Condensation on Windows: Will a Dehumidifier Help?
Often, yes, but only up to a point. Water collects on a window when the glass is colder than the dew point of the room air: warm, moist air touches cold glass, cools, and can't hold all of its water any more. Lowering the humidity lowers the dew point, so less water forms. The colder the glass, the drier the room has to be to keep it clear, which is why the same house can be fine in October and drip every morning in January.
Condensation is a humidity reading you can see
The EPA treats condensation on windows, walls or pipes as a sign of high humidity, and its advice is to act quickly: dry the wet surface and reduce the moisture source. Water that sits on frames and sills every morning is moisture that mold can use.
What to do about window condensation
- Measure. Put a hygrometer in the room for a few days. The EPA's target is below 60 percent, ideally 30 to 50.
- Cut the moisture you add. The EPA's list: run the bathroom fan or open a window when showering, use exhaust fans when cooking and running the dishwasher, and vent the clothes dryer to the outside.
- Dry what gets wet. Wipe sills and frames in the morning; materials dried within 24 to 48 hours usually don't grow mold, according to the EPA.
- Lower the humidity if it stays high. That's where a dehumidifier comes in. Size it with ENERGY STAR's chart and keep the room's doors and windows closed while it runs.
When a dehumidifier won't clear the glass
- Very cold single panes. On the coldest mornings, glass can be cold enough to collect water even at a reasonable humidity. The window is the limit then, not the dehumidifier.
- A cold room. ENERGY STAR notes that frost can form on a dehumidifier's coils when the air drops below 65°F, which cuts its output. An unheated room in winter is a hard place for a standard unit.
- Condensation between the panes of a double-glazed window is inside the sealed unit. Room humidity doesn't reach it, so a dehumidifier can't change it.
- One room in a damp house. If every window in the house sweats, the moisture source is house-wide, and a single portable unit in one room won't keep up.
Not sure whether you need a dehumidifier or something else? Dehumidifier or moisture absorber covers small spaces, and air purifier vs dehumidifier covers the other common mix-up. If it's not just the windows, why a house gets too humid goes through the causes.
Where this comes from
U.S. EPA, A Brief Guide to Mold, Moisture, and Your Home (updated February 18, 2026). ENERGY STAR, Dehumidifiers. Both read October 5, 2026. The explanation of dew point and cold glass is general physics.