Energy Star-certified products are trusted for their quality and energy efficiency. Here’s how it happens.
When the National Association of Realtors surveyed Americans in 2021 on what they expect to find in an energy-efficient home, the most popular answer was efficient windows – 83 percent of respondents identified ENERGY STAR-certified windows as the most obvious ingredient. The ENERGY STAR program, overseen by the U.S. Environmental Protection Agency and the Department of Energy, rates windows, computer monitors, refrigerators, and many other common products for their energy efficiency. According to the program’s calculations, people who replace old windows with ENERGY STAR-certified versions can expect their monthly electricity bill to drop by about 11 percent. How do they know? That certainty is the result of a testing system developed by our parent organization, the National Fenestration Rating Council.
The NFRC tests roughly 80 percent of the windows in the U.S. and Canada for their energy efficiency. Most of the windows you see for sale have an NFRC label affixed to them that displays the results. NFRC certification is voluntary for window manufacturers, and most choose to do so because of the chance to build trust with customers by giving them more information. To receive the ENERGY STAR certification, companies must opt for some extra steps. About 2,500 window options that make the grade.
That process begins at one of 10 laboratories across the U.S. that NFRC has accredited to perform the tests. Each lab contains a small house inside it – a structure about 12 feet wide, 12 feet deep, and 16 feet high, with its own heating and cooling systems. The interior is like a little living room inside the lab. The windows are installed in it just as they would be in a home, but with sensors around them to measure heat flow.
Technicians then blow hot and cold air in cycles for 48 hours and monitor several factors. They calculate the amount of heat that can escape the house through the window (its u-factor), and the amount of heat that can enter through it (the solar heat gain coefficient). They also measure a third efficiency factor: the amount of light that can pass through (visible transmittance). Windows must meet specific standards for each, plus one more – the amount of air that can pass through any leaks. No window provides a perfect seal. Those that don’t qualify for ENERGY STAR still get an NFRC label detailing the results.
NFRC also evaluates the inspection agencies through yearly in-plant inspections. Conducting these inspections and life cycle testing every five years for every type of window are the basis for our product certification program. For manufacturers participating in the ENERGY STAR program, EPA requires that they submit to random product testing as an added level of scrutiny.
Finally, the ENERGY STAR process requires manufacturers to provide detailed installation instructions, which are used in testing as well as by window installers.
About 80 percent of windows are efficient enough to meet ENERGY STAR requirements, but that figure will drop later this year. That’s because ENERGY STAR periodically raises its standards, and the seventh version of them takes effect in October 2023. By increasing standards the program plays a key role in making windows more efficient over time. You can read more about your fellow window shoppers’ trust in the ENERGY STAR program and what they want in a window in this blog post on window trends we wrote in September. And try the Window Ratings page of this site for a quick guide to u-factor, visible transmittance, and the other ratings that NFRC provides to consumers and to the ENERGY STAR program.