WINDOWS SINCE 1995

Understanding The Performance Ratings Of Windows Before You Buy

The National Fenestration Rating Council (NFRC) operates a volentary program that test and certifies labels for skylights, doors and windows. The NFRC label provides relevant information based on several performance characteristics:

(1) U-Factor of the entire window - the lower the U-factor, the more energy efficient the window.

(2) Solar Heat Gain Coefficient (SHGC) - A window with a high SHGC is better for solar heat gain and a window with a low SHGC is more effective at reducing cooling loads during the summer by blocking heat gains.

(3) Air Leakage - Expresses in cubic feet per minute per square foot of the frame. A low air infiltration window means a tighter frame.

(4) Visible Transmittance (VT) – a higher VT number window transmits more visible light. The VT of a window you select should be based on the rooms daylighting requirements.

(5) Light-To-Solar Gain (LSG) - the ratio between SHG and VT and tells us how efficient a window is when it comes to allowing light in while limiting excessive heat gains.

(6) ENERGY STAR - The NFRC label can be found on all ENERGY STAR rated windows, doors and skylights. ENERGY STAR is qualification only for minimum requirements based on U-Factor and SHGC ratings only.

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