Measuring a Window’s Energy Efficiency

How Do You Measure a Window’s Performance?

Industry standards have been established.

What is the NFRC?

The National Fenestration Research Council (NFRC) is an independent, non-profit organization that administers the only nationally accepted rating system for energy performance of windows, doors and skylights. The NFRC provides fair, accurate and reliable energy performance ratings so that architects, engineers, builders, code officials, contractors and homeowners can compare different products and make informed choices.

U-Factor

The most important measure of a window’s performance is its U-Factor. The U-Factor indicates the rate of heat flow through a window. The lower the U-Factor, the more energy efficient the window will be. U-Factor measures the entire window unit — glass, frame, sash, spacers — and is the only measurement accepted by the U.S. Department of Energy’s EnergyStar program.

R-Value

R-Value is the measure of the independent parts of the window; for example, the glass, sash, frame, etc. Althouigh this is important, don’t be fooled by high R-Value statements. Some products have high R-Value, but also a high U-Factor, and its overall energy performance is poor. The NFRC, or Energy Star only recognizes U-Factor as the overall measure of how a window performs on energy-efficiency measures.

Look for the NFRC label on any window you purchase.

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