relative humidity inside your home between 30 and 50 percent. The US EPA recommends staying below 60 percent, ideally in that 30 to 50 range. Measure it with a cheap digital hygrometer, use a dehumidifier or air conditioner when it is too high, a humidifier when it is too low, and in a cold winter stay near the low end so your windows do not run with condensation.
What “relative humidity” means
Relative humidity (RH) is how much water vapor the air holds compared with the most it could hold at that temperature, written as a percentage. Warm air can hold more water than cold air. That is why the same amount of moisture reads as a lower RH when a room warms up, and why water condenses on a cold window: the air touching the glass cools until it cannot hold its water any more.
The ideal range, and why
| Indoor RH | What happens |
|---|---|
| Below 30% | Dry skin and throat, static shocks, cracked wood, irritated sinuses |
| 30 to 50% | Comfortable for most people; slows mold and dust mites |
| 50 to 60% | Acceptable, but dust mites and mildew start to thrive at the top end |
| Above 60% | Mold, mildew, musty smells, condensation, sticky air |
Dust mites, one of the most common indoor allergy triggers, depend on humid air to survive, and mold needs damp surfaces. Keeping humidity at or below 50 percent works against both. Going far below 30 percent trades one set of problems for another.
How to measure it
Buy a digital hygrometer, which usually comes combined with a thermometer and costs little. Put it at about chest height in the room you care about, away from the kitchen, the bathroom door, windows and heaters, and give it an hour to settle. Readings from cheap meters can be a few points off, so watch the trend over days rather than chasing a single number. Check a few rooms: basements and bedrooms with the door shut often read very differently from the living room.
Many thermostats, air purifiers and humidifiers also show humidity, but their sensors sit next to a heat or moisture source, so a separate hygrometer is more trustworthy.
Humidity too high: how to bring it down
Signs: condensation on windows in mild weather, a musty smell, mildew spots on walls, ceilings or window frames, peeling paint, or a reading that stays above 60 percent.
- Ventilate the sources. Run the bathroom fan during showers and for 20 minutes after. Use the range hood when cooking. Make sure the clothes dryer vents outside.
- Run the air conditioner. AC removes moisture as it cools. In a humid summer it may be all you need for the main rooms.
- Use a dehumidifier in basements, crawl-space rooms and anywhere that stays damp. Set it to 45 or 50 percent and let it cycle. Our guide on what size dehumidifier you need explains how to size one for the room.
- Fix water problems. Leaky pipes, gutters that dump water against the foundation, and a yard that slopes toward the house all feed a damp basement. A dehumidifier treats the symptom; fixing the leak treats the cause.
- Dry laundry outside or in the dryer, not on racks indoors in a humid season.
Humidity too low: how to raise it
Signs: static shocks, dry skin and lips, a scratchy throat in the morning, gaps opening in wood floors, or a reading under 30 percent. It is most common in winter, when cold outdoor air with little moisture is heated indoors.
- Use a humidifier, especially in bedrooms. See cool mist vs warm mist to pick a type. Set it to about 40 percent, not higher.
- Clean it often. A dirty humidifier tank grows bacteria and mold and blows them into the room. Our guide on how to clean a humidifier covers the routine.
- Use distilled water in ultrasonic humidifiers to avoid fine white mineral dust.
- Small helps: houseplants, air-drying a load of laundry indoors, and leaving bath water to cool before draining all add moisture.
Winter: why “ideal” moves lower
When it is freezing outside, the inside surface of windows and outside walls gets cold. Air at 45 or 50 percent touching that glass condenses into water, which can soak window frames and grow mold. In cold weather, keep indoor humidity around 30 to 40 percent, and if you see condensation on your windows, turn the humidifier down until it stops. Older, single-pane windows need lower humidity than modern double-pane ones.
Summer: the usual problem is too much
In humid climates, outdoor air in summer can carry far more moisture than you want inside. Keep windows closed on muggy days when the AC is running, and run a dehumidifier in the basement even if the rest of the house feels fine; basements stay cool, which raises their relative humidity.
FAQ
What is a good humidity level for a house?
Between 30 and 50 percent relative humidity for most homes. The US EPA recommends keeping indoor humidity below 60 percent, ideally 30 to 50, to limit mold and dust mites.
What humidity is too high indoors?
Above 60 percent for long periods. Mold, mildew and dust mites grow faster, rooms feel sticky, and you may see condensation on windows or a musty smell.
What humidity is too low?
Below about 30 percent. Dry air can cause dry skin, cracked lips, itchy eyes, static shocks and irritated sinuses, and it can make wood floors and furniture shrink and crack.
Should humidity be lower in winter?
Yes, when it is very cold outside. Indoor air at 50 percent humidity will condense on cold windows, so in a cold climate aim for the lower end, around 30 to 40 percent, and lower it further if your windows fog or drip.