Duct leakage testing to SMACNA
Duct leakage testing means sealing the section of duct to be tested, pressurising it with a test fan to a set pressure, and measuring the air that leaks out against the allowable leakage for the leakage class in the design. The standard method is the SMACNA HVAC Air Duct Leakage Test Manual.
Key facts
Standard
SMACNA HVAC Air Duct Leakage Test Manual
When to test
During installation (before ceilings are closed or insulation is applied) and before handover
Deliverables
A report for each duct section: duct surface area, test pressure, measured leakage, allowable leakage and pass/fail
Why test
- Air leaking from ducts means less air reaches the rooms than designed, affecting cleanroom pressure and air change rates.
- AHU fans must work harder to make up for the leakage, using more energy.
- Return ducts or ducts under negative pressure may draw unfiltered air into the system.
- Leaks are easiest to repair before ceilings are closed, so testing during installation reduces rework later.
Photos from real sites
Duct leakage testing on site
Test procedure
1
Isolate the section: seal duct ends, diffusers and openings in the section to be tested
2
Connect the test rig: connect the test fan and calibrated measuring equipment
3
Pressurise: pressurise or depressurise to the test pressure for the duct pressure class
4
Measure leakage: record the flow needed to hold the pressure
5
Compare and report: compare with the allowable leakage for the leakage class and conclude
Frequently asked questions
What is a leakage class?
The value set by the designer for the maximum allowable leakage per duct surface area at a given test pressure. The lower the value, the tighter the duct must be.
At what stage of the project should we test?
During installation, before ceilings are closed or insulation is applied, while leaks are still easy to reach and repair.
Do we test all ductwork or only part of it?
It depends on the contract and design requirements. Some projects specify a percentage of duct length, others require all ductwork to be tested.
What happens if a section fails?
The contractor seals the leaks and the section is retested until it passes.
Request a quote
Tell us the project size, the duct length or surface area, and the leakage class specified in the design
