Problems with condensation on windows? Watch humidity levels

ST. PAUL, Minn. (3/5/2007) - A common condition found in Minnesota homes during the winter, excessive condensation on windows and other surfaces indicates that indoor humidity levels are too high.

The relative humidity inside your house should be just high enough so that people are comfortable. Excess humidity may cause problems -- on the windows, in the walls and in the attic. It also impacts wood floors, furniture and human health.

Relative humidity is a function of moisture in the air and temperature. Warm air holds more moisture. If a window is colder than the surrounding air, the moisture in that air condenses when it comes into contact with the cold surface. Some condensation can be expected in cold weather. The colder the outdoor temperature, the more likely you are to have condensation.

The best way to control condensation is to keep relative humidity low. Consider sources of moisture that make relative humidity high, such as the kitchen, bathroom and laundry room:

• You can control moisture by providing adequate ventilation directly outside from these rooms. Use bathroom fans during and after showers and baths.
• Install a timer that keeps the fan running for at least 15 or 20 minutes after showering or bathing. This removes most of the excess moisture.
• Use kitchen fans that vent directly outside during and after cooking or baking. They remove moisture and reduce relative humidity inside.
• Make sure clothes dryers are properly vented. You don't want moisture being removed from clothes to get in the house.
• Make sure vent ducts for the dryer are sealed and as short as possible. Sealing them assures that excess moisture leaves the house and doesn't end up in the floor or wall, where hidden mold and damage happen.

In preparation for next winter, make sure your windows are sealed. Caulk where the inside frame meets the wall, and between the frame and the sash. Use weather stripping to close gaps on sliding window parts.

If condensation problems persist, consider a whole-house ventilation system. These balanced systems manage humidity and keep indoor air healthier. This means fresh air is brought into the house in the same amount that is being exhausted. Many systems recover the heat from the outgoing air in the winter to save energy.

Media Contact: Julie Christensen, U of M Extension, (612) 626-4077, reuve007@umn.edu

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URL: http:// www.extension.umn.edu/extensionnews/2005/humiditylevelsl07.html  This page was updated Mar. 5, 2007 .
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