What It Means
Window condensation is the film or droplets of water that collect on the room side of window glass. It forms when warm, moist indoor air touches glass that's colder than the air. The U.S. Environmental Protection Agency lists condensation on windows, walls or pipes as a possible sign that indoor humidityIndoor humidity levelHow much moisture the air inside a home holds, given as relative humidity. EPA advises keeping it below 60%, ideally between 30% and 50%. See more is too high, and says to dry it and deal with the moisture source quickly.
Try It: Step Through EPA's Fix for Wet Windows
Five steps from EPA's mold and moisture guidance. Press Next as you finish each one.
1. Dry the glass and sill
Wipe the water off quickly so it doesn't sit.
2. Measure the humidity
A small meter tells you the room's relative humidity.
3. Compare with EPA's range
Below 60%, ideally 30% to 50%.
4. Cut the moisture sources
Vent the dryer and stove outside, and run the bath fan when showering.
5. Dry the air if it stays high
Use an air conditioner or a dehumidifier.
That's the method. Keep the reading below 60%.
How It Sounds at Home
- "The bedroom windows are dripping again this morning."
- "Crack the window when you shower, the glass is soaked."
- "There's black stuff growing on the window sill."
The Breakdown
What to do, following EPA
- Wipe the water off the glass and the sill as soon as you see it.
- Measure the room's relative humidity with a humidity meter.
- Compare the reading with EPA's advice: below 60%, and ideally 30% to 50%.
- Cut moisture at the source. Vent the clothes dryer, the stove and any kerosene heater to the outside where possible, and run the bathroom fan or open a window during showers.
- If the reading stays high, use an air conditioner or a dehumidifier.
Short version to try today. Wipe the windows, then run the bathroom fan through every shower this week and see whether the morning glass is drier.
Where it points
| What you see | What EPA's guidance suggests |
|---|---|
| Water on the inside of the glass | Indoor humidity may be too high |
| Water on walls or pipes as well | The same sign, so act quickly on the source |
| A reading of 60% or higher | Above EPA's limit, so cut moisture and dry the air |
Good to Know
EPA's moldMoldA fungus that grows indoors wherever moisture lingers. EPA says fix the water problem, then scrub it off hard surfaces with detergent and water. See more guidance starts from moisture: mold spores won't grow without it, so controlling moisture indoors is how mold gets prevented, and EPA asks for quick action when condensation shows up. For mold that's already there, see EPA's cleanup advice on the mold page before scrubbing.
FAQ
Why are my windows wet on the inside in the morning?
Warm, moist indoor air is meeting cold glass. EPA treats condensation like this as a sign that indoor humidity may be high.
How do I stop condensation on my windows?
Lower the indoor humidity. EPA suggests venting dryers and stoves outside, running the bathroom fan while showering, and using an air conditioner or dehumidifier to keep humidity below 60%.
Can window condensation cause mold?
It can. EPA's guidance is that mold needs moisture to grow, and it says to dry condensation quickly and reduce the moisture source.
Do It in Buhata
Tasks
Add "Wipe the window sills and check the humidity" to Tasks with a daily repeat for the cold months.
Open BuhataRelated Terms and Categories
- Indoor humidity level
How much moisture the air inside a home holds, given as relative humidity. EPA advises keeping it below 60%, ideally between 30% and 50%.
- Mold
A fungus that grows indoors wherever moisture lingers. EPA says fix the water problem, then scrub it off hard surfaces with detergent and water.
- Mildew
A flat, usually gray or white mold that grows on damp surfaces such as shower grout, curtains and fabric left wet.
- Window cleaning
Washing window glass, inside and out, so it's clear and streak-free; window makers suggest doing it at least twice a year.
- Attic ventilation
The flow of outside air through an attic, in at vents under the eaves and out near the peak, that carries moisture out and keeps the attic cold in winter.
- Dryer vent cleaning
Clearing built-up lint out of the duct that carries a clothes dryer's hot, damp air outdoors. NFPA advises cleaning the vent pipe at least once a year.
Sources
EPA, "A Brief Guide to Mold, Moisture and Your Home"; EPA, "Mold Course Chapter 2"; EPA, "Text Version of the Mold House Tour"
- www.epa.gov/mold/brief-guide-mold-moisture-and-your-home
- www.epa.gov/mold/mold-course-chapter-2
- www.epa.gov/mold/text-version-mold-house-tour
Last updated .