Filter Classes for Ventilation Systems: M5, F7, F9 & ePM Explained
M5, F7, F9 or HEPA – the right filter class is crucial for clean air, energy efficiency and the lifespan of your ventilation system. We explain the new ISO 16890 with its ePM values, provide clear recommendations for each application area, and show the most important replacement intervals.
The filter is the most underestimated component of the entire system: It determines which particles enter your living spaces, how hard the fan has to work, and how quickly heat exchangers and ducts become contaminated. Those who choose the wrong class or delay changing it pay with poorer air quality and higher electricity costs. This guide brings order to the jungle of old and new standard designations.
The old filter classes according to EN 779
For decades, the filter world was clearly organized: A letter indicated the filter category, a number the fineness within the category. From coarse dust filters through medium and fine dust filters to high-efficiency filters for cleanrooms, an ascending scale emerged – the higher the class, the smaller the particles separated.
You still constantly encounter these old designations: on equipment nameplates, in operating instructions, and in many product names. Therefore, it is worthwhile to know the old logic, even if it has been officially replaced. Until 2018, filters in Germany were classified according to EN 779:
| Class | Application |
|---|---|
| G2–G4 | Coarse dust filter (pollen entry, large particles) |
| M5–M6 | Medium dust filter (standard pre-filter) |
| F7–F9 | Fine dust filter (pollen, fine dust, smog) |
| H10–H14 | High-efficiency filter (HEPA, cleanroom) |
| U15–U17 | Ultra-high efficiency (ULPA, pharma) |
New standard ISO 16890: What the ePM values mean
The reason for the change in standards: The old test only incompletely reflected reality, as it evaluated filters based on a single particle size. ISO 16890 takes a more practical approach and measures how well a filter separates the particle size ranges that also play a role in outdoor air discussions – the familiar PM values from weather reports and environmental measurements.
For you as an operator, this is a real step forward: The new labeling directly indicates what the filter protects against – for example, pollen, fine dust, or particularly lung-penetrating ultrafine particles. Since 2018, ISO 16890 has been binding throughout Europe. It measures separation according to three particle sizes:
- ePM10 – 0.3–10 µm: Pollen, coarse dust
- ePM2.5 – ≤ 2.5 µm: Fine dust
- ePM1 – ≤ 1 µm: Bacteria, virus carriers
The percentage value after ePM indicates the separation efficiency. Example: ePM10 50% means the filter separates 50% of particles in the 0.3–10 µm range.
Conversion Old to New
| EN 779 (old) | ISO 16890 (new) | Application |
|---|---|---|
| G4 | Coarse dust (Coarse) | Air conditioning pre-filter |
| M5 | ePM10 50–60% | Standard residential pre-filter |
| M6 | ePM10 60–70% | Pollen protection for allergy sufferers |
| F7 | ePM1 50–70% | Residential final filter |
| F9 | ePM1 80–90% | High-performance final filter |
| H13 | HEPA | Operating rooms, cleanroom |
| H14 | HEPA | Pharma, semiconductor |
Which filter class for which application?
When choosing, a simple principle applies: as fine as necessary, not as fine as possible. Every finer filter stage increases the pressure drop in the system – the fan has to work harder, electricity consumption increases, and the filter clogs up faster. The right choice is therefore always a compromise between air quality, energy efficiency, and maintenance effort, tailored to the specific application location.
The two-stage concept has also proven effective: a coarser pre-filter captures the main part of the dust and thus protects the finer, more expensive final filter – this extends the service life of both stages.
Residential ventilation with heat recovery (KWL)
Standard for devices such as Nilan Compact, S&P CAD-HE and comparable ventilation systems:
- Standard setup: Outdoor air (supply air) ePM1 70% (old: F7), exhaust air ePM10 50% (old: M5) – the efficiency of the heat recovery remains optimal, with protection against pollen and fine dust
- Allergy sufferer setup: Outdoor air to ePM1 85% (old: F9), exhaust air remains ePM10 50% – maximum pollen and smog protection with slightly higher pressure drop
Basics for planning can be found in the guide Planning KWL: Comfort ventilation with heat recovery.
