A G4 filter is a coarse grade air filter that captures at least 90 percent of dust by weight and stops particles of roughly 10 microns and larger. It is a first stage filter. Its job is not to deliver clean air at the end of the system. Its job is to take the beating so the expensive filter behind it does not have to.
That is the short answer. The longer answer is more interesting, because the letter and number printed on that filter belong to a European standard that was officially retired in 2018 and absolutely refuses to leave.
Three standards, one shelf
Filter grades are confusing for a reason that has nothing to do with you. Three classification systems grew up independently on three continents, they measure different things using different test dusts, and all three now turn up on the same supplier shelf in Australia.
- EN 779 is the European system. It gave us G1 to G4 for coarse filters and M5 to F9 for the finer grades. This is where G4 comes from.
- MERV is the North American system, published by ASHRAE. It runs from MERV 1 to MERV 20 and shows up on imported filters and anything bought through an online marketplace.
- ISO 16890 is the international standard that replaced EN 779. It classifies filters by how well they capture particulate matter fractions, using the same PM language air quality reports use.
- AS 1324.1 is the Australian standard for air filters used in general ventilation and air conditioning.
Product labelling mixes these freely. Your booth installation spec might reference G4 while the panel filter in the box carries a MERV number and the data sheet quotes ISO 16890. If you have ever ordered what you were promised was a G4 and received something with the structural conviction of a tea bag, inconsistent grading is usually the explanation.
The standard that retired but never actually left
This is the part most guides skip, and it is the part that causes real ordering mistakes.
ISO 16890 was published in December 2016 and replaced EN 779 on 1 July 2018. It did not simply rename the old grades. It scrapped them. Under ISO 16890 there is no G4 and no F7. There are four groups instead: ISO Coarse, ISO ePM10, ISO ePM2.5 and ISO ePM1. Efficiency is now measured against particle size fractions rather than against the weight of a synthetic dust.
So where did G4 go? Into ISO Coarse. A filter that cannot capture at least 50 percent of the ePM10 fraction gets classed as ISO Coarse and given an arrestance figure, which is how you end up reading something like ISO Coarse 90 percent on a current data sheet.
And yet G4 is still everywhere in Australia. It is in booth manuals, installation specifications, maintenance schedules, WHS documentation and half the supplier catalogues in the country. That is not laziness. Equipment outlives paperwork, and a booth commissioned in 2004 still has a 2004 specification pinned to the wall beside it.
The important caution: there is no exact conversion between the two systems. Two filters that were both G4 under EN 779 can land in different ISO 16890 classes, because the tests are asking genuinely different questions. Any crossover table you find, including the one further down this page, is indicative only.
Practically, that means two things. If your specification says G4, keep ordering to G4 so your paperwork stays consistent. And when the supplier data sheet quotes ISO Coarse instead, that is not a mismatch or a substitution. It is the current standard doing its job. Ask for the arrestance figure so you can compare like for like.
What a G4 actually catches
| Particle Type | Approximate Size | Captured by G4? |
| Coarse dust, grit and sanding debris | 50 microns and above | Yes |
| Lint, fibres and insects | 10 microns and above | Yes |
| Pollen | 10 to 100 microns | Mostly |
| Larger mould spores | 10 to 30 microns | Partly |
| Fine dust and paint mist | 1 to 10 microns | No |
| Fine overspray | under 5 microns | No |
| Bacteria | 0.3 to 10 microns | No |
Read the bottom half of that table twice before you rely on a G4 on its own. It is a first line of defence, not a last one, and the difference is the whole point of the grade.
Where a G4 belongs
In an HVAC system
A G4 sits at the first stage of an air handling unit, ahead of the bag, pocket or high efficiency final filter. It catches the bulk material so the fine filter behind it can spend its life doing fine filtration rather than catching leaves.
It is also protecting hardware. Coils are expensive, awkward to reach and miserable to clean in place. A G4 is a consumable that stands between the outside world and a capital item.
In a spray booth
A G4 typically sits in the intake or ceiling section, capturing environmental dust before conditioned air ever reaches the work. Downstream, the exhaust stage handles overspray. A well maintained G4 in front noticeably extends the life of the filters behind it, because it absorbs the coarse loading they would otherwise have to hold.
In both cases the principle is identical. The G4 is the cheap thing that protects the expensive thing
G4 filter material: what is actually inside
Two filters can carry the same grade and behave completely differently in service. The grade describes a test result. The media describes what happens in your plant room at 2pm in February.
Media types
- Synthetic polyester is the workhorse of industrial G4. Good dust holding capacity, low resistance to airflow, tolerates humidity well.
- Glass fibre offers higher initial efficiency and appears in some original equipment applications, but it is more fragile and much less common as roll stock.
Formats
- Panel filters arrive pre framed in fixed or custom dimensions and drop straight into a housing.
- Pocket or bag filters carry far more media area in the same opening and suit high volume HVAC.
- Roll media comes in continuous lengths and is cut to size, either by you or by the supplier.
Frames
- Cardboard is cost effective and perfectly adequate for single use in most intake positions.
- Galvanised steel suits humid environments and anywhere with solvent exposure.
- Aluminium is the durable option for permanent housings with replaceable media pads.
Why the cheap ones cause trouble
Low quality G4 media often has uneven fibre distribution, which creates pinhole weak points where particles simply pass through. Some media delaminates under sustained airflow, and loose media fragments arriving in a spray booth will ruin a finish faster than the dust you were trying to stop. Thin cardboard frames can buckle under negative pressure, jamming the holder and disturbing airflow across the whole bank.
The grade on the label tells you what a filter should do. The media tells you what it will do. Ask for the data sheet.
