Condensation is caused by humid air coming in contact with a cold surface, such as glass. Just like a glass of ice water in warm room, condensation creates many small droplets of water, and becomes visible on the glass surface. This is completely normal, and will occur in every home at one time or another. Everything in your home that involves water will contribute to excess humidity, such as showers, mopping, watering plants, and heating/air conditioning units.
Excessive condensation however, may be linked to a problem with the window, such as:
Although condensation is not completely preventable, there are several methods that can help reduce the problem.
The following chart shows the recommended humidity levels during winter seasons, and you can measure your indoor humidity with a humidistat or psychrometer.
|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.)|
It is also important to remember that sometimes you will see an increase in humidity after you've installed new replacement windows. This is because the seals in your old windows were cracked and drafty, allowing air (and therefore moisture) to escape from your home. Your new windows however, have tighter seals, and are allowing less air to escape outside.