Extension and Ag Research News


Window Condensation a Relatively Common Problem

The NDSU Extension Service’s energy educator offers tips on reducing condensation in windows.

Another cold snap is on the way. That means you soon may be dealing with condensation on your windows.

“A thin film of moisture is nothing more than a nuisance, but as the air continues to cool, more moisture forms on the window, which eventually can lead to damage to the window and surrounding wall as ice forms,” says Carl Pedersen, North Dakota State University Extension Service energy educator. “Excess moisture also can be a breeding ground for mold.”

Condensation can occur even though you made sure to seal your house properly last fall by running a fresh bead of caulk around the windows and replacing the worn-out weather stripping around the front door.

Air has an ability to hold different amounts of water vapor, depending on the temperature, according to Pedersen. The warmer the air, the more room for water. Colder air has less room for water molecules, so they start to stick together. When the heated air in your house comes in contact with the cold air next to your windows, it cools. The cooler air causes the excess moisture to form condensation.

“The same thing happens on a glass of your favorite chilled beverage,” Pedersen says.

This excess moisture comes from a variety of sources. Each person in a house adds 3 pints of water vapor to the air every day just from breathing. Add to this the water from showers, cooking and laundry and it adds up quickly.

To control condensation, you first need to look at where it is occurring on your windows, Pedersen advises. If it is between the inside and storm window, you most likely have air leaking out of the house. This warm air carries moisture with it. A temporary fix would be to cover the window with plastic film. Another possibility is to use temporary weather stripping around the window tracks. It can solve the problem of air leaks and be removed in the spring.

If you are noticing condensation on double- or triple-pane windows, you most likely have too much humidity in your house. You should strive for relative humidity levels around 40 percent in the winter. Any higher and you risk condensation and mold issues; any lower and the air is too dry. Air that is too dry can cause dry skin and nasal passages, which could lead to respiratory illness.

With a double-pane window, condensation should begin to appear when the outside temperature dips below zero if the relative humidity level in the house is 40 percent. With triple-glaze windows, condensation should not begin to show until the outside temperatures reach closer to minus 40 F.

If humidity levels are considerably higher than 40 percent, you can begin running vent fans in the bathroom and kitchen to reduce these levels. Just make sure they vent to the outside. Venting into the attic could cause unseen moisture problems, including mold growth, Pedersen says.

Many people use dehumidifiers, but they generally are ineffective if humidity levels are below 50 percent, which is common in the winter. If condensation is occurring on windows behind draperies, try leaving the drapes open at night.

“Unfortunately this causes energy losses, which need to be balanced with the decrease in window condensation,” Pedersen says.

Newer construction has created homes that are extremely airtight. The owners of these homes may want to invest in an air-to air exchange system, which brings dry air in from the outside and replaces the warm, moist air in your home. These systems use a heat exchanger to salvage as much as 70 percent of the heat from the indoor air.

A much simpler fix is to open a window for a little while. Crack the window an inch or 2 to lower the humidity levels in the house. Just make sure the window does not freeze open, Pedersen says.

If you have any questions on this or any other energy-related topic, contact Pedersen at (701) 231-5833 or carl.pedersen@ndsu.edu.

NDSU Agriculture Communication

Source:Carl Pedersen, (701) 231-5833, carl.pedersen@ndsu.edu
Editor:Ellen Crawford, (701) 231-5391, ellen.crawford@ndsu.edu
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