Short answer: keep indoor relative humidity between 30% and 50%. That's the range the U.S. EPA recommends, and it's where homes stay comfortable without the dampness that mold needs to grow. Above 60% for days at a time, problems start.
The Humidity Zone
- Below 30% — Dry. Dry skin and static, but no mold risk.
- 30–50% — Healthy. The target. Nothing to do but keep measuring.
- 50–60% — Watch. Ventilate and watch the trend. A day here is fine; a week isn't.
- Above 60% — Act now. Run a dehumidifier and find where the moisture is coming from.
Why you can't guess
Humidity doesn't feel the way you'd expect. A room at 72°F and 62% can feel fine, especially with the AC running. Your thermostat's humidity number, if it has one, measures only the hallway it hangs in. Closets, bathrooms and basements are almost always damper than the rest of the house.
How to measure it
- Put a hygrometer or Wi-Fi humidity sensor in the room you're worried about, away from vents and windows.
- Give it an hour to settle, then check it at the same time each day for a week.
- Watch the trend, not one reading. A bathroom hits 80% after a shower and should drop below 60% within an hour.
A Wi-Fi sensor keeps the history for you and sends an alert when a room crosses the line you set. Set the alert at 50%.
Room by room
- Bathrooms: run the exhaust fan during the shower and 20 minutes after. If the reading stays high, the fan may be too weak or vented into the attic.
- Closets: no airflow and wet shoes make them the dampest rooms in many homes. Leave the door cracked and dry shoes before they go in.
- Basements and slab-level rooms: cool surfaces and ground moisture push readings up. This is where a dehumidifier earns its keep.
- Laundry rooms: check that the dryer vents outside and that the washer hoses aren't seeping.
An Austin note
Central Texas summers are humid, and your AC is supposed to pull moisture out of the air as it cools. An oversized or short-cycling system cools the house fast and shuts off before it does that job, which leaves rooms cold and clammy. If your house feels that way, measure before you blame the AC, then have the system checked.
What to do when a room is out of range
- Find the source first: a leak, a missing vent fan, water pooling at the foundation.
- Improve airflow: open doors, run fans, keep furniture a few inches off exterior walls.
- Run a dehumidifier set to 45–50% with a drain hose so it never stops on a full tank.
- Keep measuring so you know it worked.
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Moisture Logic products help you find and control moisture. They don't remove mold that's already growing. If you see mold over a large area, talk to a remediation professional.