How To Conduct A Ductwork Air Leakage Test: A Step-By-Step Guide
Testing ductwork for air leakage is a key stage in commissioning. It confirms that the system performs as intended and meets the required standards for airflow, energy efficiency, and compliance with Building Regulations. Excessive air leakage can reduce system performance, increase running costs, and affect comfort levels or fire safety.
DW/143, published by the Building Engineering Services Association (BESA), outlines the official UK method for testing ductwork airtightness. It explains how to select the right equipment, carry out the test, and calculate leakage rates to achieve accurate, consistent results.
This guide explains each stage of the process, from preparing and setting up the test to measuring and interpreting the results in line with DW/143.
Pretest Considerations: Preparing The System
Before starting a ductwork air leakage test, ensure that the entire system is complete, sealed, and ready for pressurisation. DW/143 advises that testing should take place once all components are installed, including fittings, dampers, access panels, and supports, but before final commissioning begins.
Selecting appropriate test sections is crucial for accurate results. Each section should represent typical areas of the system and include common features such as turning vanes, flexible joints, or volume control dampers. According to DW/143, the surface area of a test section should generally range between ten and one hundred square metres.
Effective coordination with the site team is vital at this stage. The duct system must be temporarily taken out of service, and all openings, including terminals, grilles, and access points, should be securely sealed using blanking plates, end caps, or similar covers.
Essential Equipment For Accurate Testing
Accurate air leakage testing relies on using the correct, properly calibrated instruments. At a minimum, you will need:
- A fan unit that can deliver steady airflow at the required test pressure
- A pressure measuring device (manometer or digital gauge)
- An airflow measurement tool (orifice plate or calibrated hood)
DW/143 does not mandate a specific test setup but requires all instruments to be calibrated and used according to the manufacturer’s guidance. Always check for up-to-date calibration records and visible damage before testing.
A stable, well-prepared setup ensures test results reflect duct system performance, not instrument limitations.
Test Procedure: Reaching And Holding Pressure
Once sealed and setup is complete, increase airflow until the static pressure for the leakage class is reached. Maintain this pressure for at least 30 seconds.
Continuously monitor airflow and pressure. Pressure drops or fluctuations may indicate leaks, seal failure, or equipment error. Investigate issues such as audible hissing or movement in sealing tape to avoid misinterpreting results.
If the system fails, locate and address leaks, then retest. Carefully document conditions, readings, and changes.
For more on leakage classes and test pressures, see Understanding Ductwork Leakage Classes.
Calculating Leakage Rate And Evaluating Results
DW/143 uses a standard formula to calculate air leakage in litres per second per square metre of duct surface. This ensures results are comparable between systems.
To measure surface area:
- Rectangular ducts: Multiply perimeter by length (include fittings and transitions)
- Circular ducts: Multiply circumference by length
Compare the calculated leakage rate to the limit for the specified class. If exceeded, identify and seal the issues, then retest. Keep records of all data for compliance and transparency.
Avoiding Common Test Failures
Failures are often due to test setup issues rather than poor ductwork. Common errors include:
- Inadequate sealing at terminals or access doors
- Weak temporary caps or blanking plates
- Uncalibrated instruments
- Environmental interference (draughts, other systems)
Plan ahead. Ensure the area is isolated, the system is complete, and all seals meet DW144 requirements. Coordinate with site teams to keep the testing zone undisturbed.
Verify Airtightness With Confidence
A successful leakage test confirms the system meets project, regulatory, and performance targets. It ensures efficient airflow and minimises energy waste.
DW/143 provides a reliable method to test and verify duct airtightness. Following its guidance improves accuracy and builds trust with clients.
Download DW/143 today from the BESA Publications website to ensure your testing process is compliant, consistent, and verifiable.