How to Read a Window Label
Windows are accompanied by a label that show important energy-performance ratings. Here is what each rating means so you can make an informed decision when purchasing windows.
NFRC Window Label
The National Fenestration Rating Council (NFRC) is in charge of certifying windows and providing energy performance labels that help customers determine how well a window is constructed. The information supplied on the label allows for comparison between windows so consumers are able to make informed decisions about the windows they buy.
The current label lists the manufacturer, a product description, a source for additional information, and ratings for energy performance characteristics. Because the label can be confusing to some, here is a break down of what each rating means.
A measurement of how well a window prevents heat from escaping, U-Factor ratings generally range from .20 to 1.20. The lower the U-Factor, the better its insulating value and greater the window’s resistance to heat flow.
Solar Heat Gain Coefficient
The Solar Heat Gain Coefficient (SHGC) measures how well a window blocks radiant heat caused by sunlight. Indicated by a number between 0 and 1, a lower SHGC means less solar heat is transmitted into your home.
A measurement of how much visible light is allowed through the window, Visible Transmittance (VT) is expressed as a number between 0 and 1. A higher VT means more light is transmitted.
An optional rating, manufacturers may or may not include Air Leakage on a label. It indicates how much heat loss and gain occurs through cracks in the window assembly. The lower the Air Leakage rating, the less air will pass through.
Also optional, the Condensation Resistance (CR) is a measurement of the window’s ability to resist condensation forming on its interior surface. It is indicated by a number between 0 and 100, with a higher number indicating the window is better at resisting condensation.
C.E.C. Air Infiltration Standards
C.E.C. stands for the California Energy Commission, which is the state’s primary energy policy agency. Through appliance and building standards, the C.E.C. promotes energy-efficiency. If a window meets or exceeds C.E.C. Air Infiltration Standards, it means the window construction is tight enough to comply with the commission’s air leakage standards.
An acronym that stands for the Window & Door Manufacturers Association, the WDMA defines the standards of excellence in the window, door, and skylight industry. It is a trade association whose members manufacture high-performance products designed and built to meet the associations high standards. The WDMA is a provider of resources, education and professional programs to help industry businesses offer greater value to customers.
An easily recognizable way to identify products that meet the standards set forth by the Window & Door Manufacturers Association, the WDMA Hallmark Certification Program is considered a mark of excellence among architects and contractors and is accepted industry-wide.