Why Do My Windows Sweat in the Summer?

Though homeowners may believe that sweating windows are a sign of old or bad windows, the windows themselves have nothing to do with the formation of condensation. Windows show the first signs of condensation in both summer and winter due to the fact that the glass gets colder first in winter and remains cooler in summer than other materials in your home.

Summer is a humid time in many areas of the United States. Indoor cooling systems, on the other hand, such as central air or window-unit air conditioners, put out a dry air that reduces the humidity inside your home. Since the air outside is hotter and more humid than the air on the inside of the window, and since the glass is cooler than the outside air due to interior cooling, the humidity from outside forms on the window as condensation.

Condensation usually appears early in a summer season when the air conditioning unit is first turned on and gradually dissipates after a few days. If the condensation stays around for several weeks, it has the potential to cause damage to areas of the window that are prone to mold, mildew and rot, such as the wood frame. Since summer condensation usually forms on the outside of a window instead of the inside of the window, like winter condensation, however, it poses less of a threat.

Though the exterior sweating of windows during the summer doesn't carry a high risk to your windows or your home, you can still take some steps to eliminate it. The key is to bring the level of humidity in your home closer to the humidity outside. This can be accomplished by running a humidifier in the areas of your home where windows are sweating, or by putting potted plants, which release moisture into the air, by the windows. Avoid adding too much humidity to your home, though, because excess indoor humidity can cause the growth of mold and mildew.