Help for drying up your wet winter windows
Cold weather always brings the same puzzling questions to many Canadians from coast to coast. “Why is there condensation on the inside of my windows, and what can I do to make it go away?”
Wet windows are one of the more confusing home management issues because the cause isn’t immediately obvious, nor is the solution. Wet windows not only lead to ugly mould growth, but they’re actually an indication of poor indoor air quality, too. It’s something you need to deal with.
Windows form condensation when indoor air near the window glass cools to the point where it can’t hold all of its moisture any more. e ability of air to hold water is relative to temperature (that’s why they call airborne moisture levels “relative” humidity). When indoor air in your home cools as it comes close to cold window glass during winter, the ability of that air to hold moisture decreases. If cooling happens enough, relative humidity of the air right next to the glass rises to 100 per cent and water droplets form and grow on the glass as the air loses its grip on some of its moisture. When droplets of condensed water get big enough to run down the glass, water pools on the window sill and causes a mess.
While it’s true that the ultimate solution to the wet window problem is to simply lower the humidity in your home, that’s easier said than done in winter. A drier home also brings health drawbacks for some people, too.
So if higher-than-ideal humidity levels are responsible for wet windows, is a dehumidi er the solution? No. Besides making noise and using a fair amount of electricity, dehumidi ers can’t reduce indoor humidity levels enough to solve the wet-winter-window problem. ey also don’t freshen the air, they just take out some of the moisture.
Increasing household ventilation is the best way to reduce window condensation during winter because outside air gets quite dry as it comes inside and warms up. is is why the leaky old houses that used to be so common years ago never had running window condensation. Natural ventilation kept indoor humidity levels low automatically.
e challenge for us modern people is that we want clear windows and fresh indoor air, but we also want to retain the heat energy we invested in the air in our house. Allowing us to have our cake and eat it too is why heat recovery ventila- tors were invented back in the 1970s. is Canadian invention uses fans to send stale air out of the house and bring fresh air in, all while retaining most of the heat energy from the outgoing air stream.
ere isn’t a window condensation problem anywhere in the country that can’t be solved by the installation of a properly functioning HRV. e challenge is cost. You’ll pay about $2,000 to have an HRV installed in your home, but drying out windows might not come to that. Some people have success running bathroom and kitchen exhaust fans more often than usual. is does result in more heat loss from the house, but it can also solve the wet window problem without the need for an HRV.
One of the challenges in all this is nding a level of ventilation and indoor humidity that’s dry enough to keep window condensation at non-damaging levels while also being humid enough for comfort. Unfortunately, most windows today require drier- than- comfortable humidity levels to remain damage-free during the coldest weather. My rule of thumb is to ventilate enough to prevent running condensation, but not necessarily to keep windows 100 per cent dry. is is enough to keep windows in good shape and your indoor air quality fresh and healthful.
Wet wintertime windows like these indicate indoor humidity levels are too high, and indoor air quality isn’t what it should be. Increasing ventilation solves both these problems.