ENERGY STAR qualified windows are windows that meet a strict energy efficiency specification that is set by the Department of Energy (DOE). These windows have been tested and are certified by the National Fenestration Rating Council (NFRC). NFRC an independent third-party certification agency assigns specific energy efficiency measurements for ENERGY STAR qualifications. These measures are U-factor and Solar Heat Gain Coefficient (SHGC), which rate an entire window system, no just the glass.

ENERGY STAR qualifications are always based on U-factor and SHGC ratings in each of the four climate zones. In order to meet U-factor and SHGC levels, ENERGY STAR qualified windows may use:

• Two or more planes of glass
• Warm-edge spacers
• Vinyl framing materials
• Low-E coatings (microscopic coatings that help keep heat inside during the winter and outside during the summer)

None of these are mandatory; each window manufacture determines how to make their windows meet DOE standards. View the energy efficient criteria for ENERGY STAR qualified windows.