Air leakage
AL — air leakage · the draft number
An NFRC rating for how much air slips through the window assembly. Lower means fewer drafts; on the label it's reported as 0.3 or lower.
What it means for you
The number behind the #1 complaint — “I feel a draft with the window shut.” Compression-seal styles (casement, awning) score best; sliders and hung windows a bit worse. But a great rating still needs a good install to matter.
Where you'll see it
An optional box on the NFRC label; lower is better.
Related terms
Defined by Marc Hanley
Verified against NFRC
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