How to Tell if a Damaged Filter Frame Is Causing Odour Leakage

If you can still smell the source of an air stream after a filter has been installed, the media may not be the problem at all. In many HVAC and exhaust-related systems, odour can slip around a damaged frame, split corner or warped cardboard edge instead of passing through the filter media. That makes a careful visual check just as important as checking the filter rating.

Why the frame matters as much as the media

A filter works properly only when air is forced through the media and not around it. The frame is what keeps the filter square, sealed and sitting correctly in the holding frame or track.

When the frame is sound, it helps maintain contact with the filter housing and prevents bypass. When it is damaged, air can take the easier path through gaps, cracks or lifted edges. That is especially important where odours are present, because even a small opening can let untreated air through.

This can happen in a range of installations, including:

• •home return air systems
• •kitchen exhaust pre-filtration
• •workshop extraction and general exhaust units
• •commercial HVAC plant with panel or bag filters
• •site-specific systems designed under AS 1668.2:2024, where the mechanical services engineer or building owner should confirm requirements

If you are unsure whether the issue is filter-related or system-related, it can help to compare the installed unit with the original specification. Our how to measure an air filter guide can help if you need to confirm the dimensions before ordering a replacement.

Common frame faults that allow odour leakage

Cracked frames

A crack in a plastic, metal or cardboard frame can create a direct path for air to bypass the media. Even if the crack looks small, it can open further under pressure, vibration or handling.

Look for:

• •visible splits along the frame edge
• •hairline cracks at stress points
• •gaps that widen when the filter is flexed lightly
• •stains or dust tracks that suggest air has been escaping around the frame

Split corners

Corners are a frequent failure point because they take the load when a filter is inserted, removed or handled roughly. A split corner can lift the seal at one end of the filter and leave a gap between the frame and the housing.

Check for:

• •corners that no longer sit flush
• •open mitres or separation at glued joints
• •tape repairs that only cover part of the damage
• •evidence of odour leakage strongest near one corner of the frame

Warped cardboard

Cardboard-framed filters can warp if they have absorbed moisture, been stored poorly or been exposed to heat and humidity. A warped frame can twist the filter out of square and prevent an even seal.

That uneven fit can allow air to bypass the media along one side, especially in systems with strong airflow or vibration.

Signs of warping include:

• •bowed sides
• •corners that no longer align with the filter housing
• •frayed or softened edges
• •the filter rocking or sitting unevenly in the frame

How to inspect for bypass and leakage

Start with the filter removed, if the system can be safely shut down and isolated. Then inspect both the filter and the filter seat. You are looking for anything that would stop the frame sealing flat and square.

What to check on the filter itself

• •cracked or broken frame material
• •torn media near the edge where it meets the frame
• •loose seals or gasket material
• •bent wire supports, where fitted
• •collapsed corners or distorted end caps

What to check in the holding frame or housing

• •buildup of dust or grease on the seating surface
• •bent tracks, rails or clips
• •damaged gaskets or missing seal strips
• •signs that the filter has been forced in at an angle
• •gaps between the filter edge and the housing when installed

A simple clue is dust patterning. If the filter media is relatively clean in one area but there is dust or odour residue along the frame edge, air may be moving around the filter rather than through it.

When the filter itself is not the only issue

A damaged frame may be the obvious fault, but the housing or installation can also contribute to odour leakage. If the filter is the wrong size, even by a small margin, it may not seal properly. If the holding frame is bent or the access door is not closing evenly, air can escape through the same gap every time a new filter is installed.

This is why matching the filter to the actual opening matters. If you need a replacement, confirm the dimensions carefully before ordering. For non-standard sizes or unusual housings, custom air filters can be made to suit the application.

Other things to consider:

• •vibration from fans or nearby equipment can loosen a marginal seal
• •humidity can soften cardboard and distort frames
• •poor handling during change-out can bend a frame before installation
• •repeated re-use of a damaged filter can make leakage worse

Some filters are designed to be washable - check the product instructions. If a washable product has been damaged, warped or split, washing will not restore the frame to its original shape.

Choosing the right replacement to stop bypass

If odour control is part of the job, the replacement filter needs the right media, frame and fit. In some systems that may mean a deeper panel, a pleated filter, a bag filter or another style from our products. The correct choice depends on the system design, airflow, contaminant type and available space.

A replacement should be selected with the following in mind:

• •the filter must fit the opening without forcing
• •the frame should remain rigid enough for the operating conditions
• •the sealing surface should match the housing design
• •the media must be appropriate for the application, whether that is general HVAC or exhaust-related use
• •the system should still be checked after installation for pressure drop where gauges are fitted

If you are maintaining a larger site, it may also help to arrange ongoing filter servicing or, for larger commercial systems, commercial filter servicing. Inspection frequency depends on the system, site conditions and dust load, and it should follow the filter and equipment manufacturer instructions.

Signs it is time to replace the filter rather than repair it

Some frame damage can be obvious enough that repair is not worthwhile. A taped corner or bent edge may hold temporarily, but it can still leak. If the filter no longer sits square, or if the frame has lost its rigidity, replacement is usually the safer and more reliable option.

Replace the filter when you see:

• •cracks that run through the frame body
• •split corners that cannot be resealed neatly
• •cardboard that has warped, softened or delaminated
• •a persistent odour even after the filter has been reseated
• •repeated leakage from the same location after cleaning the housing

If you are managing filters for a warehouse, office, workshop or mixed-use building, it can also help to review the broader system and not just the visible panel. Site-specific ventilation requirements should be confirmed with the mechanical services engineer or building owner, particularly where AS 1668.2:2024 is being used as the reference point.

Get the right fit for a better seal

A damaged frame can undermine even a good filter if the air can go around it. The quickest way to narrow down the cause is to inspect the frame, the corners and the housing together, then replace any filter that no longer seals properly.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, and we can supply or make the right filters for your application. Call 07 3800 3448 or request a quote. You can also contact us if you need help confirming the right size or style.