Duct Leakage Test-and-Balance

SMACNA leakage class from measured-vs-design CFM at test pressure; pass/fail against the design class.

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Formula and source

leakage_cfm = design_cfm - measured_cfm. leak_at_1inwc = leakage_cfm / sqrt(test_pressure_inwc) (orifice-flow scaling). leak_per_100ft2 = leak_at_1inwc / duct_surface_ft2 × 100. Effective class = smallest SMACNA class (3, 6, 12, 24, 48) whose limit ≥ leak_per_100ft2.

SMACNA Duct Leakage Test Manual (3rd ed.) by name. ASHRAE 90.1-2022 §6.4.4.2-2022 (Ventilation for Acceptable Indoor Air Quality). (referenced for the leakage-class system).

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