Custom Filters for Older Buildings and Hard-to-Source Equipment

Older buildings often hide a practical problem behind otherwise familiar plant rooms: the air filter that fits properly is no longer easy to find. Heritage properties, ageing commercial sites and discontinued equipment can all end up relying on made-to-order filters to keep air handling systems operating as intended.

For facility managers and contractors, the challenge is usually not just finding a filter in the right dimensions. It is making sure the replacement suits the frame, the airflow path, the dust load and the original equipment design without forcing awkward modifications that create more work later.

Why older buildings need a different filter strategy

Buildings age in different ways. Ductwork may have been altered, fan systems may have been upgraded in stages, and original equipment manuals may be missing. In some sites, the filter arrangement in use today is not the same as the one first installed.

That matters because standard off-the-shelf filters are designed around common sizes and common applications. In older sites, you may encounter:

• •non-standard face dimensions
• •shallow filter boxes with limited clearance
• •unusual flange or frame details
• •obsolete holding frames or clip systems
• •equipment where access is tight and removal is awkward

When a standard filter does not fit correctly, it can allow bypass around the edges, reduce effective dust capture, or make maintenance unnecessarily difficult. A custom filter can be built to match the available space and the existing housing, which helps the system operate as designed.

Common situations where made-to-order filters make sense

Custom filters are often needed when the equipment itself is no longer current, but still has to keep working. That can apply to older offices, schools, hospitals, retail centres, warehouses and industrial sites, as well as heritage-listed buildings with limited room for modifications.

Discontinued or unusual equipment

Some air handling units, fan coil systems and packaged plant rooms use dimensions or retaining methods that are no longer standard. Replacement filters may need to match:

• •uncommon nominal sizes
• •proprietary frame depths
• •side access or front access housings
• •rigid frames or special seals

If the original equipment has been replaced piecemeal over time, the filter section may be a mix of old and new components. In that case, a made-to-order approach can be the simplest way to restore a proper fit.

Heritage and architecturally sensitive sites

In heritage buildings, the priority is often to maintain function without altering the building fabric more than necessary. That can limit the options for replacing filter housings, enlarging access doors or changing ductwork.

Custom filters can be useful where the original opening must be retained, or where the filter needs to be made to suit a frame that cannot be altered without affecting the building or the equipment around it.

Sites with mixed maintenance history

Ageing commercial properties often have a long maintenance history, with changes made by different contractors over time. If drawings are incomplete, the measured opening may not match what was expected from the original documentation.

In those cases, it is worth checking the filter size on site rather than assuming the old part number is still correct. If you need guidance on measuring, see how to measure an air filter.

What to check before ordering a replacement

A good custom filter starts with accurate site information. Before placing an order, it helps to confirm the following:

• •exact filter width, height and depth
• •whether the size is the opening size, the frame size or the media size
• •the type of frame required
• •the direction of airflow through the system
• •the available clearance for removal and installation
• •the dust conditions at the site
• •whether the filter is mounted in a rigid frame, slide track or bag arrangement

If the system uses a non-standard arrangement, photos can be useful as well as measurements. A clear image of the existing filter, its sealing edge and the housing can save time and reduce the risk of ordering the wrong item.

Where the site is part of a regulated ventilation design, confirm requirements with the mechanical services engineer or building owner. If AS 1668.2:2024 is relevant to the installation, the site requirements should be checked against the applicable design and maintenance expectations rather than assumed.

Material and construction choices matter

Not every site needs the same filter build. The right choice depends on what the system is trying to do, how much dust is present and how the filter sits in the frame.

Common considerations include:

• •media type and dust-holding characteristics
• •initial resistance and how it behaves as dust loads up
• •rigid or pleated construction
• •sealing method to reduce bypass at the frame
• •availability of washable or non-washable options
• •resistance to the temperatures, moisture and contaminants present at the site

Some filters are designed to be washable - check the product instructions. For many older systems, though, the priority is a replacement that matches the original installation and can be maintained without changing the rest of the equipment.

If you are comparing product types, our products and custom air filters are useful starting points.

Keeping older systems operational without overcomplicating maintenance

One advantage of custom filters is that they can reduce the need for makeshift fixes. A well-matched filter is easier to install correctly, more likely to seal as intended and less likely to be damaged during routine changeout.

That can matter in sites where downtime is difficult to manage. For example, in plant rooms with limited access, a filter that fits properly can make servicing simpler and reduce the chance of repeated callbacks caused by a poor fit.

It also helps to keep a record of what has been supplied. For older sites, maintaining a simple file of measurements, photos, part details and installation notes can make future ordering easier, especially if the equipment is discontinued or the original paperwork is incomplete.

Inspection frequency depends on the system, site conditions and dust load. Follow the filter and equipment manufacturer instructions, and monitor pressure drop where gauges are fitted. For sites with more demanding maintenance needs, filter servicing and commercial filter servicing may also be useful.

Working with contractors and buyers on hard-to-source filters

For mechanical contractors and industrial buyers, the best result usually comes from treating the filter as part of the system, not just a consumable item. That means checking the housing, the access method, the airflow direction and the physical space before selecting the replacement.

A practical ordering process often includes:

• •confirming whether the old part number is still valid
• •measuring the housing rather than relying on guesswork
• •identifying whether a standard frame can be reused
• •checking whether the filter needs to fit an existing seal or retaining clip
• •confirming the required quantity and lead time before shutdown work begins

If the site is spread across multiple buildings or has different plant rooms, it can help to document each location separately. That avoids confusion when similar-looking filters are actually different sizes or constructions.

For buyers who manage multiple sites, industries we supply may help you quickly identify the type of environment you are dealing with and the likely filter requirements.

A practical solution for older buildings

Older buildings and discontinued systems do not always need a full plant replacement to stay functional. In many cases, the right custom filter is enough to keep the existing setup working as intended while preserving the housing, the access arrangement and the building fabric.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. If you need a filter for an older site, a discontinued system or a hard-to-source application, we can help supply or make the right fit. Call 07 3800 3448 or request a quote.