How to Create a Size Reference Sheet for Spare Air Filters on Site

Keeping a spare filter on hand is only useful if everyone on site knows exactly which one to order. A clear size reference sheet removes the guesswork by recording the approved dimensions, fit details and product notes in one place, so maintenance teams can check what is needed without measuring from memory or relying on old paperwork.

For facility managers and in-house maintenance teams, the goal is simple: create a reliable record that matches the filter in the equipment, not just what the old carton or label says. A good reference sheet saves time during reordering, helps avoid mismatched sizes, and makes it easier to keep track of what is installed across different areas of the site.

Why a size reference sheet matters

Air filters can look similar while having small differences in width, height, depth, frame style or sealing method. Those differences matter when the filter needs to fit correctly into an air handling unit, fan coil, cabinet or return air grille.

A written reference sheet gives your team a single source of truth. It is especially useful when:

• •more than one person orders replacement filters
• •the site has several systems with different filter types
• •the original equipment paperwork is incomplete or missing
• •you want a spare stock item that matches the installed filter exactly
• •contractors, cleaners or relief staff may need to identify the right item quickly

If your site uses filters in ventilation systems, it is also sensible to keep the sheet aligned with the equipment documentation and, where relevant, the requirements of AS 1668.2:2024. Site requirements should be confirmed with the mechanical services engineer or building owner.

What to record on the sheet

A useful size reference sheet does not need to be complicated. The key is to capture enough detail that someone else can reorder with confidence, even if they were not the person who first measured the filter.

Core details to include

Start with the basics that define the filter’s physical size and fit:

• •site name and area served
• •equipment name or tag number
• •filter location within the system
• •filter type or application, such as panel, bag, pleated or carbon filter
• •width, height and depth in millimetres
• •frame material, such as cardboard, galvanised steel, aluminium or plastic
• •filter media type if known
• •seal style or gasket detail
• •airflow direction, where marked
• •any part number shown on the frame or packaging
• •supplier name, if the item has been sourced before

If the filter has a special shape, note that clearly. Examples include odd-sized panels, deep pockets, filters with a retaining lip, or units that must slide into a specific rail or track.

Useful extra notes

A few extra comments can prevent confusion later:

• •whether the filter must fit a reusable frame
• •whether there is a handle, pull tab or open end that needs to face a certain way
• •whether there is limited clearance for removal and installation
• •whether the filter is intended for a particular room, process or piece of plant
• •whether the filter is a standard size or a custom air filter

If you are unsure whether a filter is a standard or custom size, compare the measured dimensions against the equipment space and the existing product markings. If the system needs a non-standard fit, custom air filters may be the best option.

How to measure and confirm the correct size

The best reference sheet is based on the installed filter, the available opening and the equipment instructions. Old packaging, handwritten labels or guessed sizes can lead to ordering the wrong item, so it is worth checking carefully before you record anything.

If you need a refresher on the measuring process, see how to measure an air filter.

Measure the filter and the opening

Measure the filter itself and, where practical, the space it sits in. This helps you confirm whether the listed size reflects the nominal size, the actual size or the opening size.

When measuring:

• •use a straight rule or tape measure and read in millimetres
• •measure width, height and depth at more than one point if the frame is not perfectly square
• •check for lips, flanges, frames or seals that affect the fit
• •note if the filter compresses slightly when installed
• •compare the removed filter with the cabinet or grille opening before writing the final dimensions

If there is any uncertainty, measure the opening and compare it with the current filter side by side. This is especially important when the site has old equipment, retrofitted housings or mixed brands.

Record the approved dimension, not just the observed one

A reference sheet works best when it captures the approved size, not only what was measured on the day. That means someone should confirm the entry before it becomes the site standard.

A practical approach is to:

• •measure the filter
• •compare it against the equipment space and part markings
• •confirm the details with the maintenance supervisor or site contact
• •record the approved size exactly as it should be ordered
• •save a photo of the installed filter label and fit, if possible

This is particularly helpful where there is more than one size used in a similar-looking cabinet. A small difference in depth or frame style can make the wrong filter seem correct at first glance.

Make the sheet easy to use on site

The best reference sheet is the one your team can actually find and use. Keep it short, clear and stored in a place that is accessible to the people who reorder parts or change filters.

Set up a simple template

You do not need fancy software. A shared document, spreadsheet or site folder is usually enough, as long as it is kept current.

A practical sheet should include:

• •equipment location
• •filter description
• •approved dimensions in millimetres
• •product or part code
• •quantity held as spare stock
• •supplier contact details
• •date of last verification
• •notes on installation or fit

It helps to use the same wording across the site. For example, always describe the same location the same way, such as “Plant Room A AHU 1” rather than switching between different names for the same unit.

Add a photo section if you can

A clear photo can prevent simple mistakes. Include one image of the installed filter in place and, if possible, one of the label or frame marking.

Photos are especially useful when:

• •the filter looks similar to several others on site
• •the frame has a unique clip, gasket or orientation
• •multiple people may need to identify the item quickly
• •the site has inherited equipment with incomplete records

A photo does not replace the written dimensions, but it gives the team a visual check before they place an order.

Keep the reference sheet current

A size reference sheet only works if it stays up to date. Sites change over time, and filters may be replaced by different models as equipment is upgraded or serviced.

Review the sheet whenever:

• •a new filter type is installed
• •a housing or frame is modified
• •a supplier changes the product specification
• •the site team finds a mismatch during replacement
• •the maintenance team notices a label or fit issue

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. If a filter is washable, only use that approach when the product instructions say it is suitable.

It is also worth keeping a note of which filters are used in different parts of the site, especially if some areas need finer filtration or specific media types. Our our products page can help your team match the right style to the application, while filter servicing and commercial filter servicing are useful references if your site uses scheduled maintenance support.

A simple process that avoids reordering mistakes

Once the sheet is in place, make it part of your normal maintenance routine. A straightforward process might look like this:

• •check the installed filter against the reference sheet
• •confirm the approved dimensions and part details
• •note any visible changes to the frame or seal
• •update the sheet if the installed item differs from the record
• •keep one person responsible for approving changes to the master copy

That small amount of discipline can save a lot of second-guessing later. It also helps new staff, contractors and relief workers identify the right replacement without needing to start from scratch.

Need help identifying the right filter size?

If you would like support checking dimensions, matching a replacement or setting up a reference sheet for spare stock, Total Air Filtration can help supply or make the right filters for your site. We are a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, and you can call 07 3800 3448 or request a quote.

If you are not sure what information to capture, contact us and we can help you work through the details before you reorder.