Reading the Small Print on Old HVAC Filter Labels Before You Reorder

If you are replacing an older HVAC filter, the label on the frame can be more useful than the old filter itself. The trick is knowing which details matter, which details are shorthand, and which details need checking against the equipment before you place an order.

For facility managers and contractors, reading the small print carefully can save time, avoid return visits, and help you match the right replacement the first time.

Start with the dimensions on the label

The first thing to look for is the listed size. On legacy filter labels, dimensions are often shown in millimetres or inches, and sometimes in a nominal format rather than the exact measured size.

That means a label might tell you the filter size, but the actual outside dimensions can be slightly different depending on the frame style and how the manufacturer labelled it.

When checking the label:

• •Look for length, width and depth, often written as three numbers.
• •Check whether the size is nominal or actual.
• •Confirm whether the filter is intended to fit a face opening, side access track or holding frame.
• •Compare the label against the slot or housing, especially if the old filter has swollen, bowed or damaged edges.

If the label is unreadable or missing, how to measure an air filter is a useful place to start before you reorder.

Read the depth carefully

Depth is one of the most commonly overlooked details on older labels. Two filters can have the same face size but very different depths, and they will not swap cleanly if the frame or holding system is built for a specific depth.

Depth can appear as a simple number such as 25 mm, 50 mm or 100 mm, but on some older product labels it may be abbreviated or grouped with the part number. In some cases, the depth is also tied to how the filter seals in the frame.

Pay attention to:

• •The stated depth on the label, not just the depth you estimate by eye.
• •Whether the filter has a rigid frame or a soft edge that compresses in the holding frame.
• •Any note that refers to pleat depth, media pack depth or nominal thickness.
• •Signs that the old filter was installed with spacers, clips or gaskets that affect the final fit.

If you are uncertain, measure the filter and the opening before ordering a replacement, or speak with a supplier who can help match the profile.

Identify the frame type and construction

Legacy labels often include a frame description that looks minor, but it can be critical. The same size filter may be available in cardboard, galvanised steel, aluminium, plastic or a rigid panel construction, and the wrong frame type may not suit the holding arrangement.

Frame type matters because it affects how the filter sits, seals and is handled during service.

Common wording on older labels may refer to:

• •Cardboard or paperboard frames
• •Galvanised or metal case frames
• •Aluminium frames
• •Plastic frames
• •Rigid panel construction
• •Soft-seal or gasketed edges

If the label mentions a seal or gasket, take note of it. That small detail can tell you whether the filter was designed to sit tightly in a specific housing, which is important when the system relies on a snug fit to avoid bypass around the filter edge.

When replacing legacy items, it is also worth checking whether the system has since been updated. A newer housing may accept a different frame style, but you should confirm the fit with the mechanical services engineer or building owner before changing the specification.

Make sense of part numbers and supplier codes

Part numbers are often the fastest way to identify an old filter, but only if you know how to read them. On some labels, the part number is a simple product code. On others, it may combine size, media type, frame type and an internal manufacturer sequence.

A useful approach is to separate the visible code into parts:

• •A brand or manufacturer prefix
• •A size or depth reference
• •A media or efficiency reference
• •A frame or construction code
• •A batch, revision or internal product sequence

The challenge is that older stock labels are not always consistent. The same style of filter may have had more than one code over time, especially if the product line changed or the manufacturer updated its catalogue format.

If the original label includes a part number, keep a clear photo of it and cross-check it against the filter itself, the equipment schedule and any old maintenance records you can find. If there is a product code but no clear size, do not assume the code alone is enough.

For replacement work across multiple sites or buildings, it can help to keep a simple record of the old code, the measured size and the frame description so the next reorder is easier.

Check the media type and rating references

Old labels may include a media description or a performance rating. These can be useful, but they need to be read carefully because different rating systems do not convert directly.

You may see references such as:

• •G3, G4 or F5 to F9, which are EN 779 classes still widely used in Australia
• •MERV ratings
• •ISO 16890 references
• •HEPA classifications on specialist filters

Do not try to convert one system directly into another without checking the product details. If a filter is specified by performance class, match it to the original requirement and confirm the application before changing it.

Where HEPA filters are involved, the label should be read with extra care. H13 is at least 99.95% efficiency, and H14 is at least 99.995% efficiency at the most penetrating particle size under EN 1822. If you are handling a HEPA application, it is wise to confirm the required grade and fit with the site specification before ordering.

Look for special notes that affect ordering

Older labels sometimes contain small notes that are easy to miss but very useful. These notes can save a wrong order if you catch them early.

Watch for wording such as:

• •Airflow direction arrows
• •Seal type or gasket note
• •Side load or front load note
• •Frame reinforcement details
• •Temperature or moisture notes
• •Washable or reusable wording, where applicable

Some filters are designed to be washable - check the product instructions before assuming a reused filter can be cleaned and put back into service. The label may also mention whether the filter is disposable or intended for a specific handling method.

You may also see references to a building standard or ventilation requirement. In those cases, confirm the site requirements with the mechanical services engineer or building owner, especially where AS 1668.2:2024 is relevant to the application.

When the old label is not enough

Sometimes the label is faded, the code is obsolete, or the filter has been replaced over the years with a similar-looking product. If that happens, rely on a combination of the old label, the measured size, the frame type and the equipment details rather than one clue alone.

A few practical steps can help:

• •Photograph the label before removing the filter.
• •Measure the filter and the opening.
• •Note the frame material and seal arrangement.
• •Record any part number, batch code or product name.
• •Check whether the installation has been modified since the original filter was fitted.

If the site uses multiple air handling units, keep each unit’s filter details separate. Similar-looking systems can still use different depths or frame styles, and mixing them up is a common cause of delays.

For larger maintenance programs, filter servicing or commercial filter servicing can help keep records current and make reordering simpler.

Need help matching an old filter label?

If you have an old label, a worn-out frame or a part number that no longer seems to line up with current stock, Total Air Filtration can help you identify the right replacement or make one to suit. We are a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, and we can assist with standard and custom air filters.

Call 07 3800 3448 or request a quote. You can also browse our products or contact us if you need help reading a legacy filter label before you reorder.