Window Energy Performance Guide
Understanding ER ratings, U-factor, SHGC, and ENERGY STAR requirements for Canadian climates.
Understanding Window Energy Performance in Canada
Selecting energy-efficient windows is one of the most impactful decisions for Canadian homeowners and builders. This guide explains the key performance metrics used in Canada.
Energy Rating (ER)
The Energy Rating (ER) is a single metric developed by Natural Resources Canada that balances heat loss, solar heat gain, and air leakage into one number. Higher ER values indicate better overall energy performance. Windows must achieve a minimum ER of 25 to qualify for ENERGY STAR certification in most Canadian climate zones.
U-Factor
U-factor measures a window's resistance to heat transfer. Lower values are better. Canadian ENERGY STAR requirements specify maximum U-factors that vary by climate zone (Zone 1 through Zone 3).
Solar Heat Gain Coefficient (SHGC)
SHGC measures how much solar radiation passes through the glass. In colder Canadian climates, higher SHGC values can be beneficial — they allow passive solar heating. In mixed climates, lower SHGC values reduce summer cooling loads.
ENERGY STAR Zones
Canada is divided into three ENERGY STAR climate zones: Zone 1 (temperate, southern BC coast), Zone 2 (mixed, most of southern Canada), and Zone 3 (northern, harsh winters). Each zone has progressively stricter requirements.