Air Filter Efficiency Classes: What Facility Managers Should Check Before Ordering

When it is time to reorder replacement air filters, the rating on the label is only one part of the decision. For commercial HVAC systems, facility managers, procurement teams and mechanical contractors also need to confirm the standard used, the actual dimensions, the filter depth, the frame construction and whether the product suits the equipment and site conditions.

Ordering by appearance or by a previous supplier description can lead to filters that fit poorly, load up too quickly or do not match the system’s intended performance. The notes below outline the main efficiency details to check before you place an order.

Start with the efficiency rating system used on the existing filter

Air filter efficiency can be described in different ways depending on the product and the standard used. That is where many ordering mistakes begin.

Before buying replacements, check whether the current filter is labelled under:

• •MERV rating
• •EN 779 class, such as G3, G4 or F5 to F9
• •ISO 16890 classification
• •HEPA designation for specialised applications

These rating systems do not convert directly from one to another. If the previous filter was specified using one standard, do not assume an equivalent class in a different standard will perform the same way in your system.

If the filter label is unclear, check the equipment manual, the building maintenance records or the label on the existing frame. If needed, how to measure an air filter can also help confirm the size details before you order.

Confirm what the filter is meant to do in the system

Efficiency should match the role of the filter in the air handling unit, fan coil unit or return air path. A pre-filter, final filter and specialty filter can all serve different purposes.

Ask these questions before ordering:

• •Is the filter there to protect equipment from dust build-up?
• •Is it the main filtration stage or a pre-filter ahead of a finer filter?
• •Does the system require low resistance, fine particle capture, or both?
• •Is the filter part of a standard commercial HVAC setup or a specialised application?

For buildings with specific ventilation requirements, confirm site expectations with the mechanical services engineer or building owner. If AS 1668.2:2024 is relevant to the project, it should be checked against the system design rather than assumed from the filter alone.

Check the actual dimensions and frame details

A filter with the right rating but the wrong size is still the wrong filter. Always confirm the nominal size and the actual size, because the printed label may not tell the full story.

Before ordering, verify:

• •length, width and depth in millimetres
• •whether the filter is rigid, pleated or panel style
• •frame material, such as cardboard, metal or synthetic construction
• •gasket or seal arrangement, if present
• •airflow direction, if marked on the filter

If the filter sits in a tight housing, small differences in depth or edge construction can affect installation. That can create bypass around the filter, which reduces the usefulness of the efficiency rating you paid for.

When a system uses a non-standard size, a custom air filters option may be more appropriate than forcing a near-match into service.

Match the media type to the site conditions

The efficiency class tells you part of the story, but the filter media also matters. Two filters with similar ratings can behave differently if their construction is not suited to the environment.

Consider whether the site has:

• •heavier dust loading from outdoor air intake locations
• •ongoing renovation or fit-out works
• •commercial kitchens, workshops or service areas nearby
• •moisture, condensation risk or humid conditions
• •odour control needs alongside particle capture

Some filters are designed to be washable - check the product instructions before reusing any filter. Others are intended for single use only, and washing them may damage the media or reduce performance.

If your site conditions change, the filter choice may need to change as well. A warehouse, office tower, school, health facility and retail tenancy can all place different demands on the HVAC system.

Understand what HEPA means before you order

HEPA filters are used in specialised applications where a very high level of particle capture is required. They should not be selected by assumption or substituted casually for general commercial HVAC filters.

If a project calls for HEPA, confirm the exact class:

• •H13: at least 99.95% efficiency at the most penetrating particle size, or MPPS, under EN 1822
• •H14: at least 99.995% efficiency at the MPPS under EN 1822

Those figures apply to the test method for that standard, so they should not be mixed up with general-purpose rating systems. If a higher-efficiency filter is being considered, check whether the fan can handle the resistance and whether the housing is designed for that filter type.

If you are unsure whether a HEPA-grade product is suitable, speak with the mechanical services engineer and confirm the specification before ordering.

Check resistance, dust loading and service access

A filter’s efficiency class is only useful if the system can run properly with it installed. Higher-efficiency filters often create more resistance to airflow than coarse filters, so the whole system should be reviewed rather than just the part number.

Before ordering, confirm:

• •whether the fan and housing suit the selected filter type
• •whether the system has pressure gauges or another way to monitor loading
• •whether there is enough access for safe change-out
• •whether the filter arrangement uses one stage or multiple stages

Do not rely on a fixed replacement schedule. 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 maintenance is outsourced, it can help to align ordering with filter servicing or commercial filter servicing so the replacement product matches the way the site is actually maintained.

Make sure the ordering information is complete

A clear purchase order reduces delays and avoids back-and-forth once the replacement is needed. Include enough detail for the supplier to match the correct product.

Useful ordering information includes:

• •filter dimensions
• •efficiency class and standard used
• •filter depth and frame type
• •quantity required
• •any special media or construction notes
• •site name and equipment reference if available
• •whether the filter is for a pre-filter or final stage

If you already know the product code, include that as well. If not, photographs of the existing filter label, the housing and the installed orientation can help.

For a broader look at what we supply, see our products or the industries we supply page if you are matching filters to a particular type of site.

Ordering the right replacement filter for your site

The most reliable purchase decisions come from checking the efficiency standard, the actual size, the media type and the application before you place an order. If the existing filter is no longer labelled clearly, do not guess. Verify the details first so the replacement matches the equipment and the site requirements.

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. We can help supply the right replacement filters or make filters to suit your system. Call 07 3800 3448 or request a quote. If you need help confirming details, you can also contact us.