Condensation on the inside of windows

Symptoms

• Water droplets or fog on the room-side of the glass
• Worse in the morning or during cooking/showering
• Sometimes drips onto the sill
• Occurs mainly in winter

Likely causes

• CommonHigh indoor humidityCooking, showers, and drying laundry indoors raise moisture that condenses on the coldest surface, the glass.
• CommonPoor air circulation near the windowClosed curtains or blinds trap moist air against cold glass.
• PossibleSingle-pane or older glassLess insulated glass runs colder, making condensation more likely at the same humidity.
• PossibleToo-tight home sealing without ventilationNewer, well-sealed homes can trap humidity without enough fresh air exchange.
• PossibleCold snap dropping outdoor temperature sharplyA sudden cold spell can cause condensation even in normally dry homes.

What to do

1. Wipe the sill and glass dry to prevent water damage to wood or paint.
2. Run bathroom and kitchen exhaust fans during and after showers or cooking, and use a lid on pots.
3. Crack a window or use a whole-house or room dehumidifier if indoor humidity regularly reads above 40–50%.
4. Open curtains and blinds during the day to let air circulate over the glass.
5. Move humidity sources like drying racks and large numbers of plants away from problem windows.
6. Check that bathroom and dryer vents actually exhaust outside rather than into an attic or crawlspace.
7. If condensation is severe and constant, consider adding storm windows or upgrading to double-pane glass to raise the interior glass temperature.

Tools and parts

• Hygrometer (humidity meter)
• Dehumidifier (optional)

When to call a pro

Call an HVAC contractor if humidity stays high despite ventilation, since it may point to a whole-house ventilation or moisture problem.

Safety