'Sweating windows': big winter problem

During winter months we receive loads of questions about what causes windows to "sweat" and what to do about the problem. Beyond being a nuisance, this condition can lead to mold, rot and a musty odor throughout a home. Making matters worse, for those in especially cold climates, the sweat freezes and turns to ice.
This excessive moisture that is commonly referred to as "sweating windows," is really condensation -- water vapor in the air turning into liquid water. It's the same condition that occurs when a cold can of soda is removed from a refrigerator and exposed to room temperature -- beads of moisture collect on the outside surface of the can to form a layer of condensation.
Many modern energy-efficient windows have features built in to keep the temperature of the glass as warm as possible and thus reduce condensation. For example, insulated glass provides superior energy efficiency to reduce the potential for condensation.
However, there is no such thing as a condensation-free window in high-humidity conditions. Controlling the amount of moisture in your home is the most effective action you can take to avoid condensation.
Replacement windows
Window replacement can do wonders to improve energy efficiency and increase home comfort, but it may do little to avert sweaty window syndrome. In fact, just the opposite may be true.
Ironically, many homeowners are discovering that their new energy-efficient windows have more condensation that their old ones.
Though well-insulated, tight-fitting windows provide draft-free comfort and can help lower your fuel bills, airtight windows can trap moisture inside your home. Previously, moisture in the air may have leaked to the outside through openings in your old loose-fitting windows, thus preventing condensation.
Drying out
Here are a few ways to dry out sweating windows:
U Open window blinds during the day. This allows sunlight in and will warm interior air to create natural air currents. The improved circulation results in more even temperature.
U Use fans in bathrooms, kitchens and laundry rooms to remove excess moisture in the air. Bathing, cooking and doing laundry are activities that contribute the most to raising indoor humidity and, consequently, sweating windows. If you don't have ventilation fans in each of these spaces, install them. If you do have them, use them.
And it isn't enough just to turn them on while you are performing the activity -- allow them to run for a period afterward to fully remove excess moisture.
The biggest mistake that most folks make is that they turn the bath fan off just as soon as they finish bathing. Instead, let the fan run for up to half an hour to fully remove excess moisture. The same holds true when cooking and doing laundry.
U Use a ceiling fan. Many people believe that a ceiling fan is useful only to cool you down on those sticky summer evenings. In reality, a good ceiling fan is like money in the bank year-round.
In winter, run the fan in the reverse direction at a low to moderate speed. The blades will push air upward toward the ceiling and down across walls and windows. This air movement will make for more even heating and will dry most windows of condensation.
U Air out your home frequently by opening doors and windows. Before there were mechanical vent fans, ceiling fans and dehumidifiers, opening doors and windows was the only means of improving ventilation and removing condensation. Despite technology, there is no replacement for a little free air and the benefits that it can have on improving indoor air quality.
U Reduce the number of indoor house plants, as plants increase humidity levels. If you have a terrarium, you know that the inside surface of the envelope is covered with condensation. That's no accident -- plants and damp soil increase humidity. If you have sweaty windows and lots of houseplants, you may need to thin out some of the plants indoors to clear the windows.
U Use a dehumidifier to remove excess humidity from the air. A dehumidifier is essentially an air conditioner that has both hot and cold coils in the same container. A fan draws humid air over the cold coil of the air conditioner to condense moisture, which then drips into a collection container. Dry air passes over the hot coil to restore it to its original temperature.
For best indoor comfort and health, a relative humidity of about 45 percent is ideal. You can track your home's humidity with an inexpensive hygrometer.
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