What is duct leakage testing?

Pressurizing a sealed duct section with a calibrated fan and measuring how much air leaks out (CFM) to verify the ductwork meets the specified leakage class.

When is duct leakage testing required?

When required by energy code (ASHRAE 90.1 / IECC), by the specification, or by the commissioning agent. Many jurisdictions require it on medium- and high-pressure ducts.

What is an acceptable leakage rate?

Depends on duct pressure class. ASHRAE 90.1 and SMACNA define leakage classes (e.g., Class 6, Class 12) with maximum allowable CFM per 100 sq ft of duct surface.

Duct Leakage Testing (DALT) — SMACNA Standards

Duct leakage testing (DALT) quantifies how much conditioned air is leaking from a ductwork system into unconditioned space. We perform DALT under the SMACNA leakage class standards using a calibrated test fan, digital manometer, and inflatable test plugs.

Duct leakage testing — commercial supply duct labeled SUPPLY at ceiling, the kind of seam tested under SMACNA Class A/B/C — Commercial sheet metal supply duct — typical SMACNA leakage test target.

When duct leakage testing is required

IECC and ASHRAE 90.1 require duct leakage testing on most new commercial construction. Utility rebate programs and LEED submittals reference the same standard. Retrofit duct work and any major mechanical renovation typically require pre- and post-installation testing.

Our duct leakage testing field procedure

Section plan developed from mechanical drawings — pressurized and non-pressurized runs identified
Test fan calibrated and zeroed before each section
Each section pressurized to design pressure (typically 1.0 to 6.0 in.wg)
Measured leakage flow logged against the SMACNA leakage class limit
Leaking joints, seams, and fittings photographed for the corrective punch list

Duct leakage testing deliverable

Stamped DALT report with measured leakage rates per section, SMACNA class comparison, photo documentation of every deficiency, repair locations marked on drawings, and calibration certificates for the test fan and manometer.