Why Are the Windows in My House Wet & Fogged Up Inside?

Condensation

• Every home has moisture in the air, put there by everyday life, including cooking, bathing, washing dishes and even breathing. When you heat the air in your home in the winter, extra moisture will cling to cool surfaces, including windows, causing them to fog, similar to the sweating effect on the outside of a glass of cold water. When the wet air has nowhere to escape a sealed home, it continues to cause window condensation problems in the winter unless you control the humidity level properly.

Controlling Humidity

• Once the relative humidity in a home in the winter rises much beyond 40 percent, water likely will begin condensing on windows. Buy an inexpensive meter at a hardware or home improvement store to keep an eye on the humidity level to keep condensation in check. Proper home venting allows air exchange, which helps keep the relative humidity level between 30 percent and 40 percent. Bathroom fans and range hood fans also help remove excess moisture from the home. You can try a dehumidifier if the level gets too high, but they generally work much better during humid summer weather.

Side Effects

• A little moisture seen occasionally on a window in a bathroom or kitchen presents little more than a nuisance and goes away if you control the moisture from cooking or bathing. More extensive moisture on windows damages paint, wood and walls over time, even causing mold inside the window frames, attic or walls. You especially have a moisture problem if you see heavy moisture on windows in areas of the home away from the kitchen or bathroom. If you have such a problem, check your walls, closets and floorboards behind furniture for signs of moisture.

Other Remedies

• Increase the insulation value of your windows, such as going from single-pane to double-pane, or adding a plastic cover in the winter, can raise the temperature of the glass enough to cut down on condensation. Once you see moisture collecting on double-pane or triple-pane windows, you know your humidity level has risen too high. Modern builders often create airtight homes that may require an air-to-air-exchanger to keep fresh air circulating in the home and reduce moisture.