What is the NFRC? The National Fenestration Rating Council is the governing body that provides information on how a window performs. The two most important energy ratings are U-factor and Solar Heat Gain.
U Value is the amount of heat transmitted by the window. The lower the number, the more efficient the window is in reducing winter heating cost.
Solar Heat Gain Coefficient (SHGC) measures how well a window blocks heat from the sunlight coming through the glass. The lower a window’s SHGC, the less solar heat it transmits.
The overall window performance that NFRC has completed on Vinly Kraft Windows, Double Pane eK2 Glass With Argon Gas Fill and the Super Spacer = U Value .28 and SHGC Value .28
The overall window performance that NFRC has completed on Vinly Kraft Widows, Double Pane eK366 Glass With Argon Gas Fill and the Super Spacer = U Value .28 and SHGC Value .21
To learn more about the NFRC and windows in general you should visit their website.