Why a Newbuild Site Keeps Blowing Filters Out During Commissioning

Commissioning is when a new HVAC system is pushed through its first real tests, and that is often when filter problems show up. If filters are being dislodged, sucked into the plenum or damaged before handover, the issue is usually not the filter alone. It is more often a mix of fan setup, pressure changes, installation details and temporary site conditions that were not part of the final operating state.

For builders and commissioning contractors, this is worth tackling early. A filter that is correctly selected for the application can still fail to stay in place if the frame, holding arrangement or airflow conditions are wrong during startup. At Total Air Filtration, a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, we regularly help sites work through these practical problems and match the filter to the system that is actually on site.

Why filters come loose during commissioning

The commissioning phase is different from normal operation. Fans may be run at varying speeds, dampers may not yet be fully set, and parts of the system may be isolated, opened or adjusted while other areas are being tested. Those temporary conditions can create air velocities and pressure differences that the final design never intended the filter to see.

Common reasons filters are blown out or displaced include:

• •Fans starting up before all restraints, clips or retaining parts are installed
• •Incorrect fan rotation, fan speed or control settings creating higher-than-expected airflow
• •Temporary pressure changes when dampers are closed, opened or rebalanced
• •Filters fitted into frames that are loose, distorted or not properly seated
• •Missing gaskets, seals or edge supports that allow bypass and movement
• •Incomplete construction dust control, where debris interferes with seating surfaces
• •Filters installed before the final access doors, supports or retainers are in place

A filter may appear secure when the system is off, then shift as soon as a fan ramps up or a zone is isolated. If there is a path for air to pull against the filter edge, the filter can flex, rattle or be drawn out of position.

Check the fan setup before blaming the filter

One of the first things to review is the fan setup. During commissioning, fans are often tested, adjusted and re-tested, and those changes can alter the pressure acting on the filter bank.

Points to confirm

• •Fan rotation matches the intended direction
• •Variable speed drives are set correctly for the test stage
• •Dampers are positioned as planned for the current test condition
• •Filters are installed only after the supporting frame is ready and aligned
• •Access doors and panels are secure before the system is started
• •Any temporary bypass arrangements are removed when no longer required

It is also important to remember that a system can behave differently when only part of the building is online. Pressure changes in one zone can affect another zone, particularly in larger commercial and industrial projects. If a filter bank is exposed to a stronger-than-expected pressure differential, the filter media may not be the issue; the frame or restraint detail may be.

If you are still selecting products for a staged handover, our products page is a useful starting point, and custom sizes or configurations may be available through custom air filters.

Temporary pressure changes can dislodge a correctly fitted filter

Commissioning often involves short periods of unusual pressure. These can happen when the system is intentionally operated outside its final settings to test controls, balance airflow or verify alarms and interlocks. In that environment, filters may move even if they were fitted properly for normal service.

Examples of temporary pressure conditions include:

• •Doors or access panels being opened while fans are running
• •Air handling units operating before all branches are connected
• •Control sequences changing rapidly during testing
• •Return air and supply air paths being altered between test runs
• •Construction staging that leaves parts of the system temporarily unbalanced

This is where site coordination matters. The mechanical services engineer, commissioning contractor and builder should confirm the intended test sequence so that filter banks are not exposed to conditions they were never meant to handle. For reference, site requirements should be checked against AS 1668.2:2024 and the mechanical services engineer or building owner’s requirements.

If the system includes pressure monitoring, watch the pressure drop where gauges are fitted. That does not just help with performance checks later on; it can also show when airflow conditions are outside what the filter arrangement is likely to tolerate.

Missing restraints, poor frames and other installation faults

A lot of blown-out filter issues are really restraint issues. The filter itself may be serviceable, but the frame, clips, holding bar or sealing arrangement is not doing its job.

Look closely at the following

• •Hold-down clips or retaining bars that were never installed
• •Clips fitted loosely or with the wrong orientation
• •Frame lips that are bent or not square
• •Gasket material that is missing, compressed or damaged
• •Filter dimensions that do not match the installed opening
• •Panels or access hardware that interfere with proper seating

Even a small mismatch can matter. If the filter is undersized for the frame, air can leak around the edges and create flutter. If it is oversized or forced into place, it may deform and lose stability when airflow starts. If you need help checking dimensions before ordering replacements, see how to measure an air filter.

Some filters are designed to be washable, but that is a property of specific products only. Always check the product instructions before cleaning or reusing anything. For most sites, the safer approach is to verify that the filter type, frame and restraint method are all suitable for the actual operating conditions.

How to reduce repeat failures during handover

The best way to stop repeat blow-outs is to treat filter retention as part of commissioning, not as an afterthought. That means checking the installation details while the system is still accessible and before final sign-off.

A practical approach is to:

• •Confirm the filter size and orientation against the installed opening
• •Inspect the frame for damage, distortion or debris
• •Verify that all hold-down parts are present and tightened correctly
• •Start fans gradually and observe the filter bank during the first run
• •Recheck seals and seating after each major airflow adjustment
• •Keep spare filters on hand in case a unit is damaged during testing

If the system is serving a commercial or industrial site, it may also be worth arranging ongoing support once handover is complete. Our filter servicing and commercial filter servicing pages outline how we support filter supply and maintenance across different sites.

The key point is simple: if a filter is being blown out during commissioning, do not assume it is a product fault. Look at airflow, pressure, frame alignment and restraint hardware together. That is usually where the real problem sits.

Getting the right filter and support before handover

If you are dealing with repeat filter movement on a newbuild site, Total Air Filtration can help supply or make the right filters for the system and the stage of the project. We work with builders, commissioning contractors and other commercial sites from our Brisbane base, and we can help with standard and custom requirements.

For assistance, call 07 3800 3448 or request a quote. You can also contact us if you need help matching a filter to the system conditions on site.