One of the most frequently asked questions by home owners is what do do about condensation on their windows. It's messy, damages the wood sills and turns them black (mold). “In the winter I even have ice in the corners of the window glass.”
What's the Cause?
Condensation is caused by warm moist air coming into contact with a cold surface (window) in the winter and/or cool air-conditioned air coming in contact with a hot surface (window) in the summer. There can be only two reasons for condensation in your home:
- Too much humidity, and/or
- Poorly insulated surfaces (windows)
What's the Solution?
Decreasing the humidity level in the home is the first step to take. Purchase a hydrometer at the local hardware or box store. You want to keep the humidity level at less than or equal to 40% when the outside temperature is between 20° - 40°. (see below)
Outside temp Inside humidity
20 – 40 ° ≤ 40%
10 – 20 ° ≤ 35%
0 – 10 ° ≤ 30%
-10 – 0 ° ≤ 25%
Note: Decrease inside humidity level as outside temperature decreases.
How Do I Decrease the Humidity Level?
- If you have a humidity control on your furnace, just turn the humidistat down.
- Increase air circulation around affected areas.
- Turn furnace fan from “auto” to “on”.
- Open drapes and window coverings to expose windows to air movement.
- Turn on ceiling fans if available.
- Check your air filter to make sure it is clean.
- Increase the time your bathroom exhaust vent is running after showers. Put this switch on a timer so you don't forget.
- Open a window in a moist area like a bathroom.
- In summer use a dehumidifier to maintain a humidity level of about 50%.
What About Better Insulating the Surfaces (windows)?
It is very important to address humidity levels and air movement first. Even brand new high efficient windows will condense moisture if humidity levels are too high. If you think about it, the new windows will actually keep that moist air from escaping better than the old drafty windows.
Once humidity levels are addressed, then proceed to improve the insulation of your windows and adjacent wall and ceiling areas. Not only are windows damaged from excess humidity, but also walls can stain and metal throughout the house rust. By properly installing windows with a minimum U-factor of .30 and SHGC of .30 you can drastically improve the condensation problem. Also, have an insulation contractor or power company perform an energy audit to identify (with an infrared camera) the suspected areas that are letting warm moist air escape. This escaping of moist air can condensate and damage walls and attic space.
By following these tips you can beat the condensation problem.