Fenestration: Product Ratings

Understanding NFRC Energy Performance Labels

by Kat Wiseman, WDMA PR Committee member

The National Fenestration Rating Council (NFRC) was founded in 1989 to create a uniform method for the energy performance ratings of window, door, and skylight products.  In 1992, Congress codified NFRC’s role as the nation’s organization for rating the energy performance for fenestration products in the National Energy Policy Act, and NFRC is the leader for ensuring fair and accurate energy ratings of these products.

         The United States building sector, which consists of more than 85 million existing residential and commercial buildings, accounts for approximately 40% of the United States’ primary energy consumption and 39% of United States carbon dioxide emissions.  According to the Department of Energy, heat gain and heat loss through windows of existing homes are responsible for 25-35% of residential heating and cooling energy use.  Using higher-performing products for new construction, and replacing clear glazed windows during remodeling, offer significant opportunities for building energy savings.

         Several factors account for the energy performance of fenestration products.  The NFRC addresses the ratings for the energy flow through products and rates the heat transfer and solar heat gain, as well as visible light transmittance and air infiltration.  The most apparent property for the thermodynamics of a system is the temperature-driven heat transfer from a higher temperature to a lower temperature, measured as a U-Factor.  The U-Factor rating is very important, as it quantifies how a product prevents heat from transferring from a warm surface to a cold surface.  The lower the U-Factor, the better a product is at keeping heat inside the building.  NFRC U-Factor ratings are based on winter nighttime conditions of exterior 0º F and interior 70º F.  This NFRC label displays U-Factor in United States units.  Labels on products sold in markets outside the United States may display U-Factors in metric units.

         The solar heat-gain coefficient is the measure of heat gained through fenestration products by direct or indirect solar radiation.  The higher the number, the higher the solar heat gains.  Visible transmittance is a measurement of the amount of light that transmits through the product.  This is a benefit to effectively light a home or work space with daylighting, potentially reducing the demand for artificial lighting.  The higher the visible transmittance number, the more natural light transmits through the product.

         The NFRC label clearly identifies the NFRC as the certifying agency, as well as the manufacturer and product description.  The required code information is also included for the U-Factor, solar heat-gain coefficient, visible light transmission, and air infiltration.  Note that air infiltration is an optional rating for the NFRC, but is a requirement of the building code, as well as for compliance with the NAFS standard.

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