How does an Energy Star window differ from other windows?
Energy Star labeled windows meet a stringent energy efficiency specification set by the U.S. Department of Energy, and have been tested and certified by the National Fenestration Rating Council (NFRC). NFRC is an independent, third-party certification agency that assigns specific energy efficiency measures such as U-factor and Solar Heat Gain Coefficient to the complete window system, not simply the glass. Energy Star qualified windows may have two or more panes of glass, warm-edge spacers between the window panes, improved framing materials, and Low-E coating(s) which are microscopically thin coatings that helps keep heat inside during the winter and outside during the summer.
