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Preventing condensation in cold weather

Preventing condensation in cold weather

In Quebec you never know in advance what the winter will bring.

Some winters are very cold and even when your house is equipped with a good ventilation system it is possible that signs of condensation such as the formation of ice at the bottom of the windows appear. According to the Association provinciale des constructeurs d’habitations du Québec (APCHQ) it is possible to avoid this problem.

Hot and cold


Before questioning the quality of the windows in your home you should know that air is a gas which, depending on its temperature, may contain more or less water vapor. The more the air is warm, the more it can hold water vapor without creating a problem.

The glazed windows do not fog up during the summer when it is 30°C and when the relative humidity is 95%. Why? Because, when a gas is heated, the molecules are distancing themselves from each other and leave more room for steam. The same principle applies during the winter: at a given temperature, say -4°C, the air can contain 50% moisture.

But when the temperature drops quickly it cannot contain the same amount of steam anymore. The relative humidity is thus soaring and so the surplus steam is then deposited on the glass. The phenomenon is accentuated if the window frame forms a tablet depriving the bottom of the window of the heat.

How to prevent condensation?


When the moisture content does not follow the curve of the drop in outside temperature it is almost inevitable to see condensation appear. To avoid this problem, the relative rate of humidity of the indoor air must therefore follow this curve. Through simple actions you will help to optimize the operation of the ventilation system and reduce condensation on the windows of your home.

Limit the number of plants that decorate your home, make sure your dryer is well connected, avoid lowering the temperature inside or storing your firewood in the basement. Activate the kitchen and bathroom fans during and after each use, taking care not to unduly prolong the showers. The ventilation grilles should be located in the right places and should not be obstructed to operate at full capacity.

Also, if this is not already done, remove the mosquito screens from your windows and refrain from closing blinds or fabrics during the evening, which will allow the heat from the heating system to warm the glass.

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Québec Landlords Association

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