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Condensation on Windows in Winter: Causes and Solutions

Condensation on Windows in Winter

How to Deal with Condensation on Windows in Winter

Condensation on windows in winter is a common problem in Canada. It is as a result of high humidity levels in our homes. Humid air holds water vapor until it comes into contact with a surface whose temperature is lesser than or equal to the Dewpoint, (a temperature at which air becomes saturated with water vapor and produces dew). Glass surfaces are usually the coldest parts of a home because of their low R-value (Resistance to heat flow) . Condensation on windows in winter time appears first because of this, generally in the form of water droplets or frost on the room side of the window. As interior air becomes dryer or as the glass surface becomes warmer condensation begins to dissipate.

Sweating Windows in Canada

How to Prevent Sweating Windows

Canadians love their windows. Who would not, if you consider the aesthetical appeal they add to homes and the scope offered in terms of dressing them. So much research and innovation have been invested to enable them to sync in with the extremes of climate. In winter most Canadian homes, windows become a cause of concern. As temperatures begin to plunge to freezing point or below, the condensation of water vapor on them becomes a nagging thought, and an alarm is raised for help when ice begins to appear around window panes. Why it happens is common knowledge and the fact that it cannot be avoided in today’s energy efficient and ‘tightly’ insulated homes is convincing enough. Brushing up one’s skills on keeping humidity levels in the home within the prescribed limits is what poses the challenge.

#1. What Causes Windows to Sweat From Inside?

The Canada Mortgage and Housing Corporation conducted surveys on several types of houses to find out the cause of condensation in homes. Following reasons cited are:

  • Too much moisture in bathrooms from hot baths and showers.
  • No bathroom fans or even if available not being used.
  • Uninsulated fan ducts.
  • Leaky plumbing and plumbing leaking through walls.
  • Dampness from wet bath mats, towels, and drying clothes.
  • Inadequate ventilation.
  • The temperature kept low.
  • Uninsulated vent ducts. Uninsulated toilet tanks. Backdraft damper on fan housing inadequate.

#2. Preventing Window Condensation-

Interior temperature and relative humidity are personal preferences in one’s own home, but exceeding recommended humidity levels for extended periods of time can lead to a high risk of condensation problems.

The relative humidity level varies between winter and summer and by location. As a rule of thumb, the interior air temperature should generally be maintained at 18 degrees C and 24 degrees C with Relative Humidity falling between 35% and 60% for the coastal temperate climate regions of British Columbia during the winter months. In the colder and drier parts of the Province, the interior humidity levels should be limited to 25% and 40% during winter months.

Long and careful experiments at the University of Minnesota Engineering Laboratory shows the maximum safe humidity levels for a home, not only for windows but even more for paint, insulation, and structural members. In most cases, reducing moisture to these humidity levels will cure troublesome condensation on windows in winter. For high temperatures, lower humidity levels are required.

#3. Maximum Recommended Humidity Levels-

Outside Temperature Inside Humidity:

(70 degrees F indoor temperature)

20 – 40 F not above 40%

10 – 20 F not above 35%

0 – 10 F not above 30%

-10 – 0 F not above 25%

-20 – -10 F not above 20%

-20 F or below not over 15 %

If you are unsure of humidity levels in your homes, a device called Hygrometer will allow you to measure humidity levels in your home.

The CMHC advises that keeping Relative Humidity low enough, at 30% usually, will help to avoid condensation on windows in winter.

#4. How Do I Avoid Condensation Problems-

Between January and March 1988-94 homes across Nova Scotia, Canada of different sizes, ages, and styles with reported moisture problems were inspected. Nova Scotia has a cold, windy, and humid weather nearly all the year round with little or no drying season. Poor ventilation and high moisture generation from stovetop boiling, wood stored indoors, showers, leaky or wet basements or crawl space, unvented clothes dryers, kerosene heaters and furnace humidifiers. Condensation and moisture damage was most common on window sill, trims and frames at outside wall corners, on ceilings in closets, in bedrooms and attics.

Ventilation improvement was the most often recommended method of resolving the moisture problem. Condensation problems can be avoided in our homes if we reduce the amount of moisture or humidity generated in our homes, promote good air circulation in our homes and promote good ventilation in our homes.

Installing a Heat Recovery Ventilator (HRV) is now required by code for new houses in some jurisdictions of Canada. It incorporates fan ventilation with a built-in heat exchanger that typically extracts 75% – 85% 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 the home from outside. HRVs facilitate ventilation while retaining most of the heat that would be lost through open windows and exhaust fans.

The Energy Star name and symbol are administered and promoted in Canada by the Natural Resource Canada and are registered in Canada by the US Environment Protection Agency. Because humidity levels are normally higher in bathrooms, kitchens and laundry rooms installing appropriate Energy Star labeled products in these rooms like exhaust fans and dehumidifiers reduces or eliminates condensation on windows.

#5. Window Treatments Can Increase Condensation on Windows-

Condensation on windows in winter will often occur where shades or draperies are closed because most window treatments separate the cold glass from the warm room air allowing the glass to cool further below the dew point temperature. Condensation, in such a case, can be prevented by covering the window with a tightly sealed interior moveable insulation or prevent condensation from building up by opening the treatment during the day.

Interior window accessories such as curtains, blinds and valances must not prevent air from moving around the surface of the window. Any restriction of air movement will increase condensation on windows.

Custom-Roman-Shades-Canada -


Suitable Window Treatments Ideas for Condensation Problems

Karla. J. Neilson in her book, WINDOW TREATMENTS, says that one of the most effective and commonly used window treatments that can tackle the condensation problem on windows is a fabric shade whether Flat Roller Shade or Custom Fabric Roman Shades in Canada.

Crown Blackout Roller Shades is made from 4 ply vinyl material, a combination of 1 ply Fiberglass and a 3ply Vinyl. These strong and durable shades are washable and are a great insulator for the summer and winter, besides blocking 100% UV rays.

Blackout Roller Shades for Windows

The Crown Light Filtering Roller Shades are made of finely woven polyester with a crisp fall. Optimum diffused light can enter the home without an invasion of your privacy. Cordless Loop Control and the cordless option makes the operation of these shades easy.

Light Filtering Roller Shades

LightWeaves Graber Roller Shades made of a Polyester and Vinyl fabric gives them the much-needed endurance. A backing of Acrylic, Cellulose, and Cotton helps in enhancing the light control capabilities of this shade. The Cordless Lift system and the SmartLift system add to its style.

Artisan Roman Shades

LightWeaves Graber Blackout Roller Shades give 100% darkness when lowered. Cordless Motor option that works on RF helps in operating these shades from any place in your home for an easy control.

Norman’s Centerpiece Roman Shades are available with light filtering and room darkening options. It has an Aerolite Cordless System for child and pet safety and a safety tension device for the Continuous Cord Loop ensures complete safety. They are available in eye-catching colors and a standard white lining for Room Darkening option.

Graber’s Artisan Roman Shades are designed with mitered corners and double turned hems. It is available in the Classic Flat, Balloon, Seamless, Relaxed and Looped styles.



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1 thought on “Condensation on Windows in Winter: Causes and Solutions

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