Window
Ratings and Labels
It can be difficult to compare claims made by different
manufacturers, because they often use different measures to sell their products. For
instance, some may use center-of-glass R-value and shading coefficient, while others use
whole-window U-factor and solar heat gain coefficient. Fortunately there is now one place
to look that has standardized ratings for windows. The National Fenestration Rating
Council (NFRC) is a nonprofit coalition of manufacturers and window experts that has set
standards for testing and labeling windows.
NFRC currently certifies whole window U-factor, solar heat gain
coefficient (SHGC), and visible transmittance (VT). Air leakage will be added soon. Any or
all of these may appear on an NFRC label on the window. If there is no label, ask the
manufacturer for the window's NFRC ratings or look in the Certified Products Directory,
which costs $15 from NFRC (Tel:301-589-NFRC). If you get the NFRC ratings for two
windows, you know that you're comparing apples to apples.
Although the NFRC certification is voluntary, most major manufacturers now certify
their products. In California, Washington, Oregon, Idaho, Minnesota, and Alaska, building
energy codes accept certification as evidence of compliance. Several county building codes
also accept NFRC certification, and more states are likely to adopt the requirement as
they update their energy codes. These codes usually apply to additions as well as new
construction.
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