What Causes Window Condensation

Condensation on Window

If you are wondering what causes window condensation, then this post gives you the key reasons why this may be happening.  Like the canary in the coal mine, in some cases it can be a pointer to serious conditions that may be affecting your home. If you are still left with questions after reading this article, then an Arcana Windows and Doors consultant will be happy to discuss with you your concerns.

Window condensation is a problem that often occurs in Canadian homes, given the extreme cold temperatures that are encountered in winter. In some cases, the quality of the windows is the root cause. However more often there are other reasons for this problem and the condensation actually proves good insulation of the windows.

Types of Window Condensation

There are three places where condensation may be seen on windows.  

  • Exterior window condensation is simply frozen dew and occurs when the window is colder than the dew point.
  • Condensation between window panes occurs either when the seal between the panes is broken or when the desiccant inside the windows has become saturated.
  • Interior condensation, or the condensation that occurs on the inside of your windows, is the most common type, and there are a variety of reasons for this and ways you can remedy the problem.

Interior Window Condensation

Interior condensation on windows is linked to the following factors:

  • Exterior temperature
  • Interior temperature
  • Interior relative humidity

The homeowner has control only of the last two of these, and controlling the relative humidity is the most effective way of handling any problem. Most reliable sources of information suggests that a relative humidity between 30% and 50% in the winter is ideal. The lower the temperature outside, the lower the relative humidity should be. A hydrometer can be used to monitor the relative humidity. They are inexpensive and are easy to find in stores.

Changes in lifestyle to combat window condensation

The easiest way to combat window condensation is to change what may be long-term habits.

By such means you can  reduce the amount of water vapour you release into the air.  This will reduce the relative humidity.

  • Make sure you have good air evacuation for cooking and showers; make sure you keep the bathroom vent run at least 20 minutes after the shower end
  • Take shorter showers in the winter
  • Don’t close the blinds or curtains unless you need to thus allowing proper air circulation over the window
  • Keep interior doors open as much as possible thus ensuring good air circulation
  • Avoid large variations in room temperature
  • Keep fewer plants in the home
  • Avoid storing wood in the basement

Modify your home to reduce window condensation

You can reduce the relative humidity of a building by ensuring that its mechanical functions are optimized. Here are some simple examples of ways by which you can control the interior environment of your home.

  • Install heat sources directly below windows
  • Ensure good air circulation near windows and in closed rooms by using a ceiling fan or regular stand fan
  • Install a dehumidifier to control relative humidity
  • Install an air exchanger to improve ventilation and bring in fresh air
  • Make sure the dryer vent is properly installed and leak-proof so that humidity is directed outside the home


Window condensation is a seasonal problem that may happen when the weather gets very cold. You can easily control it through the adoption of certain habits and by simple changes to your home appliances.

If you find that despite such changes you are still having problems with window condensation, why not contact one of the Arcana Windows and Doors consultants who can advise you.

For a more extensive list of ways of handling problems, this article on How to stop condensation on windows is well worth a read.

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