If you are specifying, replacing or maintaining air filters for a ventilation or air-conditioning system, you may still come across familiar terms such as G4, F7 and F9. These classifications come from the former EN 779 standard.
Today, general ventilation filters are classified under BS EN ISO 16890, which uses a different system based on a filter's performance against particulate matter such as PM1, PM2.5 and PM10. That change has created a common question:
What is the ISO 16890 equivalent of an F7, F9 or G4 filter?
The answer is not quite as simple as matching one old filter class to one new one.
In this guide, we explain what replaced EN 779, how ISO 16890 works, why there is no exact F7 equivalent, and what UK building operators, consultants and HVAC professionals should consider when selecting filters today.
What replaced EN 779?
EN 779 was previously used to classify particulate air filters for general ventilation. It included familiar classes such as:
- G1 to G4
- M5 and M6
- F7 to F9
EN 779:2012 was withdrawn in 2018 and superseded by the ISO 16890 series, adopted in the UK as BS EN ISO 16890. Instead of classifying filters primarily using the older G, M and F system, ISO 16890 describes filter performance using particulate-matter categories.
The principal classifications are:
- ISO ePM1
- ISO ePM2.5
- ISO ePM10
- ISO Coarse
This makes it easier to understand how a filter performs against particle-size fractions that are relevant to real-world indoor and outdoor air quality.
What does ISO 16890 mean?
ISO 16890 is a testing and classification standard for particulate air filters used in general ventilation systems. It evaluates a filter's fractional efficiency across a range of particle sizes and uses those results to calculate performance against recognised particulate-matter fractions. For example, a filter might be classified as:
ISO ePM1 60%
This means it has a calculated efficiency of at least 60% against the defined PM1 fraction, subject to the test methodology, minimum efficiency requirements and rounding rules set by ISO 16890. It does not mean that the filter captures exactly 60% of every individual particle smaller than 1 micrometre.
What are PM1, PM2.5 and PM10?
PM stands for particulate matter. The number refers to the approximate aerodynamic diameter of particles in micrometres.
PM10
PM10 refers to particulate matter with an aerodynamic diameter of up to approximately 10 micrometres. These particles can enter the respiratory system and include material such as dust, pollen and other airborne particulates.
PM2.5
PM2.5 refers to much finer particles, with a diameter of up to approximately 2.5 micrometres. Because of their small size, these particles can travel deeper into the respiratory system. PM2.5 is also an important metric in UK outdoor-air-quality monitoring.
PM1
PM1 refers to even smaller particulate matter. ISO 16890 uses the PM1 fraction because very fine particles are particularly relevant when considering indoor air quality and filtration performance.
What is the difference between EN 779 and ISO 16890?
The biggest difference is the way filter efficiency is assessed and communicated.
Under EN 779, performance at a particle size of 0.4 micrometres was an important classification parameter for medium and fine filters. ISO 16890 evaluates fractional filtration efficiency over a wider particle-size range and uses this data to calculate performance against PM1, PM2.5 and PM10.
This means the newer classification system gives designers and operators information that is more directly related to airborne particulate-matter fractions. It also means that old and new filter classes cannot simply be exchanged on a one-for-one basis.
What is the ISO 16890 equivalent of an F7 filter?
There is no exact ISO 16890 equivalent of an F7 filter.
This is an important distinction.
You may find conversion charts online that suggest a typical F7 filter could correspond to a particular ePM1 or ePM2.5 range. These tables can be useful as an indicative comparison, but they should not be treated as a guaranteed technical conversion.
EN 779 and ISO 16890 use different test methods and classification criteria. Two filters previously classified as F7 could therefore receive different ISO 16890 classifications. For replacement or specification purposes, the better approach is to identify the filtration performance required by the application and select an ISO 16890 filter accordingly.
What should you replace an old EN 779 F7 filter with?
If the filter currently installed is marked EN 779 / F7, avoid simply ordering a product described as an “F7 equivalent”. First check the existing filter manufacturer and model, if available, to see whether its current ISO 16890 test data can be identified.
As an indication of the possible range, testing of filters classified as F7 under EN 779 has shown ISO 16890 performance spanning approximately ePM1 40–65%, ePM2.5 65–75% and ePM10 80–90%. This is why there is no single ISO class that can universally replace F7.
