How to track indoor humidity
For ideal indoor humidity, set one digital humidity meter in your basement and another in a room you use every day, then check them regularly. EPA says to stay below 60%, ideally 30 to 50%. In cold weather, aim lower as the temperature drops outside. If the basement stays high, a dehumidifier set around 55% is the usual fix.
What ideal indoor humidity means, and why winter is different
A humidity meter, or hygrometer, shows the moisture in your air as a percentage. One reading tells you little. You're looking for a pattern across rooms and seasons, so place meters where the air is typical, away from showers, kitchens and exterior doors.
Two numbers guide you for most of the year. EPA says to keep indoor humidity below 60%, ideally 30 to 50%, because mold grows on damp materials. Above that, you can get condensation, mold and water damage to building materials.
Winter is different, and this is where a fixed target goes wrong. Cold outdoor air chills your windows and exterior walls, so humid indoor air condenses on them. The colder it gets outside, the drier your home needs to be. The Minnesota nonprofit Center for Energy and Environment (CEE) publishes limits for cold climates. A target of 30 to 40% suits milder winter days, but it's too high on a very cold night.
How to track indoor humidity with two meters
- Buy two meters
A basic humidity meter costs about $10 to $50, and many also show temperature.
- Place them well
Keep both away from bathrooms, cooking and outside doors, so they show typical air.
- Let them settle
Give them a day, then note the readings as your starting point.
- Check on a schedule
Look weekly at first, and also after big weather changes. Some meters store the day's high and low.
- Adjust for the weather
In a cold snap, compare your reading with the chart and turn down any humidifier.
- Add a dehumidifier if needed
Do this if the basement stays near or above 60% after you've dealt with leaks and drainage.
- Look for condensation
Check windows and cold pipes on cold mornings. Wipe the water away and lower the moisture source.
Ideal indoor humidity by season and outdoor temperature
| Season or outdoor temperature | Keep indoor humidity | Source |
|---|---|---|
| Any time of year | Below 60%, ideally 30 to 50% | EPA |
| Winter, 20 to 40°F outside | Below 40% | CEE |
| Winter, 10 to 20°F | Below 35% | CEE |
| Winter, 0 to 10°F | Below 30% | CEE |
| Winter, -10 to 0°F | Below 25% | CEE |
| Winter, -20 to -10°F | Below 20% | CEE |
| Winter, -20°F or colder | Below 15% | CEE |
Your house changes these numbers. Leaky homes run drier, and windows, insulation and air sealing all shift the point where condensation starts. If you see water on the glass, you're too high for today's weather, whatever the chart says.
| Sign | Likely cause |
|---|---|
| Condensation on windows or exterior walls | Too humid for the outdoor temperature |
| Damp feel, musty smell, mold spots | Too humid, or a hidden leak |
| Dry skin, shrinking wood doors and furniture | Too dry, which can point to air leakage |
What to do if indoor humidity is too high or too low
When humidity runs high, find the source first. EPA points to leaks, poor grading and gutters, along with cooking, showers and unvented dryers. Fix those and you may not need a machine.
For a basement that stays damp, CEE suggests a dehumidifier at 55%, or lower if it still feels damp. It recommends an ENERGY STAR model with an energy factor of at least 2.0. Empty the bucket regularly, or connect the unit to a drain.
In summer, air conditioning is the most effective way to dry a house, CEE says. An old, undersized or struggling system may not remove enough moisture, even when the temperature feels fine. If rooms feel clammy with the AC running, ask an HVAC technician to check it.
If your home is too dry in winter, a small humidifier run in short bursts works better than a set-and-forget whole-house unit, according to CEE's auditors. Turn it off if condensation appears. If you see mold covering more than about 10 square feet, follow EPA's advice and consult a professional.
What homeowners say about a good humidity level for a house
Test each bathroom fan after a hot shower. If it's loud or can't clear the steam within about 30 minutes, one owner says to replace it. (Reddit)
Basement dehumidifier setting and other humidity questions
What is a good humidity level for a house?
EPA says below 60%, ideally 30 to 50%. In cold winters, you may need to go lower to keep condensation off your windows.
What should I set my basement dehumidifier to?
CEE suggests 55%, or lower if the space still feels damp. Use your own meter to confirm the room is reaching that level.
Why are my windows wet in winter?
Indoor air is too humid for how cold the glass is. Reduce moisture sources, use your bath and kitchen fans, and compare your reading to the winter chart.
General guidance for U.S. homes, not professional advice. For gas, electrical and structural work, call a licensed pro.