How to Prevent Condensation and Ice Buildup on Your Windows

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The first week of February 2023 has been extremely cold in Ottawa, with the wind chill making it feel colder than -42.

With temperatures this low, more and more homeowners started seeing condensation and/or ice build up on the inside of their windows. Naturally, owners started wondering if this was normal at all.

We have prepared a short guide to address these concerns. Hope you enjoy the article below!

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First of all, is it normal to see condensation on windows?

Up to 1″ of condensate on all sides of the window is considered normal, especially if the outside temperature is below -20. If your windows are getting completely frosted over, it might be a sign of a bigger problem.

What Causes Condensation on the Inside of Windows?

Superficial condensation occurs when the surface temperature of a solid (glass, sash, frame) is lower than the dew point of the humid air in its immediate vicinity (Source: NRCAN)

In simple words: when warm & humid air meets a cold solid surface, condensation occurs. In case with window condensation, humid air from inside of your home meets the cold glass, and you see condensation on your windows.

How to Get Rid of Condensation Inside Windows?

While completely eliminating condensation might be hard to achieve, there are ways to control it. First, condensation can be decreased or eliminated by raising the inside surface temperature and, second, it can be changed by adjusting the relative humidity of the indoor air (Source: ibid)

How to Prevent/Reduce Condensation

Reducing or eliminating condensation often means using several complementary techniques.

These techniques concern the window itself, the method of installation, the interior window accessories (curtains, blinds, and valances), the arrangement of heat sources (hot air registers, baseboard heating, convection heaters) and the relative humidity of the indoor air.

The overall condensation resistance of a window depends on each of these factors (Source: ibid).

For the purpose of this article, we will focus exclusive on factors that are within homeowners’ control, i.e. relative air humidity and air flow.

Unimpeded Air Flow

To maintain the condensation resistance of the window, interior window accessories such as curtains, blinds and valances must not inhibit or impede the movement of air at the surface of the window.

Any restriction of air movement will reduce the condensation resistance and thus increase “sweating” on the window (Source: ibid)

In simple words: lift up the blinds by at least 2 inches to allow for air to flow freely and ventilate the window. Remove window blinds, curtains, or in general anything that obstructs the flow of air.

Arrange Your Heat Sources Correctly

Although energy-efficient windows are now available, the heat loss through them is still greater than through the adjacent walls.

This is why windows with heat sources located below them are less prone to condensation. When the heating system is in operation, the air temperature will be higher in the vicinity of the window than in the centre of the room, resulting in increased condensation resistance.

Care must nevertheless be taken to ensure that the hot air from the registers does not flow directly onto the interior surface of the glass, as this could give rise to thermal stress problems in the glazed unit that could cause the glass to break (Source: ibid)

In simple words: If you have a heat source that blows hot air directly onto the window (such as additional heaters), position this heat source away from the window or else the window might crack. Ceiling fans usually help air circulation and you might want to keep them on for a better air exchange.

Control the Relative Humidity of Indoor Air

The concept is very simple: the less humid the air inside is, the less water will condense on the windows.

This, however, is often easier said than done: living habits and the production of humidity in the house (showers, baths, cooking activities, plants, etc.) remain unchanged, and there is a significant reduction in the rate of air exchange, the resulting relative humidity at certain times during the winter may become excessive and cause condensation on the inside surface of new windows.

Reducing the amount of humidity in the house may enable you to limit or eliminate the problems caused by humidity.

How to Reduce Relative Humidity of Air in the House

• If your heating system is fitted with a humidifier, or if you use portable humidifiers, disconnect them.

• Avoid hanging laundry inside to dry, and make sure that the exhaust from the clothes dryer is vented outside.

• If you have a crawl space under your house, cover the beaten earth with 0.15 mm (6 mil) polyethylene. The crawl space may have to be ventilated during the summer.

• Make sure that your basement is well drained and protected against excess moisture. Also, make sure that gutters and the slope of the land around the house drain water away from the house.

• Try not to produce too much humidity. Plants, laundry, showers and cooking without lids are major sources of water vapour.

• Avoid drying firewood in the house. A cord of wood can release more than 270 litres (60 gallons) of water.

Indoor Relative Humidity Levels to Prevent Condensation

Outside Air Temp (°C)Max Indoor Relative Humidity at 20 °C
-30°C or below15%
-30°C to -24°C20%
-24°C to -18°C25%
-18°C to -12°C35%
-12°C to -0°C40%

Lowering relative humidity in your home should have limits, however. If it gets too low, air will get too dry, which will significantly reduce the comfort of your home, causing itchy eyes, scratchy throat, and dried-out mucus membranes.

The main takeaway therefore is to find a good balance between the comfort in your home and an acceptable level of condensation on the windows. If temperature drops are temporary, you might want to adjust relative humidity inside of your home, but it has to be reasonable.

My Windows Didn’t Pass the Test of Cold, What Do I Do?

Identify the root cause of such low performance. It could be that the window itself is decent, but it has not been installed properly. If it’s the case, you can get just have the window properly re-sealed/re-foamed and you should be good.

If, however, the window is too old, or the quality is unacceptably low, it might be the time to replace it, and we would be happy to help!

Give us a call or submit a form on this page to request a free quote. Check out the promotions section of our website, you might be able to buy a top-of-the-line triple glazed windows for the price of the double glazed ones, receive a government rebate and get an additional discount from Buildmart!

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