Air leakage is an important consideration when designing, manufacturing and installing commercial ductwork. Excessive leakage can reduce system performance, increase energy use and make a ventilation system more difficult to balance.
DW/144 provides recognised guidance for the construction of sheet metal ductwork used in heating, ventilation and air conditioning systems across the UK.
What is ductwork air leakage?
Ductwork air leakage occurs when air escapes through joints, seams, access panels, connections or poorly sealed sections of a ventilation system.
In extract systems, unwanted air may also be drawn into the ductwork through gaps and weak points. Both situations can affect the amount of air reaching its intended destination.
Why does air leakage matter?
A ventilation system is designed to move a calculated volume of air around a building. When air escapes from the ductwork, the system may no longer deliver the required airflow.
Excessive air leakage can contribute to:
- Reduced airflow at grilles and diffusers
- Higher fan energy consumption
- Difficulty balancing the ventilation system
- Increased operating costs
- Noise around poorly sealed joints
- Reduced overall system efficiency
How DW/144 relates to air leakage
DW/144 sets out construction requirements for sheet metal ductwork, including jointing, reinforcement, sealing and pressure classifications.
The required construction method depends on factors including duct dimensions, operating pressure, material selection and the intended application.
For a broader introduction to the standard, read our complete guide to the DW/144 standard.
Pressure classes and leakage
Air leakage becomes more important as the operating pressure of a system increases. Higher internal pressure places greater force on seams, joints and duct surfaces.
Higher pressure systems may therefore require stronger joints, additional reinforcement and more extensive sealing than lower pressure systems.
Our guide to DW/144 pressure classes explains how operating pressure affects ductwork construction.
Common causes of ductwork leakage
Air leakage is often caused by problems at connection points rather than through the main duct surface.
Common causes include:
- Poorly assembled flanges
- Loose or missing fixings
- Damaged seals and gaskets
- Unsealed corners
- Incorrectly fitted access panels
- Poor connections between ductwork and equipment
- Damage caused during transport or installation
The importance of correctly sealed joints
Ductwork joints must be assembled and sealed correctly to maintain the intended system performance.
The appropriate sealing method depends on the joint design, pressure classification and project specification. Sealants, tapes and gaskets must also be suitable for the operating environment.
Does all ductwork require leakage testing?
Air leakage testing may be required by the project specification, consultant or commissioning engineer.
Testing normally involves temporarily sealing sections of ductwork and applying a controlled pressure. The measured leakage is then compared with the permitted level for the system.
The exact testing requirements should be confirmed before manufacture and installation begin.
Manufacturing quality and air leakage
Accurate manufacturing makes it easier to assemble and seal ductwork correctly on site.
Consistent dimensions, properly formed joints and correctly fitted components reduce the likelihood of gaps appearing during installation.
Manufacturing quality is particularly important for larger ducts and higher pressure systems where movement and flexing can place additional stress on joints.
Installation and commissioning
Even correctly manufactured ductwork can leak if it is damaged or assembled poorly during installation.
Installers should inspect joints, access panels, flexible connections and equipment connections before the system is commissioned.
Any visible gaps or damaged seals should be corrected before airflow balancing or leakage testing takes place.
Reducing air leakage in commercial ductwork
Air leakage can be reduced through careful specification, accurate manufacture and proper installation.
Important steps include:
- Confirming the correct pressure class
- Using suitable jointing and sealing methods
- Following the project specification
- Protecting ductwork during transport
- Checking joints during installation
- Testing where required
Conclusion
Controlling air leakage is essential for efficient and reliable commercial ventilation systems. Correctly manufactured and installed DW/144 ductwork helps maintain airflow, reduce wasted energy and support successful system commissioning.
The required leakage performance and testing arrangements should always be confirmed with the system designer before ductwork manufacture begins.