What does a G4 filter do, and when is it enough? A practical guide to supply air, extract air, pre-filters, ISO Coarse and choosing between G4, M5 and F7.
A G4 filter catches larger dust, lint and other debris before it builds up inside your ventilation unit. It is a common choice for extract air, pre-filtration and, in some systems, incoming outdoor air too.
Is G4 enough for your home, or should you choose M5 or F7? Start with where the filter goes and what you want it to capture.
Choose G4 where coarse filtration is enough for the job. For finer filtration of incoming air, consider a compatible M5 or F7 option. Check your unit model before changing filter class.
Think about what travels through a ventilation unit. Outdoor air can carry dust, sand particles, fluff and insect fragments. Air extracted from your rooms carries household dust, hair and lint. G4 is there to catch the larger debris before it reaches the heat exchanger and other internal components.
Larger dustCoarse airborne dust and debris
Lint and fibresFluff, hair and household lint
Sand particlesLarger particles carried with outdoor air
Insect debrisInsects and larger fragments
That is useful work. A G4 filter is not simply a “worse F7”: it serves a different filtration need. It may also capture some larger pollen particles, but the G4 label alone is not a reliable basis for choosing a pollen filter. If pollen or fine particles from traffic and wood burning are your main concern, look at finer filtration and the actual filter data.
Every filter adds resistance to airflow. G4 is often used where coarse filtration is sufficient and there is no reason to add more resistance. What matters is that your ventilation unit can still deliver the airflow your home needs.
The filter class alone cannot promise lower noise, lower electricity use or a longer service life. Those depend on the unit, the filter design, the airflow and how dirty the filter becomes.
The same filter class can appear in different places. These simplified diagrams show the filtering sequence, not the internal layout of every ventilation unit. Follow your model’s instructions for the actual installation position.
Some MVHR units use G4 on the supply-air side. This can be suitable when coarse filtration meets your needs. But a G4 filter supplied with a new unit is not automatically the best choice for every home. A busy road, seasonal pollen or winter heating pollution may give you a reason to consider a compatible finer filter.
Use where the manufacturer permits it and coarse filtration is sufficient.
Looking for a coarse-filter set for your own unit? Browse the ventilation filter catalogue by unit model, or see the G4 sets below.
Extract air travels from your rooms through the unit and then outdoors. The filter catches household dust and lint before they can build up inside the unit. G4 is often enough for this job.
This is why a set can contain F7 for incoming air and G4 for extract air. The two filters have different jobs; they do not need to have the same class.
Here the filter’s main job is to protect the unit from indoor dust and lint.
This ZenAero compatible set pairs an F7 supply-air filter with a G4 / ISO Coarse extract-air filter for Zehnder ComfoAir Q 350, Q 450 and Q 600. Each filter measures 499 × 158 × 22 mm. It is a practical example of using finer filtration for incoming air while G4 protects the unit on the extract side.
In systems designed for two-stage supply-air filtration, G4 catches larger debris first. F7 then handles finer filtration. This can reduce the amount of coarse dirt reaching F7 and may help it last longer before it clogs.
Do not add an extra stage unless your unit is designed for it.
This ZenAero set contains one F7 filter and two G4 filters. It is compatible with the listed RDCD25SK / RDCD25SH series variants, not the plain RDCD25 or RDCD25e. Check your unit’s filter arrangement and full model code before ordering.
Start with the problem you are trying to solve. For an extract-air filter or pre-filter, the specified G4 may be exactly what you need. On the supply side, think about the particles you want to keep out of your rooms.
| Class | Main role | When to consider it |
|---|---|---|
| G4 | Coarse filtration of larger debris | Unit protection, extract air, pre-filtration or permitted coarse supply-air filtration |
| M5 | Medium filtration, generally finer than G4 | When you want improved capture of pollen and other larger airborne particles; compare product data |
| F7 | Finer particle filtration | Incoming air where pollen and finer traffic or combustion particles are a concern |
These are general roles, not fixed efficiency percentages or automatic ISO 16890 equivalents. Actual performance and airflow resistance depend on the filter.
M5 belongs to the medium-filtration group in the older classification. It can be worth considering when G4 does not provide the filtration you want. Compare the specific filter’s ISO 16890 rating and pressure drop rather than assuming that every M5 filter performs identically.
F7 is worth considering when pollen and smaller outdoor particles matter to you. But matching the dimensions is only the first check. Your unit must also be able to maintain the required airflow with that filter fitted.
For a closer look, read our F7 filter guide or the G4 vs F7 comparison.
In my own setup, I use F7 during the pollen season, when I notice hay fever symptoms. During the rest of the warmer period, I use G4 because dust from the nearby road clogs my F7 filter fairly quickly. In winter, when heating pollution becomes a concern, I switch back to F7.
This is a practical example of my own choices, not a recommendation to select a filter by the calendar alone. Choosing G4 also means accepting coarser filtration. Your local conditions, needs and permitted filter options may be different.
G4 comes from the older EN 779 classification. ISO Coarse belongs to ISO 16890, which also includes ePM10, ePM2.5 and ePM1 groups. G4 remains familiar because it still appears in unit instructions and replacement-filter descriptions.
The useful point for a buyer is this: there is no single “G4 equals ISO Coarse X%” conversion that applies to every filter. The test methods differ, so check the result given for the actual product. A percentage attached to ISO Coarse is not a promise to remove that same percentage of every pollutant in your home.
You do not need to memorise the standards to buy a replacement. Match the unit model, check the specified filter class and read the current product rating. Our guide to filter markings and airflow direction explains the labels you will encounter.
The easiest starting point is your ventilation unit’s exact model, including any version or suffix. Then work through these checks:
If you are unsure, send us the unit model and the dimensions of the existing filters. That is a better starting point than ordering something that only looks similar.
A fixed number of months would be convenient, but it would not suit every home. The same filter can clog faster beside a dusty road or building work than in a cleaner setting. How much you run the unit matters too.
Follow the manufacturer’s maintenance guidance and check the filter’s condition. Reduced airflow, more noise or a maintenance alert are reasons to inspect it. They do not prove that the filter is the only cause, but it is a sensible place to start.
Can you just vacuum it? Only if the manufacturer permits that for the particular filter or media. G4 describes a filtration class, not whether a filter is reusable. Vacuuming a disposable filter does not make it new again.
See our step-by-step MVHR filter replacement guide for the replacement process.
G4 makes sense where you need to catch larger debris and protect the unit. If you want finer filtration of incoming air, consider a compatible M5 or F7 option. Start with your unit model, then choose the filtration level that fits your home and the equipment.
These ZenAero compatible sets contain two G4 / ISO Coarse filters. Choose by the exact unit model and dimensions, not by filter class alone.
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Send the MVHR model, a photo of the old label and the dimensions. We will check the correct set.
