Condensation on windows occurs when the surface temperature of the glass on the inside of your home is lower than that of the humid air around it. The moisture vapour in the air changes into liquid water on contact with these cold surfaces. The more humidity in your home, the more likely you will experience condensation on your windows.
During the winter months most homes are heated between 20-22 degrees Celsius. When the temperature outside gets colder, the glass surface also gets colder, lowering the dew point (the temperature where humidity turns into liquid water or condensation). A humidity level of approx 30% is recommended, although this number can change depending on how cold it is outside.
The best way to avoid condensation on your windows is to control the humidity levels in your home. This can be done by increasing your homes ventilation and air circulation, running a fan in the kitchen and/or bathroom when cooking or bathing, and making sure your basement is well drained and protected against excess moisture.
It is a common occurrence to initially experience condensation after new windows have been installed. This is because new windows are sealing in the humid air, where before with older less efficient windows the humid air would escape, or more cold dry air would be allowed into your home.
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