Two workers installing windowsThe National Fenestration Rating Council (NFRC) rates ENERGY STAR–certified windows in Salt Lake City, Phoenix, Atlanta, or anywhere in the United States. The primary goal of this non-profit is to measure how well each unit can help reduce the heating and cooling costs of American households. Its ratings don’t necessarily say which products are good or bad but. Rather, they determine the most suitable windows for different areas based on the requirements every climate zone has.

Here are the usual ratings you’ll find in the NFRC label:


This refers to the insulating quality of the window. The U-factor is expressed in a number between 0.20 and 1.20. The lower the value means, the better the unit at keeping indoor heat from escaping the room.

Solar Heat Gain Coefficient

This rating measures the ability of the window to block unwanted infrared light from the sun. It’s expressed in a number ranging from 0 to 1; the smaller the value, the more effective the unit is in keeping solar heat out.

In many cases, the maximum U-factor the climate zone accepts dictates the minimum Solar Heat Gain Coefficient value. Be aware of the optimum combination of ratings in your county to separate high-performance windows from less efficient ones.

Visible Transmittance

It measures the ability of the window to enhance daylighting. Also expressed a number between 0 and 1, the higher the rating means, the better the unit is at illuminating the interior. Windows with a high Visible Transmittance rating can reduce your dependence on artificial lighting. Also, they help keep your rooms cool since traditional bulbs produce more heat than light.

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Air Leakage

This rating determines how much air can pass through the window. Expressed in a number between 0.1 and 0.3, look for the lowest value to avoid expressing unwanted drafts. Plus, products with stellar air-leakage rating helps prevents your heated or cooled air indoors from going out.

The NFRC label may be small, but its message is big. Read it first to help you narrow your best replacement window options down.