What's a Window's U-Factor?

New Replacement Window
The new replacement windows varied
in size from three to four feet wide
to seven and nine feet tall.

One of the ways windows can be compared is by looking at the unit's measured energy performance. These measurements are expressed as the "R Factor" for "resistance" or "U-Factor" which is a measurement of "thermal transference."

The National Fenestration Rating Council, or NFRC, measures product energy performance and energy-related properties of doors and windows. Using these measurements, buyers can easily ascertain if the products meet local or state codes or other performance requirements such as those used by the Energy Office for Dollar and Energy Saving Loans.

The Council has established a rigorous process by which products are rated. By certifying and labeling their products, manufacturers are demonstrating their commitment to providing accurate energy and energy-related performance information which allows customers to make informed purchasing decisions.

The Council is a non-profit, public/private collaboration of manufacturers, builders, designers, specifiers, code officials, consumers utilities and regulators.

Return to the Spring 2000 Newsletter