Symptoms
- Water droplets or fog on the inside of window glass
- Water pooling on the sill
- Worse on the coldest days or overnight
Likely causes
- CommonHigh indoor humidity relative to outdoor temperatureCooking, showers, and even breathing add moisture that condenses on the coldest surface in the room, usually the window.
- CommonSingle-pane or older, less insulated windowsWindows with less insulating capability run colder on the inside surface, condensing moisture more readily.
- PossiblePoor air circulation near the window, such as heavy curtainsTrapped, still air against the glass condenses more than air that's gently moving.
What to do
- Wipe down condensation regularly to prevent it from damaging the sill, frame, or nearby wall.
- Run kitchen and bathroom exhaust fans during and after cooking or showering to vent humidity outside.
- Use a hygrometer to check indoor humidity; aim for roughly 30–50% in winter.
- Run a dehumidifier if humidity runs high, especially in colder months.
- Open curtains or blinds slightly to let air circulate near the glass, especially overnight.
- Consider window insulation film or draft strips for older single-pane windows as a lower-cost improvement.
- Look into window replacement or upgraded weatherstripping if condensation is chronic and windows are old or damaged.
Tools and parts
- Hygrometer
- Cloth or squeegee
DehumidifierSearch: “home dehumidifier”
Window insulation filmSearch: “window insulation film kit”
When to call a pro
Call a window contractor if condensation is chronic and tied to old, poorly sealed, or single-pane windows.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.