Excessive condensation of moisture is an increasing concern in homes. The homeowner frequently assumes that window condensation is a fault of the window construction, when in fact their own living habits can greatly affect the humidity levels in their home. Condensation usually occurs first on windows because they have the lowest temperature of any of the interior surfaces in the house. Drapes or other window coverings can contribute to the problem by restricting the flow of warm room air over the glass surface.

Where Does Humidity Come From

  • Normal breathing and perspiration by a family of four adds a half pint of water to the air each hour.
  • Cooking can add up to four or five pints of water per day.
  • A shower can add another half pint.
  • Dishwashers, washing machines, and dryers can add several pints of water to the air.
  • Humidifiers which are adding too much humidity.
  • Any containers in the home that have water standing often or all the time such as sinks and pet bowls and open fish tanks.
  • Excessive plant containers that require watering.
  • Poorly insulated crawl spaces which allow humidity to invade the home.


Today, because we are all energy conscious, houses and windows are far more energy efficient. This makes us more comfortable, but may trap humid air inside the home. Your new BEST WINDOW and DOOR windows are designed to prevent air infiltration into and out of your home. Your old, drafty windows could allow the moisture in your home to escape while your new windows are tight and do not allow the moisture in your home to escape. You need to control the humidity in your home. If your indoor humidity is too high you notice condensation first on your windows, it could mean that your excessive indoor humidity is causing damage elsewhere in places you can’t see, such as: your walls, ceilings, floors, and your attic roof. Excessive indoor humidity can cause blistering and peeling paint, warping and rotting wood, as well as the formation of mildew. The source and amount of humidity in the air needs to be determined. Your first step is to find what the humidity level in your home is. You should monitor this regularly as the temperature outside varies. Devices that measure humidity are called hygrometers. They can be purchased at most reliable hardware and home center stores.

How Much Humidity Is Too Much and How Much Can Air Hold?
Warmer air holds more moisture than cool or cold air. This is illustrated on a humid, hot summer day when condensation appeared on a cold glass. This means that the amount of moisture in the air has reached its maximum and can’t hold any more. Therefore, it gets rid of it by condensing it on the nearest cool or cold surface. As air cools, it can’t hold as much moisture and therefore, condensation will appear more quickly. So what is the ideal amount of relative humidity in the air? Based on keeping an indoor temperature of 70° F, it will vary with the outdoor temperature. But as a guide, the following relationship should help.

Outside air temperature Inside relative humidity for 70-deg. F Indoor air temperature
-30º F or below not over 15%
-20º F to -10º F not over 20%
-10º F to 0º F not over 25%
0º F to 10º F not over 30%
10º F to 20º F not over 35%
20º F to 40º F not over 40%