Did you know that extreme winter cold can place undue stress on your house? Consider your windows. A graphic example of the effects of extreme cold can be seen on the old single-glazed, metal-framed windows in many older homes. Over a really cold night, these windows will often frost right up. While wonderfully artistic, and fun for kids to scratch their names into, this does render the window particularly useless: can’t open it – frosted shut; can’t look out – frosted over…

Windows all over the province will be exhibiting varying degrees of the same effect. Even some new windows will sweat heavily or frost up. Let’s look at the root causes, and suggest some solutions.

Whence the Water?

You likely understand that the water forming on the window is due to the condensing of moisture in the house air. Vapour droplets in the air that come in contact with the cold surfaces of the window will, IF – and this is key – the surfaces are cold enough, cool down into water droplets and precipitate onto the cold surfaces. If this happens all night long, there can be considerable accumulation of water. In some cases, the water drops freeze shortly after forming on the window, causing ice to build up.

Waylay the Water

How can the problem be corrected? Two ways: remove the moisture in the air in the house, and warm up the interior temperature of the window glass and frame.

Let’s look at both strategies. First, remove the moisture in the air. Good luck. Since you and your pets live in there, and you all do things that create moisture (not the least of which is breathe) we can’t eliminate the moisture. The best we could hope for, short of moving to Arizona, is reducing the interior air moisture level to a minimal level. Do this by turning down or off your furnace humidifier, ensuring your clothes dryer is venting properly, using kitchen and bathroom exhaust fans when cooking and showering, and opening a window periodically when things feel “stuffy”.

But you can only go so far, and if your windows are cold enough the sweat will still form. In my bedroom, over the course of the night, my wife’s and my (and various of my kids’ at any given time) respiration is the only moisture source. But my old windows are the worst possible design for avoiding sweat. Of course, it’s the same as the dining room window, so why not there?

That’s the second strategy: warm up the surface temperature of the window glass and frame. If the window is old, it may be drafty. This will be apparent in cold air whistling through around the edges. Luckily, replacing or improving weatherstripping, a relatively easy DIY project, can often solve a draft problem. If the room has only one pane of glass between it and the outside, install a storm window. This will warm up the interior pane. Of course, the frost may simply form on the inside of the storm window anyway. With a newer double-glazed window, unless it’s very cheap or very poorly installed, the glass and frame temperature should be pretty reasonable.
The trick now is to assess where the heat source is in the room. In a perfect world, the heat for the room is delivered at floor level right below the window. The idea is that the warm air, either from a furnace register or convecting off a radiator, washes up the window, keeping the glass and frame nice and warm, reducing or eliminating condensation.

A related problem in many homes is the window treatments. California shutters look great and can block out light, but when closed they also block warm air from reaching the window, leading to condensation in cold spells. The solution is to open up the louvers, or open the shutters. Many blinds and drapes have the same effect. When closed, find a way to prop them out at the bottom so that the warm air can go up between them and the window.

If you’ve tried everything, and still you have a window or two that sweat uncontrollably, the low-rent hardware store plastic sheeting will work nicely. This remains the cheapest solution for your windows. A better, but more expensive solution? Replacing those old windows with new multi-glazed coated windows.