An F7 filter helps reduce pollen, fine dust and PM1/PM2.5 particles in incoming MVHR air. This practical guide explains where the filter goes, how F7 compares with G4 and activated carbon filters, and when it should be replaced.
An F7 filter is the fine-particle filter used on the incoming-air side of many MVHR and heat recovery units. Its job is to reduce pollen, fine dust and a meaningful share of PM10, PM2.5 and PM1 before outdoor air reaches your rooms.
This guide shows where it goes, what the percentages mean, when it is worth using and when an activated carbon filter is the better answer.
Use an F7 or tested ePM1 filter on incoming supply air when pollen and fine outdoor particles are the problem. Use G4 or ISO Coarse mainly for unit protection. If smoke or traffic smell is the problem, choose a compatible combination filter with activated carbon and expect a shorter 2–3 month useful life.
F7 is the familiar name from the older EN 779 classification. The letter F meant fine filtration, and 7 was the class number. You will still find F7 in older ventilation manuals, replacement-filter lists and normal product searches.
The current ISO 16890 system uses labels such as ISO Coarse, ePM10, ePM2.5 and ePM1. Instead of one letter and number, it identifies the tested particle-size fraction and the measured efficiency group. That makes a label such as ePM1 60% more useful than F7 alone.
An ePM1 60% filter achieved 60% efficiency for the standardized PM1 fraction in the laboratory test. PM1 covers particles with an optical diameter from 0.3 to 1 micrometre. Real-life performance also depends on airflow, installation, outdoor air and filter loading.
For a tested high-performing F7 replacement, the practical figures can look like this:
These figures belong to a tested filter with that performance. They are not a universal promise for every product sold under the old F7 name.
Some original Zehnder ComfoAir Q filters are declared ePM1 50%, while a compatible replacement can be tested at ePM1 60%. See the Zehnder ComfoAir Q 350, 450 and 600 F7 + G4 replacement set.
An F7 filter is a particle filter. Installed on the incoming-air side, it can reduce the amount of airborne particles entering the home. It does not remove gases, VOCs or odours.
PollenLarge seasonal airborne pollen particles
Traffic particlesBrake, tyre and road dust — not exhaust gases
Combustion particlesFine particles from wood burning and heating smoke
Smog particlesParticulate pollution — not the gaseous components
Mould sporesAirborne spores entering with outdoor air
Fine dustA meaningful share of PM10, PM2.5 and PM1
Agricultural dustField and pesticide dust particles — not pesticide vapours
Respiratory dropletsSome particle carriers released by coughing or sneezing
In the usual residential arrangement, F7 goes on the incoming outdoor-air or supply-air side. It filters air before it passes through the unit and enters bedrooms and living spaces. The extract-air filter catches household dust before extracted indoor air reaches the heat exchanger.
This is the common F7 + G4 arrangement, not a universal rule. Some units use F7 on both sides. Follow the model diagram and labels.
Mixed F7 + G4 sets are used in units including Aldes InspirAIR Home SC 240 and InspirAIR Side 240, Salda Smarty 2XP and Siber DF EVO and OPTIMA.
Install the filter in the direction shown by the arrow on the frame or unit. If it is fitted backwards, the pleats and support structure may not work as designed, which can cause uneven loading and shorten the filter’s useful life.
If there are gaps between the filter and its holder—or openings around the filter frame—air will take the easier path around the filter media. Part of the air will then remain unfiltered, so the F7 classification provides little benefit.
| Filter | Main job | Practical particle guide | Typical use | Main drawback |
|---|---|---|---|---|
| G4 / ISO Coarse | Protects the unit from insects, fluff and large dust | Often under 5% for PM2.5 | Extract side or pre-filter | Very limited fine-particle capture |
| M5 / ePM10 | Intermediate particle filtration | Often 50–70% PM10 and up to about 15% PM2.5 | Middle option | Weak on the finest particles |
| F7 / ePM1 | Pollen and fine particles | A tested ePM1 60% example may reach about 75% PM2.5 and 90% PM10 | Incoming supply air | More resistance and cost than G4 |
| F9 | Higher fine-particle efficiency | Often starts around ePM1 85% | Very polluted locations when approved | Higher resistance |
| Carbon combination | Particles plus odours and some gases | Often ePM10 or ePM2.5 media with carbon fibre | Smoke and traffic odours | Usually weaker fine-particle capture and short carbon life |
| HEPA | Very high particle filtration | Separate high-efficiency classification | Systems designed for HEPA | Too much resistance for most residential MVHR units |
An activated carbon filter for a residential MVHR unit is normally a combination filter, not a block of carbon and not a separate cassette filled with carbon. Like many automotive cabin filters, it uses ePM10 or ePM2.5 filter media manufactured with activated carbon fibre integrated into the material. The same pleated medium catches solid particles while the carbon fibre adsorbs part of the odours and gaseous pollutants.
Your main problem is pollen, fine road dust, PM2.5 or combustion particles.
Your main complaint is wood-smoke smell, traffic exhaust smell or other outdoor odours.
The particle media may be ePM10 or ePM2.5 rather than ePM1, so fine-particle capture can be lower than with F7.
Carbon has limited adsorption capacity. Once saturated, it stops holding odour molecules effectively even if it does not look dirty. 2–3 months is a sensible practical replacement interval for many thin carbon-fibre filters.
Changing from G4 to F7 is most relevant near busy roads, city centres, industry or construction, and where solid fuel is burned during the heating season. It is also useful during pollen season.
Do not expect an immediate smell or dramatic overnight feeling. PM2.5 and PM1 pollution is often invisible and odourless. If smell is the only problem, use carbon rather than expecting F7 to solve it.
If a unit was designed only for G4, extra resistance can reduce airflow, increase fan noise, trigger an error or leave the home under-ventilated.
Avoid unknown-origin filters without a test declaration. Also avoid stretching a small sheet of F7 media over a wire frame: too little surface area creates high resistance.
Some units use a dedicated supply filter, such as the Brink Sky 150 and Sky 200 ePM1 60% filter. The Brofer RDCD25SK and RDCD25SH set contains one ePM1 60% and two ISO Coarse filters.
Practical starting interval under normal residential conditions.
High particle load: busy roads, construction dust, heating-season smoke or a strong pollen season.
Inspect the filter after an airflow warning, increased fan noise or visibly heavy loading.
Check earlier if airflow falls, fan noise increases, a warning appears, rooms feel stale or condensation starts appearing. Do not judge only by colour because fine particles load inside the media.
Residential F7 filters are disposable. Vacuuming does not restore the inner media; washing or compressed air can damage it.
Read How to replace MVHR filters and Supply Air, Extract Air and AIRFLOW markings explained.
These examples use fine supply-air filtration, but their set layouts differ. Check the complete model name, dimensions and number of filters before ordering.
Zehnder ComfoAir Q, Aldes InspirAIR 240, Salda Smarty 2XP, Siber DF EVO, Brink Sky and Brofer RDCD25SK / SH.
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Choose F7 or tested ePM1 when pollen and fine particulate pollution are the problem and your unit supports the resistance. Choose a carbon combination when odour and gaseous pollution are the complaint. Use G4 for unit protection where the design calls for it.
Send the MVHR model, a photo of the old label and the dimensions. We will check the correct set.
