The rating system for replacement windows for consumers we run by the National Fenestration Rating Council. Key rating information to consider is Air Leakage, Solar Heat Gain Coefficient, U-Factor,and Visible Transmittance. Their official website is http://www.nfrc.org/. They are a non profit organization whose goal is to provide fair, accurate, and reliable energy performance ratings. They were
. originally formed in response to the energy crisis of the 1970's.
