NFRC stands for National Fenestration Rating Council.
The NFRC is an independent non profit organization which tests and certifies windows to certain performance ratings to help consumers compare the performance of one window with the performance of another window.
The windows are tested using computer simulation and physical testing at laboratories accredited by the NFRC.
The U-factor measures the rate at which heat transfers and is an indicator of how well a window insulates so the lower the U-Factor the better the window insulates. According to Energy Star U-factor values generally range from 0.25 to 1.25.
The Solar Heat Gain Coefficient
The Solar Heat Gain Coefficient (SHGC) measures the solar energy that is transmitted through the window. This measurement is scaled from 0 to 1 and is an indicator of how well the window blocks heat that is caused by sunlight. Again, the lower the number the less solar heat is transferred through the window. According to Energy Star the SHGC values typically range from 0.25 to 0.80.
The Visible Transmittance
The Visible Transmittance rating’s range is from 0 to 1 and measures the light that is permitted through the window. The higher the Visible Transmittance value the better the window allows light to pass through it. According to Energy Star, values generally range from 0.20 to 0.80.
DP or Design Pressure
DP or Design Pressure rating which tests the ability of the window to survive a certain amount of positive or negative pressure per square foot.
The DP rating required for different applications varies based on many factors which will be outlined in the local building code. The higher the DP rating the better the window will stand up to design pressure criteria.