Condensation: What Every Homeowner Needs to Know

The Facts about Condensation

Contrary to what you may have heard, there are no windows that “prevent” condensation.  Common household condensation, or “sweating” on windows, is in fact caused by excess humidity or water vapor in the home.  When water vapors in the air comes in contact with a cold surface such as window glass, it turns into water droplets and is called condensation.  All homes have occasional condensation, such as a little fogging on the windows especially prevalent in wet rooms such as bathrooms and kitchens, and this is no cause for concern.

In fact, you may notice that your energy-efficient replacement windows show more condensation than your old windows.  This is because your old, drafty windows allowed moisture to escape, while your new windows create a tighter seal which prevents the moisture (and your heating and cooling) from escaping the home, thereby allowing excessive humidity to build more condensation on the windows.

However, excessive window condensation, frost, peeling paint, or moisture spots on ceilings and walls may be signs of excessive condensation and moisture and the potential for damage to your home.  This is a sign that you probably need to reduce the amount of indoor humidity of your home.

What Causes Indoor Humidity?

All air conditioners contain a certain amount of moisture. There are many other common things that generate indoor humidity as well, such as your heating system, humidifiers, cooking, and showers. In fact, every activity that involves water, even mopping the floors, contributes to moisture in the air.

Condensation is more likely to occur in homes where January temperatures drop below 35 degrees Fahrenheit because there are greater extremes affecting the glass in the home.

It is very normal to experience condensation at the start of each heating season. During the humid summer months your home absorbs moisture and then perspires when you turn on the heat. This is only temporary, as after the first few weeks of heating your home should dry out.

Home remodeling and building projects may also contribute to indoor humidity due to high levels of moisture in wood, plaster, and other building materials, and your home will temporarily sweat during the first few weeks of the heating season.

Another factor in condensation is progress. With today’s modern insulation, moisture-barrier materials, and air-tight construction, we all enjoy a more thermally efficient home that blocks the cold out yet traps moisture in.

Window Moisture

Six Simple Steps to Controlling Indoor Humidity:

1Make sure all sources of ventilation to the outside are functional and use kitchen, bathroom, and laundry room exhaust fans during and after hunidity-producing activities to vent excess moisture.
2Air out your home periodically. Opening the windows for just a few minutes a day lets the stale moist air escape and the fresh dry air to enter without compromising your heating.
3Check your humidifier settings. Use the humidity comfort levels provided in the table below to correctly set and balance the humidity level in your home.
4Be sure that all louvers in the attic or basement are open and large enough. You can even open up your fireplace dampers to allow excess moisture to escape.
5If you have a large amount of house plants, try to concentrate them in one area and be careful not to over water.
6If troublesome condensation persists, see your heating contractor about an outside air intake for your furnace, venting of gas burning heaters and appliances, or installation of venting fans.

Recommended Temperatures
Outside Temperature Recommended Relative Humidity
+20 degrees F and above 35% to 40%
+10 degrees F 30%
0 degrees F 25%
-10 degrees F 20%
-20 degrees F 15%

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