Clinic and Hospital
In medical facilities, significantly stricter requirements apply, as the protection of immunocompromised patients and germ-free working conditions are at stake. Multi-stage filter chains are common, where each stage relieves the next:
| Area | Filter stages |
|---|---|
| Common areas | F7 + F9 in series |
| Operating rooms | F7 + HEPA H13 |
| Cleanroom class 5/6 | HEPA H14 |
Commercial Kitchen
Attention: In commercial kitchens, flame arrestor filters according to DIN EN 16282-7 are mandatory above open cooking areas. Violations are punishable by fines of up to €50,000.
Replacement intervals: When does the filter need to be changed?
A filter does not work forever: With every hour of operation, particles accumulate in the filter medium, the pressure drop increases, and the volume flow of the system decreases. Eventually, the ventilation system supplies noticeably less air, the fan consumes more electricity – and a heavily loaded filter can itself become a hygiene weak point, for example, if microorganisms settle on moist dust.
Regular replacement is therefore not an option, but a prerequisite for healthy air and efficient operation. As a rule of thumb, these intervals apply:
| Filter class | Replacement interval |
|---|---|
| M5 / ePM10 50% | every 3–6 months |
| F7 / ePM1 70% | every 6–12 months |
| F9 / ePM1 85% | every 9–12 months |
| HEPA H13/H14 | every 12–24 months |
| Activated carbon | every 6–12 months |
Pro tip: For heavily polluted outdoor air (large city, industry, construction phase), change earlier. Optimal is a change as soon as the final pressure differential value is reached (stated on the filter data sheet). A complete overview of all intervals is provided in the Maintenance plan for ventilation systems.
Original or third-party?
When re-purchasing, the question quickly arises whether it has to be the original filter or if a cheaper replica is sufficient. Experience shows: The price difference is smaller than it seems – and the risks of a replica are often hidden, for example, with minimally deviating dimensions, through which unfiltered air bypasses the filter.
- Correct dimensions – no bypass air
- Guaranteed filter class according to standard
- Optimal service life
- Compatible with the manufacturer's warranty
Third-party (replica):
- Often incorrect dimensions – filter performance decreases
- Filter class not guaranteed
- Shorter service life
- Manufacturer's warranty may become void
Suitable original air filters as well as pocket and compact filters for central systems can be found in the shop. How to clean the entire system during a filter change is shown in the article Cleaning ventilation systems: DIY or specialist company?
Frequently asked questions about filter classes
What does "ePM10 50%" mean?
The filter separates at least 50% of particles in the size range 0.3–10 µm – this corresponds to the old class M5.
Which filter class for KWL with heat recovery?
Standard: Outdoor air ePM1 70% (old F7), exhaust air ePM10 50% (old M5). For allergy sufferers, outdoor air to ePM1 85% (old F9).
How often do I need to change ventilation filters?
M5/ePM10 every 3–6 months, F7/ePM1 every 6–12 months, HEPA every 12–24 months. Earlier in case of heavy pollution.
Are original filters more expensive?
Only 10–20% more – but they usually last 30–50% longer and filter reliably according to the standard.
What is HEPA?
High Efficiency Particulate Air, from class H13. Filters 99.95% of all particles ≤ 0.3 µm – including bacteria and virus carriers. Standard for operating rooms, cleanrooms, and pharmaceuticals.
Conclusion
With ISO 16890, you choose filters more precisely than ever before: Instead of abstract class letters, the ePM value directly tells you what the filter protects against. For residential areas, ePM1 70% in the supply air and ePM10 50% in the exhaust air are the proven standard; allergy sufferers upgrade the supply air to ePM1 85%. Just as important as the correct class is timely replacement – it ensures air quality, efficiency, and the lifespan of the system. You can find the right replacement filters for your system at any time on Wohnungstechnik.de.