G4 vs MERV vs ISO ePM: the crossover table
| EN 779 grade | ISO 16890 group (indicative) | MERV (approx) | Typical role |
| G3 | ISO Coarse 60 to 80 percent | MERV 5 to 6 | General ventilation prefilter |
| G4 | ISO Coarse 90 percent or higher | MERV 7 to 8 | HVAC first stage, spray booth intake |
| M5 | ISO ePM10 50 to 65 percent | MERV 9 to 10 | Secondary filtration |
| M6 | ISO ePM10 70 to 80 percent | MERV 11 to 12 | Secondary filtration |
| F7 | ISO ePM1 50 to 65 percent | MERV 13 | Air handling unit final stage, booth exhaust |
| F8 | ISO ePM1 70 to 80 percent | MERV 14 to 15 | High specification industrial |
| F9 | ISO ePM1 80 to 90 percent | MERV 15 to 16 | Critical supply air |
| H13 | EN 1822, outside ISO 16890 | MERV 17 and above | HEPA, cleanroom and healthcare |
Indicative only. MERV measures efficiency across 0.3 to 10 microns, EN 779 measured arrestance by dust weight, and ISO 16890 measures efficiency against PM fractions. Three different questions produce three different answers. Use this table to get into the right neighbourhood, then compare data sheets properly.
Which standard applies in Australia?
AS 1324.1 is the domestic standard covering air filters for general ventilation and air conditioning. Alongside it, European grades remain widely specified and widely understood across Australian HVAC, industrial and spray booth work, and ISO 16890 is what most current data sheets are issued against.
For spray booths, AS/NZS 4114 covers design, construction, installation and maintenance. Check which edition your own documentation references before quoting it in a specification, because the standard has been revised since the versions many older booth manuals cite.
The practical advice is unglamorous but it saves real pain: make your documents agree with each other. If the installation specification, the maintenance schedule and the purchase order all say G4, keep them all saying G4, and hold the supplier data sheet alongside them. Audits and insurance reviews go a great deal faster when nothing contradicts anything else.
Buying a G4 in Australia
Panel, pocket or roll?
Panels are fastest when the housing takes a standard size, or when you order the exact size you need. Roll media suits adjustable frames, unusual dimensions and anyone cutting on site. Pocket filters belong in high volume HVAC where media area matters more than unit price.
The sizes that are not standard
Plenty of Australian installations run common panel dimensions. Plenty do not, particularly older booths, imported air handling plant and anything that has been modified on site over twenty years.
Trimming a framed panel down to fit is the wrong fix. You break the frame, leave the media edge unsealed and create exactly the bypass path the filter exists to prevent. Order the size you need, or buy roll media that is designed to be cut.
What to have ready before you order
- The housing opening measured in millimetres: length by width by depth
- Frame type required: cardboard, galvanised steel or aluminium
- The grade you need and which standard your specification quotes it against
- How many filter positions the system has
- The downstream filter specification, so both stages are ordered together
How often should a G4 be changed?
There is no universal figure, and anyone who gives you one without asking about your site is guessing. It depends on operating hours, how dirty the incoming air is and the air volume moving through the bank.
Visual inspection monthly is a reasonable habit in active or dusty environments. Better still, work from a pressure differential rather than the calendar. If the system has a Magnehelic gauge or a pressure sensor across the bank, a steady rise in pressure drop is the most reliable signal you will get.
Do not let finish quality be the thing that tells you a filter is blocked. By that point the filter has already cost you a job.
G4 filter FAQs
Is a G4 filter the same as a MERV 8?
Approximately, but not exactly. They sit in a similar performance band, but they are tested under different standards using different dusts, so they are not interchangeable on paper. Where your documentation references European grades, specify the European grade.
Is G4 still a current grade?
Not under ISO 16890, which replaced EN 779 in July 2018 and retired the G and F classes. G4 remains in common trade and specification use across Australia, and suppliers still sell to it, but a current data sheet will most likely express the same filter as ISO Coarse with an arrestance percentage.
Are G4 filters washable?
Most are not. Standard disposable synthetic and glass fibre G4 media is built to be replaced, not cleaned. There are washable panel filters made to a G4 equivalent using heavier synthetic or metal mesh media, and those are sold specifically as washable, so the product description will say so plainly.
If it does not say washable, treat it as disposable. Washing disposable media collapses the fibre structure and strips whatever loft was holding the dust. The filter comes out looking clean and performs noticeably worse than a new one, which is the worst of both outcomes.
Can I run a G4 on its own?
Only if coarse filtration is genuinely all the application needs. A G4 will not capture fine dust, paint mist or overspray, so in a spray booth or any system with a clean air requirement it is the first stage of a set, not the whole set.
What is the difference between a G4 panel and G4 roll media?
A panel is pre framed at a fixed size and drops in. Roll media is supplied in continuous length and cut to fit, which suits adjustable frames and unusual openings. Both can be made to G4. The right choice comes down to your housing design and whether you would rather spend money or minutes.
What does the G in G4 stand for?
Grob, which is German for coarse. G1 to G4 is the coarse range under EN 779, and G4 is the top of it. The naming surprises people, but it makes sense once you know the standard came out of Europe.
Can I get a G4 in a size that is not standard?
Yes. Custom sizing is routine, not exotic, and it is the correct answer whenever the housing does not take an off the shelf panel. Send the housing measurements rather than the dimensions printed on the old filter.
Getting the right G4 for your system
If you know your sizes and you are working through a lot of positions, G4 media by the roll is usually the most economical route.
If your housings are not a standard size, or you would rather not stand at a bench with a blade, order it already cut.
Everything ships from Australian stock, so a booth or an air handling unit that is down does not wait three weeks for an overseas container. Send us the housing measurements and the grade your specification calls for and we will confirm availability and lead time.
