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HVAC filter grades explained: ISO 16890, G4 and F7

Updated 23 October 2026 · SEO Dons Editorial

How are HVAC air filters graded now?

Under ISO 16890 a filter falls into one of four groups, ePM1, ePM2.5, ePM10 or ISO Coarse, and carries a percentage, for example ISO ePM1 70%. BSI lists BS EN ISO 16890-1 as current. Filters are one of the parts that decide how an air handling unit performs. The air handling units page covers the units, and the AHU explainer gives the basics.

Eurovent describes three fine-particle groups, called ePMx, plus one coarse group. The "x" is the upper particle size, so each group is judged on particles from 0.3 micron up to 1, 2.5 or 10 micron. The percentage is the share removed: ISO ePM1 80% removes 80% of PM1 particles.

GroupJudged on particlesWhere published sources place it
ISO Coarse10 micron or largerA coarse prefilter ahead of the final filter
ePM100.3 to 10 micronIn polluted or city locations, a pre-filter only
ePM2.50.3 to 2.5 micronIn polluted or city locations, a pre-filter only
ePM10.3 to 1 micronRecommended for supply air in city buildings

CIBSE Journal adds that a filter must reach at least 50% to qualify for ePM1 or ePM2.5, and that a label carries only one classification. ISO also warns that its results cannot by themselves predict performance in service, so a class on a data sheet is a laboratory result, not a measure of how the filter will behave on your intake air.

What happened to G4, M5 and F7?

They belonged to EN 779:2012, which BSI shows as withdrawn on 11 July 2018. It tested filters against a fine aerosol across 0.2 to 3.0 micron and applied to filters with an initial efficiency below 98% for 0.4 micron particles. ISO 16890 measures against PM1, PM2.5 and PM10 across 0.3 to 10 micron.

So an old-to-new table is only a rough guide. On publishing its selection guide in 2017, the chair of Eurovent's air filters group said that classes rated under the two standards cannot be directly compared or converted by means of any calculation method. Eurovent compared them using real test data on the same filters, and its Eurovent 4/23 guide is now in its fourth edition (2022). CIBSE says the same in a note on its fan coil memorandum: the new classes are based on expanded tests and there is no 1-to-1 relationship with the EN 779-based classes.

  • A data sheet quoting only G4 or F7 predates the change. Ask for the ISO 16890 label and the test report behind it.
  • The old rule of thumb, as CIBSE Journal describes it, was a G4 panel prefilter followed by an F7 bag filter. Treat it as a starting point, not a specification.
  • Eurovent's certification scheme covers ISO ePM1, ePM2.5 and ePM10 filters, and excludes ISO Coarse.

Which filter class suits which building?

None is correct everywhere. CIBSE Journal says Eurovent 4/23 advises on filtration levels based on outdoor pollution and the use of the building. Its tables are Eurovent's, so they are not reproduced here.

SettingWhat decides the classWhat the sources say
Office supply airOutdoor air quality at the intake and the supply air wantedMost units have a coarse prefilter then a final filter. Selection has rarely been driven by outside air conditions, CIBSE Journal says
City-centre or main-road intakesLocal particulate levels, which vary over short distancesHSE says air expected to be heavily contaminated by traffic or smoke should be filtered. See ventilation in air quality management areas
HealthcareThe space served, set out in HTM 03-01Part A applies to new installations and major refurbishments and is the standard to be achieved. Its grades are not reproduced here. See healthcare ventilation
Server and comms roomsThe equipment makers' air cleanliness limits and the fresh-air pathNone of the sources checked names a class, so none is given. See server room cooling requirements

What does filter pressure drop do to fan energy?

A filter adds resistance, and the fan overcomes it for as long as the unit runs. CIBSE Journal calls resistance to airflow, and its effect on specific fan power, an often overlooked part of building energy use. Resistance also rises as the filter loads, so a filter with low dust-holding capacity costs more to run than its class suggests. Eurovent 4/21 grades filters by annual energy consumption, from A+ (top 5% for efficiency) to E (bottom 50%), and the ecodesign regulation for ventilation units requires makers to declare their filters' energy performance, preferably as an energy class.

The arithmetic is simple. Fan power in watts is airflow in cubic metres per second multiplied by pressure in pascals, divided by overall fan efficiency. As an illustration with assumed figures, not measured ones: a unit moving 5 cubic metres per second at 60% overall efficiency draws about 417 watts for every extra 50 pascals of filter resistance. Over 4,000 operating hours that is about 1,667 kilowatt hours a year. Multiply by your own tariff for the cost.

So a finer class is not automatically better. CIBSE Journal notes that correctly selected multi-pocket bag or compact mini-pleat filters offer more surface area, so a higher grade can be used without necessarily raising pressure drop, and says to consult the filter and fan manufacturers first. Fan type matters as well, and the EC fan retrofit guide covers the other half.

When should HVAC filters be changed?

When they reach the manufacturer's final pressure drop, not at a fixed date alone. CIBSE says filter maintenance can be based on time intervals or on condition, and that filter life depends on the contaminants, the filter's efficiency, its dust-holding capacity and the face velocity.

The ecodesign regulation builds this in for new equipment. From 1 January 2018, a non-residential ventilation unit with a filter must have a visual signal or an alarm in the control system that activates when the filter pressure drop exceeds the maximum allowable final pressure drop. Makers must also give text on the importance of regular filter changes. The regulation covers products placed on the market, so an older unit may have no alarm.

  1. Record the clean-filter pressure drop at commissioning.
  2. Take the final pressure drop from the filter data sheet and set the alarm or gauge mark at it.
  3. Log readings at each service so the loading rate is visible.
  4. Keep a calendar date as a backstop, because a sensor can fail.

HSE's advice is to make sure mechanical ventilation is maintained in line with manufacturers' instructions. The full routine is on the AHU maintenance checklist.

Where do HEPA filters fit?

Above this system. ISO 16890 covers filter elements with an ePM1 efficiency of 99% or less, and higher-efficiency elements are evaluated by other test methods, the ISO 29463 series. NHS England describes HEPA filters as at least 99.95% (H13) or 99.995% (H14) efficient at the most penetrating particle size. Cleanroom filtration is specialist design work. Readers weighing filter upgrades alongside unit replacement can send an enquiry through the site's form, with their air handling unit details to hand.

Sources

Common questions

Is a G4 or F7 grade still valid?

The standard behind those grades, EN 779:2012, was withdrawn by BSI on 11 July 2018, and new filters are classified under ISO 16890. Old filters may still be installed, but a new specification should ask for the ISO 16890 class and its test report.

Does a finer filter always give better air?

Not by itself. ISO says laboratory results cannot by themselves predict performance in service, and a finer filter usually adds resistance the fan must overcome. Choose the class the outdoor air and the building's use justify, then check the fan and filter housing can handle it.

Does my air handling unit need a filter alarm?

The ecodesign regulation requires a visual signal or alarm on non-residential ventilation units with a filter, applying to products placed on the market from 1 January 2018. An older unit may have neither. A competent contractor can add a pressure gauge or sensor, set from the filter data sheet.

Can finer filters be fitted to an existing unit?

Sometimes. CIBSE Journal says some higher-grade bag and mini-pleat filters can often be a straight swap without more pressure drop, but advises consulting the filter and fan manufacturers first. The fan duty, filter frame and housing depth all have to suit.

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