You might think that all windows are relatively the same, but science and engineering have proven it to be not true. Various styles and models offer you more than others do. To keep this simple the Canadian Standards Association (CSA), has created a rating system so you know exactly what you’re getting when you purchase new windows, doors, or skylights. Here is a breakdown of how their rating system works:
Energy Performance Ratings
U-factor – This is a number that measures the rate of heat transfer from warm to cold areas in watts per square metre Kelvin or British thermal units per hour per square foot Fahrenheit. In both cases, the lower the number is the more efficient the product.
Solar Heat Gain Coefficient (SHGC) – This is a ratio that shows the amount of heat from the sun can pass through the product. Therefore, the higher the number the more solar heat the product gains.
Energy Rating (ER) – This is a value that demonstrates the balance between the U-factor, SHGC and air leakage. The higher the ER number is the more efficient the product. It’s important to note that this value applies to windows and doors but not to skylights.
R-value – This value indicates the resistance to heat transfer in square feet per hour in degrees Fahrenheit per British thermal unit. In simpler terms, the higher the number the more heat resistance there is in the window. It’s important to note that this value is not a part of the energy performance standards, but it is often used by contractors and sales staff as a measure of performance.
Visible Transmittance (VT) – This is a ratio of the amount of light that can pass through a product. The higher the number the more visible light is able to pass through.
Centre-of-Glass Rating – This number represents the energy efficiency value that only refers to the glass part of the window and not the whole window itself.
Physical Performance Rating
Building codes in Canada require that before all windows and doors are installed in new homes and buildings, they must be rated for their physical performance. These ratings are based on minimum air leakage, water tightness, and structural strength. The ratings vary between different provinces, territories and municipalities, and depend heavily on climate conditions.
The standards in Canada are being brought in line to meet that of the North American Fenestration System or NAFS. These standards apply to all windows, doors and skylights. The products are all given a grade based on where they are used:
- R – is for single-family residential buildings
- LC – is for low and mid-rise multi-family residential and light commercial buildings
- CW – is for mid-rise multi-family and commercial office buildings
- AW – is for high-rise multi-family residential and commercial buildings.
These standards are also given a number. The higher the number, the stronger and more water-resistant the product is.
When considering a window replacement, make sure that you’re buying products that meet or exceed these standards. These standards are in place to reduce the impact on our environment, while also allowing you to save energy and money.