How to Read an NFRC Window Label

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An NFRC Window Label is a rating sheet or sticker found on every new window. It has four little boxes that show the independent test ratings for the energy efficiency of the glass.

NFRC, the National Fenestration Rating Council, is an independent testing facility that performs energy rating tests on windows, doors, and skylights. The four separate ratings are for:

  1. U Factor
  2. Solar Heat Gain
  3. Visual Transmittance
  4. Air Leakage

U Factor on a NFRC Window Label

The U Factor rating is in the top left corner of the label box, and it shows the level of UV Protection on a window. This number needs to be below 0.3 for the window to have an energy star rating, and lower is better.

The U Factor test number tells you how well the window insulates in general. It’s a good indicator of how much of your warmth can escape in winter, and how much of the cool air inside your home can escape in summer.

Solar Heat Gain

The top right corner of the NFRC label shows the SHGC, or Solar Heat Gain Coefficient. This number indicates how much harmful UV light rays from the sun are coming through the glass and heating up the inside of your home.

This is a good number to know for summertime when you want to keep your house cool. If the window allows too much UV light through, it can make your air conditioner struggle to keep the house at a reasonable temperature.

This number also needs to be below 0.3 for an energy star rating, and again, lower is better. The average is 0.26-0.28. Some of the Joyce windows we install are rated at 0.22.

Visible Transmittance Label Rating

Visible transmittance is how much natural light the window lets through to your home. You want windows that will allow in enough light so that you don’t have to turn on lamps and lighting inside during the day and run the energy bill up.

For that reason, it’s unusual to find home windows that have strong reflective qualities like sunglasses. This level of reflection would block too much natural light from getting inside. Slight reflective qualities keep UV rays out, but allow the natural light to still come through.

NFRC Window Label Air Leakage

The air leakage rating is in the bottom right corner of the label, and this is very important to gauge the energy efficiency of the window. It tells you how much air is passed through the window from outside to in and vice versa.

This number should be at or below 0.3, but the material used on the window influences how much air comes through. Vinyl and Fiberglass windows have lowest air leakage and often have foam filled frames for added insulation. Wood windows can develop bad air leakage over time because wood expands and contracts with heat, cold, and moisture.

Manufacturer Results Vary

Window manufacturers are not required to post the results of their NFRC tests, and many choose not to. The window manufacturers we work with the most, Sunrise and Joyce, make their test results readily available to us. And they have some of the best ratings in the industry. Some of the double hung windows we install are rated at 0.02, which is substantially lower than the 0.3 needed to receive an energy star rating.

Give us a call and we’ll help you decide. We can show you the NFRC window labels for each window we sell while helping you understand how each rating helps in your home.