While you can feel confident in buying a window with an Energy Star label, if you want to really know what you’re getting in your windows, the Canadian Standards Association has established the CSA A440 standard that applies to all windows sold. See how your windows measure up according to these specs.
A U-value indicates the rate of heat transfer. The lower the U-value number, the slower it transfers heat from a warm area to a cold area. Equivalent R-values have been given to help you understand the U-values. An R-value is the inverse of a U-value and indicates the resistance to heat transfer. The higher the R-value number, the more insulative the product is. Neither the U- or R-value account for heat energy from the sun (solar gain).
ENERGY RATING (ER)
The Energy Rating (ER) value is calculated using a formula that balances a product’s U-value with its potential solar heat gain coefficient (SHGC). The higher the rating (from 0 to 50), the more efficient the product.
The ratings are adapted for each zone in Canada, but note that these requirements are changing as of Oct. 1, 2010.
Find out about the upcoming changes to Energy Star requirements as of Oct. 1, 2010. SOLAR HEAT GAIN COEFFICIENT (SHGC)
The SHGC is a measure of solar heat gain and airtightness. It measures how well a window blocks heat from sunlight. It is expressed as a number between 0 and 1. The lower a window’s SHGC, the less solar heat it transmits.
VISIBLE TRANSMITTANCE
Visible transmittance measures how much light passes through a window. High visible transmittance is desirable to get more sunlight on the north side of a home, but not on the east and west sides, where sun is a cause of glare. While it varies between 0 and 1, most values among double- and triple-pane windows are between 0.30 and 0.70. The higher the number, the more light is transmitted.
AIR LEAKAGE
Air leakage (a value between 0 and 1) measures how much air passes through a square foot of window by infiltration through cracks. The lower the better.
WATERTIGHTNESS
How well a window can withstand water leakage from a storm is measured with a rating of B1 to B7. The higher the better.
WIND-LOAD RESISTANCE
This rating measures how well a window will be able to resist window pressure without breaking away from the frame. Performance is shown by a measure of C1 to C5, but a C2 is the minimum for most low-rise buildings in Canada.