In Windows & Doors

energy starAs the country becomes more environmentally aware, measurements such as energy ratings become more important during the purchase process. Windows have a rating system for energy performance that’s tested against Canadian Standards Association (CSA) guidelines. However, for the uninitiated, understanding these ratings is far from straightforward. In an effort to help with understanding window energy performance ratings, we provide this guide.

Energy Star Certification

The North American Energy Star certification system was created to take a lot of the mystery out of individual energy ratings. The appearance of the Energy Star logo tells the consumer that the product meets energy efficiency standards. That said, even among products with Energy Star certification there are varying degrees of energy efficiency. That’s why it’s important to understand the various individual ratings.


The U-Factor measures the amount of heat that can be lost through the window. This is expressed as a value ranging from 0.20 to 1.20. A lower U-Factor means the window is better at retaining heat.

Solar Heat Gain Coefficient (SHGC)

The SHGC measures the amount of heat that is allowed to enter a window from the outside. This will range from 0 to 1 with a lower number indicating a lower amount of heat being able to enter into the building.

Visibility Transmittance (VT)

VT measures how much visible light is able to pass through the window. It also ranges from 0 to 1 with a lower number meaning less light from the visible spectrum is able to penetrate the window. A high VT rating combined with a low SHGC rating often means more of the useful visible spectrum of light is able to penetrate the window while less useful light from invisible parts of the spectrum is blocked.

Air Leakage

Air leakage ratings range from 0.1 to 0.3 with a larger number meaning more air leakage and therefore more air being able to pass through the window. If you’re looking for energy efficiency you want a low air leakage value.

Energy Rating

The energy rating takes into account the U-Factor, SHGC and Air Leakage ratings to create a composite energy efficiency score for windows. A higher energy rating means a more energy efficient window. Depending on the climate zone you live in, a minimum rating ranging from 25 to 34 should be sought after.

Book a consultation with Comfort Doors and Windows to get started.

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