NFRC
The NFRC (National Fenestration Rating Council) is the US body that certifies window, door, and skylight performance ratings. The NFRC label on a window reports five whole-product values: U-factor, SHGC, VT, air leakage, and condensation resistance. Because NFRC values are independently tested and standardized across manufacturers, they let you compare windows directly. Code, Energy Star, and Passive House all rely on NFRC ratings for compliance.