Air Leakage (AL)

Heat loss and gain occur by infiltration through cracks in the window assembly. It is indicated by an air leakage rating (AL) expressed as the equivalent cubic feet of air passing through a square foot of window area. The lower the AL, the less air will pass through cracks in the window assembly. At this time, the AL is optional among NFRC ratings. For code compliance purposes, however, air infiltration is often tested in accordance with the North American Fenestration Standard (NAFS), which produces similar results to the NFRC air leakage rating.

Select windows with an AL of 0.30 or less (units are cfm/sq ft).

Glossary | References | Software | NFRC | ENERGY STAR® | Code Info | Links