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Winter Condensation on Your Windows

Why it’s there and what you can do to minimize it

If you’ve just replaced old, leaky windows with new, more energy-efficient windows, you may notice something new when cold weather hits; condensation. Rather than being a defect, condensation actually means that your new windows are protecting your home more than your old ones were. But there are ways to minimize it if it is a concern.

How does condensation happen?

Condensation is moisture created when warm air hits a cold surface. Since your windows are more likely to be cold than your walls, you’ll notice it first on your windows. Condensation is less likely to happen on older, leaky windows because air will pass through the windows before it can start condensing on the surface of the glass.

How can I reduce the condensation?

Condensation should be reduced to prevent minor water damage to the bottom of the window and the interior wall underneath it. The best way to reduce condensation is to be mindful of the amount of humidity in your home. Kitchen and bathroom fans should be installed if they don’t exist already, and you may want to consider cracking a window just after cooking or a shower, the two activities that tend to encourage condensation. If it is too cold to do this, run your kitchen and bathroom fans a bit longer than you were used to doing.

If condensation continues after taking these smaller steps, consider purchasing a dehumidifier and using it either as part of your central heating system or in the areas affected most by condensation. Excess humidity in the home doesn’t just take a toll on your windows - it can encourage mold and other indoor air pollutants, so you should fix it if you notice it. Both Health Canada and the Canadian Mortgage and Housing Corporation recommend a 30% relative humidity level inside during the winter, and 50% during the summer. If you find 30% too dry, you can go up to 50%, but monitor the amount of condensation on your windows and be prepared to wipe it up if you get more. You should also check that ventilation fans in your bathroom and kitchen are being ventilated to the outside, and not to an attic space where mold can become a problem.

Extremely cold weather will bring on condensation even if your home has perfect humidity. If you just notice condensation on extremely cold days, don’t worry about it as it is a short-term problem that will only occur when it is way past the point where you want to go outside. If you want to reduce the risk of condensation when the exterior temperature dips below -25 Celsius, reduce the humidity in your home to between 20-25%. Give the bottom of your windows a quick wipe on extremely cold days to prevent mold from forming.

If you get mold on your sills or anywhere else from condensation

Wipe it up with white vinegar. This will effectively kill the mold and keep it from damaging your interior surfaces. Don’t worry about purchasing any fancy anti-mold and mildew products; white vinegar is the tried-and-true solution.

Can special kinds of windows reduce condensation?

A better window will actually have more condensation, not less, due to more precautions by the manufacturer to make the window airtight. The answer does not lie with a different window, but by controlling humidity levels in your home and not “sweating” it on extremely cold days when you see a bit of condensation.

When is condensation a problem?

If you see condensation between panes of glass in your windows (in the interior of the window itself), this can indicate a seal failure. If you purchased your windows from us, call us for a service call if you notice this. If we didn’t sell you your windows and you have interior pooling inside the window, you may want to consider replacing them as this means a loss of seal integrity and energy efficiency.