Why Do My Windows Sweat Inside During Cold Weather?

Condensation forms when warm, moist air touches a colder surface, like your window glass. In cold weather, the glass drops below the dew point of the indoor air, so the moisture in the air turns into liquid on the surface. The more humidity in your home, the more likely you will see sweating on your windows.

Everyday activities add moisture to the air. Cooking, showering, drying clothes indoors, and even breathing all release water vapor. If your home is tightly sealed to keep out the cold, that moisture has nowhere to go, so it collects on the coldest surfaces, which are usually the windows.

Lowering the humidity in your home is the most effective way to stop window sweating. Use a dehumidifier in damp areas like basements or laundry rooms. Make sure your bathroom and kitchen exhaust fans vent to the outside, not just into the attic.

Ventilate your home by cracking a window for a few minutes each day, especially after cooking or showering. This lets moist air escape and brings in drier outdoor air. If you have a humidifier, turn it down or off during cold spells, as it adds moisture to the air.

For older windows, upgrading to double-pane or low-emissivity glass can reduce condensation by keeping the inner glass warmer. Adding weatherstripping or caulking around window frames can also help by preventing cold air from leaking in and reducing the temperature difference on the glass.

Storm windows or insulating window film are other options that add a layer of air between the room and the glass. If your windows are beyond repair, replacing them may be the right long-term solution. A professional can help you decide based on the condition of your frames and the extent of any water damage.