Energy-Efficient Residential Windows, Doors and Skylights

Ratings and certification

Energy efficiency ratings

Windows, doors and skylights are tested using standard sample sizes to fairly rank their overall structural and energy performance. In Canada, the testing of windows, doors and skylights for their energy performance is not mandatory except in Ontario and, beginning in 2009, British Columbia. The values that are most often used in Canada to portray the energy performance of windows, doors and skylights are the following:

• U-value: Indicates the rate of heat transfer from warm to cold areas in watts per square metre Kelvin (W/m²•K). The lower the value, the slower the rate of heat transfer.
• R-value: Indicates the resistance to heat transfer in square feet per hour in Fahrenheit temperature per British thermal unit (sq. ft.•h•°F/Btu). The higher the number, the higher the resistance to heat transfer.
• Solar heat gain coefficient (SHGC): A ratio indicating the amount of the sun's heat that can pass through the product (solar gain). The higher the number, the more the solar gain.
• Energy rating (ER): For windows and doors only, this unitless number  reflects the balance between heat transfer (U-value) and solar gain. Higher numbers indicate a slower heat transfer without significantly reducing the amount of solar gain. 
• Visible transmittance (VT): A ratio that indicates the amount of visible light that can pass through the product. The higher the number, the more visible the light that can pass through.
• Centre-of-glass: Often called "centre-of-glass ratings," these values make the product appear more energy-efficient than it really is, because the values are not for the whole product, only the glass portion.

Structural ratings

Building codes in Canada require that all windows and sliding glass doors be rated for their structural performance when they are installed in new homes or buildings. Provincial, territorial and local building codes require different minimum ratings, depending on the climatic conditions. The following tables show the different structural performance ratings and their ranges.

* The operable and non-operable sashes may be tested and rated separately for single-hung and single sliding windows.

*This test measures only how well the screen mesh stays fastened to the screen mesh frame, not how well the insect screen stays fastened to the window frame. Most insect screens can be easily removed from the window to allow for exit in an emergency. An S1 rating is adequate for residential applications.

Certification

Certification ensures that the testing is done by an accredited laboratory against the current standards and that the results have been verified by an independent third party. Certification also helps to ensure that no unauthorized changes have been made to the certified products that would change their quality or performance ratings. Windows, doors and skylights sold in Canada may be certified for their energy performance by the following accredited agencies:

• CSA International
• Intertek Testing Services
• Quality Auditing Institute Ltd.
• The National Fenestration Rating Council (United States)

The IG units may also be certified for their durability by the Insulating Glass Manufacturers Alliance (IGMA). This certification program tests a manufacturer's ability to build a unit that will not fog or have premature seal failure and that will gas-fill units properly and consistently.