The Short Answer: G4 and F7 Are No Longer Valid Classes
Codes such as G4, M5 and F7 belong to EN 779. That standard was withdrawn in 2018 and replaced by ISO 16890, which classifies filters not by G/M/F letters but against real atmospheric particle fractions: ISO Coarse, ISO ePM10, ISO ePM2.5 and ISO ePM1.
The old codes are still widely used in conversation and still appear in specifications. But ordering a filter as "F7" today does not fully define what you are buying.
What Did EN 779 Classes Measure?
EN 779:2012 divided filters into three groups:
- G1–G4 (coarse): Measured by gravimetric arrestance using synthetic dust — that is, how many grams of dust the filter retained, not which particle sizes it captured.
- M5–M6 (medium): Measured by efficiency against 0.4 µm DEHS aerosol, with no minimum requirement.
- F7–F9 (fine): Also 0.4 µm efficiency, with an additional minimum efficiency requirement after discharge.
The problem was this: in the coarse classes, measurement was by weight. A filter that retained a great deal of dust by mass might capture almost none of the fine particles that matter most for health. The standard did not make that visible.
What Does ISO 16890 Do Differently?
ISO 16890 evaluates a filter against the real atmospheric particle distribution rather than a laboratory dust. It is built on the PM10, PM2.5 and PM1 fractions used in air quality measurement:
- ISO ePM1: Efficiency against particles in the 0.3–1 µm range — soot, exhaust particulate and bacteria-sized loads.
- ISO ePM2.5: The 0.3–2.5 µm range.
- ISO ePM10: The 0.3–10 µm range — pollen, coarse dust, spores.
- ISO Coarse: Filters meeting none of the above thresholds; reported as gravimetric arrestance.
To fall into a group, a filter must achieve at least 50% efficiency in that fraction. The result is stated in 5% steps, for example ISO ePM1 60%.
The Most Important Difference: Discharged Measurement
Most filters with synthetic media carry an electrostatic charge. That charge raises efficiency markedly while the filter is new, but it dissipates in service through humidity and captured particulate.
The coarse and medium classes of EN 779 did not account for this; a filter could show high efficiency in the laboratory and settle to a far lower level within months in service. ISO 16890 repeats the measurement on media discharged (conditioned) with isopropanol and reports that value as well.
The practical consequence: a filter sold as "F7" under the old standard may report a lower ePM1 value than expected when tested to ISO 16890. This does not mean the filter has become worse — it means the measurement has moved closer to reality.
Is There a Conversion Table Between the Two Standards?
No. An exact conversion is not possible, and tables claiming otherwise are misleading. The two standards use different test dust, a different particle range and different conditioning; a filter's ISO 16890 class can only be established by retesting.
An approximate correspondence is nevertheless useful when reading specifications. The table below is indicative only and is not a conversion:
| EN 779 (former) | Typical ISO 16890 equivalent | Common use |
|---|---|---|
| G3 – G4 | ISO Coarse 45%–90% | Pre-filter, cassette filter, kitchen hood |
| M5 | ISO ePM10 50%–70% | Pre-filter, medium bag stage |
| M6 | ISO ePM2.5 50%–65% | Medium stage |
| F7 | ISO ePM1 50%–65% | Main stage, ahead of HEPA |
| F8 | ISO ePM1 65%–80% | Main stage |
| F9 | ISO ePM1 80%–90% | High-demand main stage |
Where Does EN 1822 Fit?
ISO 16890 does not cover the HEPA classes. E10–E12 (EPA), H13–H14 (HEPA) and U15–U17 (ULPA) fall under a separate standard, EN 1822, which remains in force.
The measurement logic differs as well: EN 1822 measures efficiency at the particle size where the filter is weakest — MPPS — and requires H13 and H14 filters to be individually scanned. For detail, see HEPA filters and the EN 1822 standard.
The US MERV system (ASHRAE 52.2) is a third scheme and cannot be compared directly with ISO or EN classes. For a comparison, see MERV 13 vs HEPA filter.
What to Consider When Selecting a Class
- Build a staged configuration. Trying to solve everything with a single filter clogs that filter rapidly. A coarse → medium → fine sequence optimises both cost and service life.
- Account for outdoor air quality. A facility near heavy traffic or industry raises the case for ePM1.
- Evaluate pressure drop alongside class. A higher class means higher fan energy. Eurovent energy classification is now based on ISO 16890.
- Ask for the discharged value. If a quotation gives only initial efficiency, field performance may differ.
- Verify old codes in specifications. Where a specification says "F7", request an ISO 16890 report from the supplier rather than proceeding on an assumed equivalence.
Safe Air Filter Solutions
Safe Air manufactures filters from the coarse stage through to fine. For the pre-stage see cassette filters, for medium and fine stages bag filters, and for high efficiency HEPA filters.
For the staging arrangement and class selection suited to your system, contact us.
Frequently Asked Questions
They are filter classes from the EN 779 standard. G1–G4 defined coarse filters by gravimetric arrestance, M5–M6 medium filters, and F7–F9 fine filters by 0.4 µm efficiency. EN 779 was withdrawn in 2018 and replaced by ISO 16890; although these codes are still used in conversation, they are no longer the valid classification.
EN 779 assessed coarse classes by gravimetric dust arrestance and did not account for the electrostatic charge that dissipates in service. ISO 16890 measures efficiency against real atmospheric particle fractions (PM1, PM2.5, PM10) and repeats the measurement on media discharged with isopropanol, so the reported value is closer to field performance.
There is no exact equivalent. F7 filters typically fall in the ISO ePM1 50–65% range, but this is indicative only. Because the two standards use different test dust, a different particle range and different conditioning, a filter's ISO 16890 class can only be established by retesting.
It means the filter captures an average of 60% of particles in the 0.3–1 µm range. To be classified in the ePM1 group, a filter must reach at least 50%; results are reported in 5% steps. This range covers soot, exhaust particulate and bacteria-sized loads, which makes it the most health-critical fraction.
No. The E10–E12 (EPA), H13–H14 (HEPA) and U15–U17 (ULPA) classes fall under EN 1822, which remains in force. EN 1822 measures efficiency at the particle size where the filter is weakest (MPPS) and requires H13 and H14 filters to be individually scanned.
