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You probably know that replacing your windows can not only make your home look better but that it can also help you cut your utility costs when those new windows are more energy efficient than the ones you replace. What you may be less clear on is what all those numbers or window ratings mean. Many customers find themselves puzzling over these ratings as they try to compare products.

snowy day windows and fireplace


Not to worry though! Below we have compiled a quick guide to understanding window ratings.

Energy Star Rating

Simply put, when a product qualifies for an Energy Star Rating, it means that it is best in class (typically in the top 15-30% in its category) for energy efficiency. Each Energy Star rated window comes with a removable sticker that tells you its rating, the climate zone for which it’s certified and materials that are used.

Energy Rating

The Energy Rating (ER) is a number assigned using strict criteria by an independent organization to tell the customer how well the window rates regarding solar heat gain, heat loss, and air leakage. The higher the rating, the more energy efficient the window is.

U Value/U Factor

The U Value tells the customer how well the window performs in terms of keeping heat inside the home. This is especially important for homes in colder climates. The U Factor generally ranges from 0.2 to 1.2 and the lower the rating is, the better the window’s performance.


The R-Value is a measure of heat resistance or how well the window works at preventing heat flow. The higher the number in the R-Value, the better the heat resistance.

CR Value

CR stands for condensation resistance. The higher the CR Value of a window, the more resistant it is to having condensation form on it. CR Value works with a scale of 0 to 100. For this rating, it is better to look for a higher number.

Visual Transmittance (VT)

Visual Transmittance refers to the amount of light (and therefore heat from the sun) in the visible spectrum which can pass through the window’s glazing. In the case of the VT rating, a lower number is better because it means that less heat is allowed to pass through the glass.

Solar Heat Gain Coefficient (SHGC)

The Solar Heat Gain Coefficient (SHGC) refers to the amount of heat which is absorbed by the glass and transmitted into the home. This rating is between 0 and 1. The lower the number is, the less heat that is transmitted. In other words, a lower number on this rating means a more efficient window.

With all the various energy efficiency ratings that are given to windows, it can be confusing for a customer to know which windows are best for their home. Hopefully, this guide will prove useful as you make your choice. Of course, for more personalized help, the team at Jans Awning Products in Burlington, Ontario is always happy to answer any questions you may have!

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