01/03/2020
Does condensation build up on the inside of your home’s windows during the heating season? If it does, you’re not alone. Winter window condensation is a growing problem in Canada and its root has a surprising origin.
As homes are sealed better against air leakage, natural ventilation to the outdoors is reduced. As a result, indoor air becomes much more likely to contain damaging levels of moisture during winter.
If your windows sweat enough during the heating season to require periodic wiping with a towel, then you have a problem. And this problem goes beyond ruined window-frame finishes and mould growth on windowsills. It includes the very real potential for decay within wall cavities and attics, too. Window condensation can also be a sign of low indoor-air quality which affects your health.
Where the water comes from
When warm, moist indoor air meets the cooler surfaces of windows during winter, condensation develops on the glass. It’s the same thing that happens on the outside of a drinking glass filled with a cold beverage on a hot summer day.
Flaws in your home’s vapour barrier (and there are bound to be some in every home) can allow warm moist air to seep into internal wall cavities, condensing there as it did on your windows, and creating a perfect breeding ground for hidden moulds, fungus and other nasties.
Breathing, cooking, showering and drying clothes all release huge amounts of moisture into the air. In the good old days, this moisture would make its way outside through all the cracks that were once common around windows and doors. That’s why old, leaky houses are often so dry during winter with no window condensation at all.
While today’s homes mean lower energy bills, they also demand that we consciously provide some sort of fresh air to vent off all that water vapour. Boosting home ventilation is the key to solving the window condensation problem.
Open windows a little
This approach is about as easy as they come. Yes, opening windows will cost you a bit more in heating, but it still may be the cheapest way to solve your moisture problem.
Use exhaust fans and proper venting
Bathroom exhaust fans, in particular, should be used during every shower or bath and for at least 15 minutes afterwards.
Installing an exhaust fan in high-moisture areas of your home can help if you continue having minor condensation problems even with your windows opened.
Dryers that vent indoors spew massive amounts of moisture into your home. Proper outdoor venting of your dryer could solve the whole problem.
Install a heat recovery ventilator (HRV)
Although this option will cost $2,000 to $2,500 installed, it will fix the problem once and for all. It will also retain most of the heat that you’d normally lose through open windows and out of exhaust fans. In fact, HRVs are so effective and energy efficient that they’re now required by code for new houses in some jurisdictions.
HRVs incorporate fan ventilation with a built-in heat exchanger that typically extracts 75 to 85 per cent of the heat out of stale indoor air before exhausting it outdoors. This saved heat is then transferred to a fresh stream of air coming into your home from outside.
Opt for better-insulated windows
The higher the R-value of a window, the better it can handle humidity and keep condensation from forming. Triple pane windows, for instance, are much less likely to form condensation than double-pane, all else being equal.
Replacing your windows with ones that have better sealing, but the same insulation value as the original ones, can actually increase window condensation because the new windows reduce air leakage and natural ventilation.
