Since regional climate conditions have an impact on the type of window you need, the ENERGY STAR^® program has geographic zones that correctly identify the products that you need. See our ENERGY STAR^® calculator.

The most important number on the rating sticker is the Energy Rating (ER). This measures a window’s overall energy performance and efficiency, taking into account the insulating capacity, air-tightness and solar gain (the extent to which a window heats up in sunlight). The higher the ER the better and ratings range from 0 to 50. The most energy-efficient windows in Canada have ERs in the low 40s and are generally triple-pane windows. Double-pane windows max out in the low-to-mid-30s.

The U-Factor measures how well the window prevents heat from escaping. U-Factor ratings generally fall between 0.20 and 1.20 and the lower the U-Factor, the better the window is at keeping heat in. The U-Factor shown on the label is based on a whole-window rating system that takes into account the different U-Factors of the window’s frame, sash, edge of glass and centre of glass. In Canada, where heating bills are a major concern in the winter, selecting a window with a lower U-Factor will reduce the amount of heat that escapes through a window from the inside of the home to the outside.

The SHGC measures the rate of heat gain through a window or how well the window blocks heat from the sun. The lower the number, the better the window is at blocking solar heat. In the summer, where air conditioning bills rise, choosing windows with lower SHGC will reduce the amount of heat that comes in through your windows from the outside.

The visible transmittance measures how much light comes through a window and is expressed as a number between 0 and 1. The higher the number, the more daylight comes through the window.