How to Order Replacement Filters for Older Rentals With Discontinued Grille Sizes

Older rentals often come with return-air grilles, filter frames or wall cabinets that no longer match current stock sizes. When that happens, the quickest way to get the right replacement is to capture the right details before ordering, rather than guessing from the old filter alone.

At Total Air Filtration, a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, we regularly help property managers, landlords and mechanical contractors identify replacement filters for legacy systems. The more complete your information is, the easier it is to match the filter to the existing opening or design a suitable custom solution.

Start with the actual opening, not just the old filter

One of the most common mistakes is measuring only the old filter’s outer frame. That can be useful, but it is not always enough, especially if the grille or cabinet has been modified over time.

Before ordering, record the following:

• •The visible grille or cabinet opening size
• •The old filter’s actual dimensions, including depth
• •The way the filter sits in the frame: front access, side access or rear access
• •Whether the filter is held by clips, a slide-in track, a hinged grille or a separate frame
• •Any labels, stampings or handwritten marks on the grille, cabinet or adjacent ductwork

If you need guidance on measuring, our how to measure an air filter page is a useful starting point.

Measure in more than one place

Older metalwork is not always square, and timber-framed or renovated openings can vary slightly from top to bottom or side to side. Measure the opening in at least two directions and note the smallest usable dimension.

It also helps to note whether the opening is unobstructed or whether there is insulation, a lip, screws, cable runs or other fittings that reduce the clear space available for the filter.

Capture the details that affect fit and airflow

A replacement filter has to do more than match the width and height. It must also fit correctly in the housing and allow the system to move air as intended.

Useful information to gather includes:

• •Filter media type if known, such as pleated panel, pad, synthetic or disposable cardboard frame
• •Frame material, including cardboard, galvanised steel, aluminium or plastic
• •Depth or thickness in millimetres
• •Direction of airflow if marked on the filter or cabinet
• •Any seal type, such as gasket, foam edge or channel seal
• •Whether the filter is installed in a return-air grille, fan coil unit, wall cabinet or ceiling plenum

If the site has a pressure gauge or manometer fitted, note the pressure drop reading at the time of inspection. That reading can help indicate whether the filter is loading up with dust, though inspection frequency should still follow the equipment manufacturer’s instructions and suit the site conditions and dust load.

Photograph the whole assembly before removing anything

Photos often solve what measurements cannot. They show how the filter is retained, how much room there is around the frame, and whether the opening has been altered since the unit was installed.

Take clear photos of:

• •The full grille or cabinet from the front
• •The filter removed from the unit
• •The inside of the frame or track where the filter sits
• •Any labels on the grille, fan coil unit or cabinet
• •Nearby access points, hinges or screws that affect removal

If possible, include a ruler or tape measure in the photo. That gives context for the measurements and helps avoid confusion when an opening is close to a standard size but not quite exact.

Know whether you need a standard, modified or custom filter

Sometimes a discontinued grille size can still be matched with a standard stock filter if the opening has enough tolerance. In other cases, the housing needs a custom-made filter to fit properly.

A custom option may be needed when:

• •The size is an uncommon legacy dimension
• •The filter must fit a narrow or shallow cabinet
• •The frame has an unusual lip, notch or return bend
• •The opening has been altered over time
• •The system uses a non-standard retaining method

If you are unsure, send the measurements and photos first rather than assuming a close match will work. Our custom air filters page explains the type of information that helps us build to an existing opening.

Check the product requirements as well as the opening size

The right replacement is not just about dimensions. It should also suit the system’s operating needs and the intended level of filtration.

Where relevant, consider whether the site previously used a coarse pre-filter, a finer panel filter or a different media type. If the equipment manufacturer or building owner has a specified grade, follow that instruction. In Australia, site requirements may also need to align with the mechanical services engineer and the building owner, especially where AS 1668.2:2024 is relevant to the ventilation system.

Remember that MERV, EN 779 and ISO 16890 ratings do not convert directly. If a legacy job sheet lists an older rating, it is better to provide the exact filter specification and existing sample rather than try to guess an equivalent.

What to send when you request a replacement

To speed up the process, send a concise package of information in one message. Include the measurements, photos and any notes about how the filter is installed.

A good request usually includes:

• •Site name and suburb
• •Unit type or room location
• •Opening size and filter depth
• •Old filter dimensions if available
• •Photos of the grille, cabinet and removed filter
• •Any markings, part numbers or old paperwork
• •Whether you need standard replacement, modified size or a custom-made filter
• •Preferred contact details for follow-up

If the system is part of a larger commercial or rental portfolio, keep the same naming format for each unit. That makes repeat ordering easier when you are managing multiple properties or stages of a renovation.

When the old filter is damaged or missing

It is still possible to order a replacement if the original filter is broken, warped or lost, but the job becomes more reliant on the opening measurements and surrounding evidence.

In that situation:

• •Measure the internal recess as accurately as possible
• •Check for wear marks that show the previous filter footprint
• •Look for spare labels, old invoices or maintenance notes
• •Compare the opening against nearby standard sizes without forcing a guess

If the frame is bent or the grille has been modified, note that in your request. A filter that fits loosely may bypass dust around the edges, while a filter that is too tight can be difficult to install and remove.

Keep a record for future maintenance visits

Once the correct replacement has been identified, save the details for the next visit. That avoids repeating the measuring process every time the filter needs attention.

A useful site record can include:

• •Exact opening size
• •Accepted replacement size
• •Filter type and frame material
• •Photos of the installed filter and housing
• •Notes on access method and clearance issues
• •Any site-specific instructions for contractors or cleaners

For properties with multiple older units, this record also helps when arranging filter servicing or commercial filter servicing visits, especially where access is awkward or the openings vary between tenancies.

We can help identify the right fit

If you are dealing with a legacy return-air cabinet, a discontinued grille size or a filter opening that no longer matches standard stock, Total Air Filtration can help supply or make the right filter for the job. Call 07 3800 3448 or request a quote, and we will work from your measurements, photos and site details to help find a practical replacement.