Replacement Windows Ratings | Discover 4 Key Indicators


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Replacement Windows Ratings

Replacement windows ratings provide important metrics and numbers that can be used to compare different window brands, models etc. We will go through each of the four main rating factors and explain what you should look for when shopping and purchasing replacements for your home.


This is the level of heat loss associated with different windows. U-factor is a number ranging from 0.2 to 1.3, which indicates how much heat has been lost through the glass or frame of the window. A good window replacement should have a lower U-factor since this indicates that it is energy efficient. Most mid grade vinyl frame will have a U factor around .32, which is a pretty respectable number to shoot for.

Air Infiltration

Also referred to as AI, this rating will generally range from 0 to 0.3. It indicates how much air enters from the exterior to the interior of the window frame and glass. The lower this number is, the better the window since less air is entering the home.

Solar Heat Gain Coefficient

This indicates how much heat is seeping in or out of your home through the glass and/or frame of your windows. SHGC has rating from 0 to 1.0. The rating you want from this category depends on your local climate. If it is generally hot, then a low SHGC is preferred because it means less heat is entering the home. A higher solar heat gain coefficient is better for colder climates because it means more heat is entering the home and helping to keep the house warmer.

Visible Transmittance

VT indicates the level of light passing through the glass of your windows. This ranges from 0 to 1 in the VT replacement windows ratings. Lower numbers means that your window allows less light to pass through.

The Importance of Replacement Windows Ratings

Window performance is mainly indicated in the first three categories (U-factor, AI and SHGC). You will typically want a 0.35 or lower number with U-factor, .1 or less for AI and SHGC varies from one climate to another. You can find a wonderful service at the NFRC website, which allows you to search for different brands and models and get accurate ratings.

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