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Understanding Window Ratings


Understanding window ratings.

This is a NFRC window label.

U-Factor measures how well a product prevents heat from escaping a home or building. The lower the U-Factor, the better a product is at keeping heat in. Particularly important during the winter. Solar Heat Gain Coefficient measures how well a product blocks heat from the sun. The lower the SHGC, the better a product is at blocking unwanted heat gain. Particularly important during the summer.
Visible Transmittance measures how much light comes through a product. The higher the number, the higher the potential for brighter light. Air Leakage measures how much outside air comes into a home through a product. The lower the number, the better the product is at keeping air out. This is an optional rating and some manufacturers choose not to report it.
Condensation Resistance measures how well a product resists the formation of condensation. The higher the number the better. Another optional rating some manufacturers choose not to report.

How to read the labels. Understanding window ratings

This is an NFRC door label. Notice that the energy ratings (u-value and SHGC) change depending on amount of glass the door has and the type of glass. Please click picture to open a large version pdf.