Ask Focus on Energy

There are a variety of options. Read on for more.

You did not indicate where the condensation is occurring. I’ll assume it is an issue with your windows; since they are probably the coldest surface in your home, they are most likely to have condensation forming on them.

Condensation is a result of water in vapor form changing to liquid. It forms when surface temperatures are at or below the dew point. To avoid condensation, maintain surface temperatures above the dew point. This is accomplished by raising the surface temperature, reducing the relative humidity (RH) inside your home, or a combination of those two strategies.

First, consider turning off your humidifier. It does not make any sense to add humidity if you are experiencing condensation. If you are unwilling to turn off the humidifier, consider lowering the setting. We typically recommend the interior RH to be 30 to 40 percent during the heating season unless outdoor temperatures are at or below 10°F. At that temperature (or below), you may find it necessary to reduce the interior RH below 30 percent.

Increasing the home’s interior air temperature will reduce the interior RH, thus lowering the dew point as warmer air has an increased capacity to hold moisture in vapor form. This will also increase surface temperatures. We recognize this strategy will result in increased fuel use, but the trade-off might very well be worth the additional expense.

Another common strategy is to manually operate an exhaust fan (quiet bath fan, etc.). As you expel humid air from your home, an equal amount of fresh, dry outdoor air is pulled into your home, lowering the RH. An inexpensive “system” consists of installing as a dehumidistat switch to automatically control an exhaust fan. This switch activates the fan based on the RH setting that you control. Typically, this switch is turned off in the summer.

Another, more elaborate system consists of installing a radon mitigation fan (connected to your sump system) to depressurize the space below your basement slab. This system would operate 24/7 all year. By depressurizing the space below the basement slab, you reduce the amount of moisture that enters your home from that area. Two added benefits of a system like this are radon mitigation and a reduction of the need to operate a dehumidifier.

Another possible strategy would be to install an air-to-air heat exchanger. These units, which can be connected to your existing furnace’s ductwork, expel excessive humidity, and draw in fresh air while capturing a percentage of the heat energy of the outgoing air. Besides controlling indoor humidity, indoor air quality can be greatly enhanced with the operation of these units.

The Home Performance with ENERGY STAR® Program can help you better understand and solve this problem. To learn more, contact a consultant in your area or call Focus on Energy at 800.762.7077.
 

Published Friday, November 20, 2009