Duct Leakage Test-and-Balance
SMACNA leakage class from measured-vs-design CFM at test pressure; pass/fail against the design class.
Example
You enter
- Design CFM 1000
- Measured CFM at registers 60
- Duct surface area (ft²) 300
- Test pressure (in WC) 1
You get
- Leak at 1inwc 940
- Leak per 100ft2 313.33
- Target class 6
- Target label Class 6 - sealed metal duct
- Pass No
Details, formula, and sources
leakage_cfm = design_cfm - measured_cfm. leak_at_1inwc = leakage_cfm / (test_pressure_inwc)^0.65 (SMACNA leakage-class flow exponent). 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).
SMACNA standards licensed; class-system overview free at smacna.org outreach. Free read-only access to ASHRAE standards at ashrae.org (Technical Resources, read-only standards).
Estimate. AHJ and licensed mechanical contractor govern. ACCA Manual J / D / S supersede rules of thumb.
Field names used by the API: design_cfm, measured_cfm, duct_surface_ft2, test_pressure_inwc, leak_at_1inwc, leak_per_100ft2, target_class, target_label, pass
- Leakage scales with P^0.65 SMACNA leakage-class flow exponentSMACNA Duct Leakage Test Manual
- Leakage classes 3 / 6 / 12 / 24 / 48 cfm per 100 ft² at 1 in WCSMACNA Duct Leakage Test Manual