What are the AMCA damper leakage classes?

AMCA Standard 511 defines damper leakage classes based on maximum allowable leakage per square foot of damper area at specified test pressure: Class 1 (tightest) allows 4 CFM/ft² at 1 in. w.g., Class 2 allows 10 CFM/ft² at 1 in. w.g., and Class 3 allows 40 CFM/ft² at 1 in. w.g. For outdoor air intake and exhaust dampers, Class 1 leakage rating is strongly recommended because leakage through a poorly sealed damper can cause coil freezing and significant energy waste during unoccupied winter setback. ASHRAE 90.1 effectively mandates Class 1 or better (typically ≤3 CFM/ft² at 1 in. w.g. per AMCA 511) for outdoor air and relief dampers in most commercial buildings, and dampers with jamb seals and blade edge seals are standard features to achieve these ratings.