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Windows and Walls

Buying Windows

Get energy efficient windows for see-through savings

If you're considering new windows, it really makes sense to look for your best options in energy efficiency.

The efficiency of a window is measured by the Energy Rating (ER) which takes into account:

The size of the window
The performance of the glazing
The frame construction
The spacers

A window's ER is expressed as a number. It's based on how much heat comes in, how much heat goes out, and the air leakage of the window.

A negative ER number means that the window loses more heat than it gains. Some operating windows (windows that open and close) have a negative number because there is always some air leakage. However, some windows have a positive number since they actually contribute heat to the house by taking advantage of solar energy, and by having excellent frame designs.

Don't settle for standard windows
The following chart shows you how much more you could save over 20 years if you take the extra step and install Low E Argon windows rather than standard windows.

This comparison is based on an average 121 sq. m. (1300 sq. ft.) electrically heated home with 17 sq. m. (185 sq. ft.) of windows. Your savings would vary depending on your heating fuel source, the cost of local hydro, the actual size and geographical location of your home. These numbers serve as a guide only.

Single glazed windows typically have an ER rating of -50 which is very inefficient.
Standard double glazed windows have an ER of about -30. That's better but not great.

Look for low-e and/or argon gas
Double glazed Low-Emissivity or Low-E windows, especially those that are Argon gas filled, have ratings of -10 to +4 and above.

Low-E, glass prevents the heat inside a room from escaping. The Low-E coating also filters out most of the damaging ultra-violet sunlight, which helps to reduce fading of furniture and drapes.

Highly efficient windows use argon gas to fill the space between panes of glass in double and triple glazed windows. The gas has a higher insulating value than air.

Going window shopping? Here's what to look for on the labels
When it's time to buy windows, be sure to look for the CWDMA label. The CWDMA Certification Program is based on rigorous product testing. The tests include air tightness, water tightness, and wind load resistance. Manufacturers also undergo an in-plant quality control program before certification is awarded.

The labels are packed with useful information. Here are the important facts and figures:

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