NFRC TESTING

The National Fenestration Rating Council is an non-profit, independent organization, who provides uniform, accurate information about the energy performance of windows, doors and skylights. The NFRC label shown is applied to the window at the manufacturing plant, and lists the ratings of the window in four areas:

Air Leakage

Measures how much outside air infiltrates into a home through the window. The lower the Air Leakage (AL) rating, the better a product is at keeping outside air out - both cold air in the winter and hot air in the summer. Air Leakage rates generally fall between .1 and .4, however, there are a few high performance windows with AL ratings as low as .02.

U-Factor

Measures how well a window prevents heat from escaping a building. U-Factors generally fall between .20 and 1.20. The lower the U-Factor, the better. U-Factor is particularly important in northern climates, however it can be a good indicator of how well a window performs overall. U-Factor is the opposite of the R-Factor, so where R-Factor measures resistance to heat loss, U-Factor measures the amount of heat loss. A brand new single pane aluminum window will generally have a U-Value of 1.1.

SHGC

Measures how well a product blocks heat caused by the sun. SHGC is expressed as a number between 0 and 1. A lower SHGC means less heat gain. A simple way to explain SHGC is in terms of a ratio; where 1 is the maximum amount of solar heat gain that can come through a window and 0 is the least amount. A SHGC of .30 then means that 30% of the available solar heat is coming through the window. SHGC is particularly important in southern climates. A single pane aluminum window will generally have a SHGC of .85.

Visible Transmittance

Measures how much light comes through a product. VT is expressed as a number between 0 and 1. The higher the VT, the more light a window allows to penetrate. As a general rule, the better the SHGC, the lower the VT. In choosing the right window for your home, you should find a compromise between SHGC and VT which best suits your particular needs.