Can You Compare Old G and F Grades with ISO 16890?

If you still see G3, G4 or F5 to F9 on drawings, asset lists or filter labels, you are not alone. Many sites in Australia still manage older EN 779-era specifications even though ISO 16890 is now the current classification system, which can make replacement sourcing confusing.

The short answer is that you can make a practical comparison, but you should not treat old G and F grades as a direct one-to-one match with ISO 16890. The safest approach is to compare the filter’s real application, required particle capture range, system resistance and physical size, then confirm the replacement with the mechanical services engineer or building owner.

Why old G and F grades still show up

EN 779-era grades were widely used for many years, so older maintenance records, service tags and equipment schedules still refer to them. In practice, that means contractors and facility teams often need to source a replacement for a filter that was originally specified as G4, F7 or something similar.

That can be awkward because the old grade does not always tell you everything you need to know. Two filters with the same grade can still differ in media type, depth, frame construction, dust holding capacity and airflow resistance.

That is why a practical cross-reference is useful, but only as a starting point.

What changed with ISO 16890

ISO 16890 classifies filters by the percentage of particulate matter they capture in different size ranges, rather than by the older G and F labels. In simple terms, it gives a more detailed picture of how a filter performs on airborne particles of different sizes.

For replacement work, that means you will often need to think in terms of the application and the air handling system rather than chasing an exact legacy number.

A practical way to compare old G and F grades

If you are trying to replace an old filter spec, start by treating the old grade as a performance clue rather than a final answer.

A useful field approach is:

• •identify the old grade on the filter or drawing
• •measure the filter dimensions carefully
• •check the frame style, seal type and media depth
• •review the unit’s airflow and pressure drop requirements
• •confirm whether the filter is pre-filter, final filter or a staged filter
• •compare the site’s indoor air quality needs and dust loading

If you are not sure of the size, our guide on how to measure an air filter can help avoid ordering the wrong frame dimensions.

General legacy-to-modern comparison approach

Without turning this into a conversion table, the broad way to think about it is:

• •G grades were usually used for coarse filtration and pre-filtration duties
• •F grades were used where a finer level of particle capture was needed
• •ISO 16890 replacement selection should be based on the intended use, not only the old grade label

In many HVAC systems, an older G4 may be replaced by an ISO 16890 ePM or coarse-rated product depending on the application, while an older F7 or F9 may need a finer ISO 16890 option. The exact selection depends on the plant, the duty and the OEM or consultant requirement.

What details matter more than the old grade

When sourcing replacement filters, the grade on its own is only one piece of the puzzle. For contractors and buyers, these are often the details that matter most.

Filter dimensions and fit

A correctly sized filter is essential. Even a filter with the right performance band can be unsuitable if it does not seal properly in the frame or cassette.

Check:

• •overall length, width and depth
• •flange or header style
• •gasket arrangement
• •front and rear access clearance
• •whether the filter is rigid, pleated or bag style

If the dimensions are unclear, compare the existing unit against the equipment drawings or measure the opening directly. For custom or unusual sizes, custom air filters may be the most practical option.

System resistance and airflow

Replacement filters should suit the system’s operating conditions. A filter that is too restrictive for the fan and ductwork can create avoidable pressure drop, while a filter that is too open may not meet the intended filtration duty.

For sites with gauges or pressure switches, monitor pressure drop and replace filters according to manufacturer instructions and site conditions rather than relying on a fixed schedule.

Dust load and site conditions

A plant room in a coastal, industrial or high-dust environment will often behave differently from a lightly loaded office system. The replacement filter choice should reflect what the system is actually dealing with, not just the nameplate specification.

When ISO 16890 is enough, and when it is not

ISO 16890 is the current classification language, but that does not mean the old specification can be ignored overnight.

It is usually enough to work from ISO 16890 when:

• •the equipment manual already lists ISO 16890 classes
• •the site is undergoing a documented upgrade
• •the filter supplier can match the application and size accurately
• •the mechanical services engineer has confirmed the required filtration level

It is not enough on its own when:

• •the old filter was part of a multi-stage arrangement
• •the unit has tight space or unusual sealing requirements
• •the installation is tied to a specific OEM design
• •the building owner wants the replacement to match an existing maintenance standard

For ventilation projects, site requirements should be confirmed with the mechanical services engineer or building owner, including any relevant expectations under AS 1668.2:2024.

Special cases: pleats, bags, washable products and HEPA

Not every replacement is a simple panel swap. Some systems use bag filters, compact pleats or deeper frames that were selected for dust holding or service access reasons.

A few points to keep in mind:

• •some filters are designed to be washable - check the product instructions
• •washability does not mean every washable-looking filter can be cleaned and reused safely
• •a deeper filter may change resistance and fit even if the nominal grade seems similar
• •HEPA filters are a separate category and should not be mixed up with general HVAC grades

If you are dealing with HEPA applications, the relevant standard is EN 1822, where H13 is at least 99.95% and H14 is at least 99.995% efficiency at the most penetrating particle size. That is a different discussion from the old G and F grades.

A practical sourcing checklist for contractors and buyers

When you need a replacement quickly, a good brief saves time and reduces back-and-forth.

Include:

• •the old grade if known
• •the exact dimensions
• •the frame type and seal arrangement
• •the equipment make and model
• •the installation location
• •whether the filter is a pre-filter or final filter
• •any pressure drop or airflow constraints
• •photos of the existing filter if available

If the site has multiple air systems, keep the labels consistent so maintenance teams can identify the correct product later. That can make future filter servicing or commercial filter servicing much easier to manage.

Need help matching an old specification?

Total Air Filtration is a family-owned air filter manufacturer and supplier based in Hillcrest, Brisbane QLD. If you are trying to replace an older G or F grade filter with an ISO 16890 equivalent, we can help assess the size, fit and application so you can order with more confidence.

Call 07 3800 3448 or request a quote. You can also browse our products or get in touch through contact us.