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How to Prevent Window Fogging and Condensation

Household condensation, or “sweating”, on windows is a result of humidity comes in contact with a cold surface such as a mirror or glass window, it turns to water droplets and is called condensation. This is perfectly normal and all homes will occasionally have some condensation on their windows.

Window World customers enjoying new windowsKeep in mind that excessive window condensation, frost, peeling paint, even moisture spots on ceilings and walls can be signs of excessive condensation and possibly damaging problems in your home. We tend to notice condensation on window and mirrors first because they are not porous and moisture cannot penetrate these surfaces. This is an indication that you may have a moisture problem that needs to be addressed.

NOTE: Windows do not cause condensation.

You may be wondering why you see more moisture now that you have replaced your old, drafty windows with energy efficient ones. It’s simple really, your old windows were drafty and allowed humidity to escape. Now that your new windows create a much tighter seal, the excess moisture us unable to escape and therefore collecting on your windows. Again, windows do not cause condensation, instead they prevent humidity from escaping and provide an easy surface for condensation to collect.

Where is the humidity coming from?

There are many common things that generate indoor humidity such as your heating/air unit, humidifier, showers, etc. Everything you do in your home that involves water, like mopping the floors, contributes to the problem.

The condensation you see on your windows is more likely to occur where the outside temperature is much lower than the inside temperature. The greater the difference the greater the opportunity for condensation.

Reducing humidity is the key to reducing condensation.

The best way to reduce condensation is to lower the humidity in your home. So, how much humidity is too much? The following table illustrates the recommended comfortable levels of indoor humidity during the winter months.

OUTSIDE TEMPERATURE INSIDE RELATIVE HUMIDITY
-20°F 15 to 20%
-10°F 15 to 20%
0°F 20 to 25%
+10°F 20 to 30%
+20°F 30 to 35%
(Indoor humidities can be measured with a humistat or psychrometer.)

Five easy steps to controlling indoor humidity.

  1. Make sure all sources of ventilation to the outside are working. If bathroom exhaust fans, attic vents and laundry room vents are not working excess moisture is building up.
  2. Air out your home periodically. Opening windows for just a few minutes a day lets excess moisture escape and the fresh dry air enter.
  3. Check your humidifier setting. Make sure you are following the instructions for your humidifier.
  4. You can even open your fireplace dampers to allow excess moisture to escape.
  5. Do your best to not over-water your house plants.

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