Rating Only the Center of Glass has Drawbacks

Glazed framing systems have improved over the years and left metal-framed, single-paned windows obsolete.

Dual glazed insulating units, low-emissivity coating, and thermally improve frames now provide significant energy savings.

Industry professionals didn’t pay much attention to the energy performance of glazed framing systems until recently. For many years, most of the U.S. was satisfied with using the Center of Glass U-factor for determining the energy-performance calculations of buildings.

The framing around the glazing, however, can be one of the biggest contributors to a system’s energy performance. An insulating glazing unit with a U-value of 0.29 glazed into a poorly performing framing system can result in an overall U-value of 0.60.

Therefore, an energy calculation done for a building using only the Center of Glass U-factor does not produce an honest or realistic result.

This is where the National Fenestration Rating Council (NFRC) comes in.

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