Allowable Leakage based on SMACNA Leakage Class

SMACNA and NEBB recommend use of leakage class for specifying allowable leakage. To calculate allowable leakage, you must know the system surface area, the required test pressure and the specified leakage class.

System (or section) Surface Area:
Test Pressure:
SMACNA Leakage Class*:
Allowable leakage based on your input is:
Calculate Leakage Allowed

*SMACNA recommends using leakage classes in table below when the designer has not designated leakage limits. Please refer to the SMACNA HVAC Air Duct Leakage Manual published by Sheet Metal and Air Conditioning Contractors National Association, Inc. (SMACNA).
Duct Class 4, 6, 10 in.wg. 3 in.wg. 1/2, 1, 2 in.wg.
Seal Class A B C
What gets sealed? Joints, seams, wall penetrations Transverse joints and seams Transverse joints
Metal Rectangular Duct Leakage Class = 4 Leakage Class = 8 Leakage Class = 16
Metal Round Duct Leakage Class = 2 Leakage Class = 4 Leakage Class = 8
We assume no liability for use of this program. We have made every effort available to make sure this program calculates correctly. Calculation of allowable leakage using leakage class is derived from SMACNA HVAC Air Duct Leakage Test Manual - 2nd Edition.