NFRC rates window and door energy efficiency
With more and more homeowners striving for energy efficiency, many homeowners are considering replacement windows. To take advantage of the return of a federal tax credit, new windows for existing homes must be ENERGY STAR-qualified.
Behind the scenes of the ENERGY STAR rating that you'd find on windows is the work of the National Fenestration Rating Council. The NFRC provides third-party energy ratings of windows, doors and skylights that can help consumers make informed purchasing decisions.
You’ve probably seen NFRC’s energy performance labels on windows or doors at home improvement stores and dealer showrooms. These labels are similar to the MPG stickers on new cars – they allow consumers to compare product performance.
NFRC is a non-profit organization, and the nationally recognized leader in energy rating and certification programs for windows, doors, skylights and other fenestration products. Its ratings are a prerequisite for participation in the ENERGY STAR Windows Program.
When you're in a home supply store or discussing windows with your contractor, here a few things to keep in mind when you're looking at the ENERGY STAR label
There are a several entries on the labels, but there are two that are most meaningful for energy performance, according to Tom Herron, senior communications and marketing manager for the NFRC.
U-factor is a measure of heat loss. "The lower the U-factor, the greater the window resists heat flow," Herrons said. "If you're running the heat in the house and a lot of it is going out the window, then they're not very efficient."
Solar Heat Gain Co-efficient is a measure of how much solar radiation is emitted through the window.
"The lower the number of the solar heat gain co-efficient, the less solar heat is transmitting into the house," Herron said. "That means there's less heat escaping in the winter and in the summer there's less heat from the sun entering your house so you don't have to run the air conditioning as much."
For both numbers, the lower the number the better the window's performance, Herron said.
The other common number is the visible transmittance, which measures the amount of visible light that's transmitted through the window.
"The idea there is if there's good visible light you don't have to run interior lighting as much and that contributes to energy efficiency."
Herron also noted that the NFRC rates the entire window unit, not just the glass itself. That includes the frame, glass and window spacers.
Windows today are much more energy efficient than in years gone by, where single panes of glass in aluminum frames were common in many homes.
Today, manufacturers offer dual pane and quadruple pane of gas, inert gases such as krypton or argon that fill the spaces between the panes and insulated frames that all contribute to better performance.
"They have come along way over the years and they're always getting better," Herron said.
Read more about energy-efficienct windows and doors.