Got Condensation? Here’s Why and What to Do

We all recognize condensation when it forms on a glass of cold iced tea in August. But what does it mean when it forms on the inside of our windows? The same principal is at work on our windows and the iced tea glass: the cold surface meeting the warm, damp air causes moisture to form on the glass.

What is condensation and what can you do about it?

We usually see condensation forming on the inside of windows in the winter, especially at the beginning of the heating season. The cold air outside makes the window cold, and if the warm air inside has too much moisture, it will form condensation. In North Carolina, where the temperature usually rises well above freezing during the day, the condensation will usually dissipate during the day; however, that doesn’t mean that you should just ignore it.

Condensation on the inside of your windows indicates that your indoor humidity might be too high, which can cause much worse problems than foggy windows. Excessive humidity can cause paint to blister, wood to rot, floors to buckle, and insulation to deteriorate. Ironically, it’s often the newest, most energy efficient houses that can be prone to excessive indoor humidity; these houses are “tighter” and don’t allow air to flow freely through the walls to the outside. This keeps heating or cooling inside where you want it, but it also keeps humidity inside. Older houses were often built with more porous materials that allowed water vapors to escape.

Most experts agree on the following scale for indoor relative humidity, based on a range of outdoor temperatures:

  • -30° F or below – not over 15%
  • -20° F to -10° F – not over 20%
  • -10° F to 0° F – not over 25%
  • 0° F to 10° F – not over 30%
  • 10° F to 20° F – not over 35%
  • 20° F to 40° F – not over 40%

(Assumes 70° F indoor air temperature)

Since North Carolina winters are fairly mild, the humidity in your house should be in the 30 to 40 percent range for most of the season.

If your indoor humidity is too high, there are several steps you can take to bring those levels down:

  • Invest in a dehumidifier. They come in different sizes for different-sized spaces and can drastically reduce humidity. You can also buy moisture-eliminating products for high-moisture rooms like bathrooms or basements.
  • Add some air. Open windows for a little while each day, or run ventilation fans if you have them. If you don’t, consider investing in a ventilation system, which will keep your whole house dry.
  • Add some heat. Turning up the temperature will bring warm, dry air into the house, helping to reduce overall moisture.

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