What Is a G4 Filter in Australian HVAC Systems?

If you are managing a building, buying replacement media, or specifying filters for a contractor, you may still come across the term G4. It is an older rating that remains common on legacy equipment and paperwork, even though newer standards are now widely used. Understanding what G4 means helps you choose the right replacement filter without guessing or over-specifying.

What G4 means in HVAC terms

G4 is an EN 779 coarse filter class. In practical terms, it was used to describe a lower-resistance pre-filter or general-purpose dust filter in air handling systems, fan coil units, return air setups, and some residential or light commercial HVAC applications.

You will still see G4 written on older system labels, maintenance schedules, and replacement filter records. In Australia, it often appears alongside other older EN 779 classes such as G3 and F5-F9. Although ISO 16890 has superseded EN 779, the older terms are still widely used in day-to-day buying and servicing conversations.

For facilities teams and contractors, the key point is this: G4 is not a brand name or a size. It is a performance class from an older rating system, so the actual replacement still needs to match the filter dimensions, frame type, thickness, sealing method, and airflow requirements of the equipment.

Where G4 still appears in Australian buildings

Older HVAC systems often keep their original documentation, and that is where G4 most commonly turns up. It may be printed on:

• •maintenance logs
• •asset registers
• •filter schedules
• •door labels on air handling units
• •drawings or commissioning documents
• •spare parts lists

You may also see G4 referenced when a building has been fitted out over time and different contractors have used different naming conventions. One site might describe a filter as G4, while another supplier lists the same style of replacement under a newer classification or by the physical build rather than the rating alone.

This is why it is important not to rely on the label by itself. A G4 reference tells you something about the intended filtration level, but not enough to order the right part without checking the size and construction.

How G4 relates to everyday replacement filters

In many residential and commercial systems, a G4 filter is simply a standard coarse replacement filter used to capture larger airborne particles before they reach more sensitive equipment components. That can include dust, lint, hair, and other everyday debris that can build up in ducted systems and mechanical plant.

The most useful way to think about G4 is as a replacement category, not a product name. The right replacement depends on the equipment and the site.

When matching a G4-style filter, check:

• •the exact length, width, and depth
• •whether it uses a metal, cardboard, plastic, or rigid frame
• •whether the filter sits in a slide track, rack, or holding frame
• •airflow direction markings
• •gasket or sealing requirements
• •available space and access for removal

If you are unsure how to measure the existing filter, our guide on how to measure an air filter is a useful starting point. If the filter is non-standard or the frame has been damaged, custom air filters may be the better option.

G4, modern ratings, and why terms are often mixed

Because EN 779 is older, procurement teams often face mixed terminology across suppliers, equipment manuals, and replacement stock. A contractor may ask for a G4 filter, while a manufacturer may list a product using a different classification system or describe it by application rather than rating.

That does not necessarily mean the filter is wrong. It usually means the language has changed over time.

For Australian sites, the safest approach is to confirm:

• •the original equipment specification, if available
• •the actual filter size and fitment
• •the service conditions, such as dust load and access constraints
• •any site-specific requirements from the mechanical services engineer or building owner

If your project involves ventilation design or compliance discussions, AS 1668.2:2024 may be relevant. Site requirements should be confirmed with the mechanical services engineer or building owner rather than assumed from the old filter class alone.

Choosing the right replacement for residential and commercial systems

A G4 reference is common in both residential and commercial settings, but the selection process can be different. In a small residential ducted system, the main concern may be getting the correct size and a filter that fits cleanly without bypass. In a commercial setting, access, dust loading, changeout practicality, and consistency across multiple units matter just as much.

When comparing options, consider:

• •whether the existing system uses a disposable or serviceable frame
• •whether the filter is part of a staged arrangement with pre-filters and secondary filters
• •how much dust or debris the site produces
• •whether the unit is exposed to construction, road dust, kitchen exhaust influence, or workshop conditions
• •whether the system has pressure gauges or differential pressure monitoring fitted

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. That approach is more reliable than using a generic calendar schedule.

Some filters are designed to be washable - check the product instructions. If a product is meant to be washed, it will be specified by the manufacturer. Do not assume that every reusable-looking filter is suitable for cleaning and reinsertion.

Practical buying tips for facility managers and contractors

If you are sourcing G4 replacements across multiple properties or units, consistency saves time. Create a simple record of the filter dimensions, frame style, and any notes about access or sealing so the next replacement is easier to identify.

It also helps to keep the following details on hand when ordering:

• •equipment make and model
• •existing filter thickness
• •exact opening dimensions, not just the nominal size
• •whether the filter is front-loaded, side-loaded, or accessed from a service door
• •whether the current filter has a rigid frame or a softer edge seal

For recurring maintenance work, filter servicing and commercial filter servicing can help keep replacements and checks organised. If you are specifying across several sites or property types, industries we supply gives a quick overview of the kinds of buildings and applications we regularly support.

When to ask for help

If a system is old, the documentation is incomplete, or the existing filter no longer matches current stock labels, it is worth checking before ordering. A small mismatch in frame depth, sealing, or orientation can cause installation issues and poor fit.

That is where a manufacturer and supplier can help interpret the old G4 reference and match it to a practical replacement for the actual unit on site.

Need help identifying a G4 replacement?

Total Air Filtration is a family-owned air filter manufacturer and supplier in Hillcrest, Brisbane QLD, established 2009. We can help supply or make the right replacement filters for your system, including older G4-style applications and custom sizes.

Call 07 3800 3448 or request a quote. You can also contact us if you need help confirming a size, checking a fitment, or matching an existing filter specification.