How to Specify Replacement Filters for Repeat Orders

When a filter is replaced regularly, the easiest way to keep future orders accurate is to record the right details the first time. A clear specification helps facility teams, contractors and buyers order the same filter again without guesswork, and it reduces the risk of getting a unit that looks close but does not fit or perform the same way.

At Total Air Filtration, a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, we often help customers turn a one-off replacement into a repeatable ordering reference. The key is to capture the full filter description, not just the size.

Start with the exact dimensions and frame details

The first thing to record is the physical size of the filter, including the nominal size and, where possible, the actual outside dimensions. If the original filter was removed from a unit with a tight fit, even a small difference can affect installation.

When recording dimensions, note:

• •length, width and depth in millimetres
• •whether the size is nominal or actual
• •frame material, such as cardboard, plastic, galvanised steel or aluminium
• •the direction of airflow if the filter is directional
• •any special edge seals, gaskets or holding clips

If you are unsure how to measure a filter correctly, use how to measure an air filter as a reference when preparing your notes. It is also worth measuring the filter housing, especially if the original filter has compressed, bowed or been cut to fit.

Check whether the filter sits in a standard or custom frame

Some systems use standard sizes that are easy to repeat. Others rely on a non-standard filter or a custom frame made for a specific unit. If the original filter does not match a commonly available size, record that clearly and keep a sample or photo of the installed unit.

If the filter was supplied as part of a tailored solution, note the equipment model and the location in the plant or building. That makes future reordering much easier if the same unit is still in service.

Record the filter type and performance details

A repeat order should match more than the size. The filter media, construction and rating all affect whether the replacement is suitable for the application.

Useful details to record include:

• •the filter type, such as panel, pleated, bag, cartridge or cylindrical
• •the media type, if known
• •the rating system used on the original product
• •the frame style and depth
• •whether it is a pre-filter, final filter or a stage in a multi-stage arrangement
• •whether the filter is designed for dry use only or whether some filters are designed to be washable - check the product instructions

If your site uses air filtration terminology from different standards, keep the original wording on file. MERV, EN 779 and ISO 16890 do not convert directly, so avoid assuming one label is an exact substitute for another. In Australia, G3/G4/F5-F9 are still commonly referenced in older EN 779-based documentation, even though EN 779 has been superseded by ISO 16890.

Note any standards or project requirements

If the filter is being specified for a ventilation or air handling application, it may need to align with project documentation or site rules. For those situations, note any references to AS 1668.2:2024 and confirm the site requirements with the mechanical services engineer or building owner.

For specialised filtration, such as high efficiency applications, record the exact grade rather than a general description. For example, HEPA H13 is at least 99.95% and H14 is at least 99.995% efficiency at the most penetrating particle size under EN 1822. Use the exact grade specified by the equipment or project documentation, not a rough equivalent.

Capture the application and operating conditions

The same filter can behave differently depending on where it is used. A replacement order is more reliable when the specification includes the operating environment and the reason the filter was selected.

Helpful notes include:

• •the site type, such as office, workshop, production area or plant room
• •whether the system handles general ventilation, process air or dust collection
• •the approximate dust load or contamination source
• •whether the system runs continuously or intermittently
• •whether there are space constraints around the filter rack
• •whether the site has access limitations for installation or servicing

This information helps identify whether the original filter is still the right choice or whether a different construction would be better suited to the system. It is also useful if the plant is modified later and the filter needs to be reviewed.

Record inspection and replacement notes separately

Do not rely on a service schedule alone. Inspection frequency depends on the system, site conditions and dust load, and you should follow the filter and equipment manufacturer instructions. Where gauges are fitted, note the normal pressure drop reading so the next service team knows what to look for.

It helps to keep a separate field in the records for:

• •normal operating pressure drop
• •signs of loading or damage seen during inspection
• •any changes in dust, airflow or odour
• •whether the filter was changed as part of planned maintenance or after a fault

Make the repeat order easy for the next person

A good specification should still make sense to someone who was not involved in the original purchase. That means writing it in a way that is easy to search, share and verify.

Include the following in your internal asset or maintenance record:

• •equipment name and location
• •filter model or part number if known
• •full size and depth
• •filter type and rating
• •frame material and seal details
• •airflow direction if relevant
• •manufacturer or supplier notes
• •photo of the installed filter and label
• •date of last replacement and inspection notes

If you manage multiple sites, use the same naming format across the organisation. For example, keep the plant name, unit number and filter stage consistent so the wrong item is less likely to be ordered. A clear record also helps when comparing a stocked item against a replacement from our products or a made-to-order solution.

When the original filter is missing, damaged or unclear

Sometimes a repeat order starts with incomplete information. The original label may be faded, the filter may have been modified on site, or the previous supplier record may be missing key details. In that case, do not guess.

A practical approach is to:

• •measure the housing and any usable remnants of the old filter
• •photograph the unit from several angles
• •note the equipment make and model
• •record the old filter’s visible markings, even if partial
• •check whether the filter was installed in a standard holding frame or a bespoke arrangement
• •compare the old part with a sample from custom air filters if a standard size does not fit

If you are uncertain whether the replacement should match the original exactly or be revised for the current system, speak with the mechanical services engineer or building owner before ordering.

Build a simple repeat-order template

A brief template can save a lot of time at the next purchase. Keep it in your maintenance system, purchasing file or site logbook.

A useful template might include:

• •site and building name
• •plant or room location
• •filter type
• •size and depth
• •frame material
• •media or rating details
• •manufacturer part number or supplier reference
• •airflow direction
• •service notes
• •photo reference

Once this information is captured, future purchasing is much smoother. The person placing the order can compare the old specification with the replacement and spot any mismatch before the filter arrives.

Need help matching the original filter again?

If you want to make repeat orders easier, Total Air Filtration can help supply or make the right filters for your system. Call 07 3800 3448 or request a quote. You can also contact us if you would like help checking a specification before you place the next order.