When selecting a replacement, match the required filtration performance for the application and also confirm the filter dimensions, airflow, initial pressure drop, system capacity and installation arrangement. Where the original design requirement is unclear, the replacement should be selected against the building's current indoor-air-quality and ventilation requirements rather than relying solely on the old F7 designation.
Is there a G4 equivalent under ISO 16890?
The same principle applies to former G4 filters; there is no universal direct conversion.
Many filters previously marketed as G4 may now fall within the ISO Coarse classification, but the precise performance should be confirmed from the manufacturer's current ISO 16890 test data. Under ISO 16890, filters that do not achieve the minimum ePM10 efficiency required for an ePM classification are classified as ISO Coarse.
The percentage shown with an ISO Coarse rating represents initial gravimetric arrestance rather than ePM10 efficiency.
What about F9 filters?
Again, an F9 classification should not automatically be replaced with a single assumed ISO ePM1 class. Higher-efficiency former EN 779 filters will generally correspond to stronger particulate-matter performance under ISO 16890, but the actual classification depends on the tested filter.
Where an old design specification states F9, the appropriate solution is to review the required indoor-air-quality performance and choose a current filter based on verified ISO 16890 data.
Is ISO 16890 a UK legal requirement?
ISO 16890 itself is a technical standard rather than a piece of UK legislation.
This distinction is important.
UK regulatory requirements relating to ventilation generally focus on providing suitable ventilation, maintaining appropriate indoor air quality and controlling contaminants. They do not impose one universal ISO 16890 filter class across every building and every ventilation system.
The correct filter will depend on the application.
Factors can include:
- the quality of the outdoor air
- the indoor air quality required
- building type
- occupancy
- system design
- contaminant levels
- pressure drop
- energy consumption
- maintenance requirements
- sector-specific standards and guidance
For this reason, the filtration requirements for a school, office, healthcare facility, industrial building or residential property may be very different.
Why does air filter selection matter?
Air filters perform more than one role in an HVAC system. Depending on the application, they can help:
- reduce airborne particulate matter entering occupied spaces
- support indoor air quality
- protect ventilation equipment
- reduce contamination of ductwork and system components
- maintain system cleanliness
- support specialist environmental requirements
However, selecting the highest-efficiency filter available is not always the right solution. For example, higher filtration efficiency can also be associated with greater resistance to airflow. That can affect fan performance and energy consumption if the ventilation system has not been designed for the filter being used.
Correct filter selection should therefore balance air quality, filtration efficiency, pressure drop, energy consumption and system capability.
Should you replace an F7 filter with an ISO ePM1 filter?
Possibly, but not simply because a comparison table says they are equivalent. Before changing a filter specification, consider:
- What level of indoor air quality is required?
- What pollutants are present in the outdoor air?
- What ISO 16890 performance does the replacement filter provide?
- Can the ventilation system accommodate its pressure drop?
- Are there additional sector-specific requirements?
- What was the original design intent of the system?
For existing installations, reviewing the complete filter specification is preferable to replacing an old EN 779 designation with a guessed ISO equivalent.
What should be included in a modern air filter specification?
Rather than specifying only an obsolete EN 779 class such as F7, a modern HVAC filter specification should ideally include the required ISO 16890 classification and performance.
Depending on the project, it may also be useful to specify:
- filter dimensions
- initial pressure drop
- final recommended pressure drop
- airflow rate
- construction
- filter media
- fire-performance requirements where applicable
- expected operating conditions
- energy-performance considerations
- replacement and maintenance requirements
This gives designers, contractors and maintenance teams a much clearer basis for selecting a suitable product.
EN 779 vs ISO 16890: quick summary
| EN 779 | ISO 16890 |
|---|---|
| Former general ventilation filter standard | Current general ventilation filter classification framework |
| Used G, M and F filter classes | Uses ePM1, ePM2.5, ePM10 and ISO Coarse |
| F7, F8 and F9 commonly specified | Performance expressed against particulate-matter fractions |
| 0.4 μm efficiency was an important classification parameter | Fractional efficiency is assessed across a wider particle-size range |
| Withdrawn | Current framework |
| Direct conversions often assumed | No exact one-to-one conversion should be assumed |
Frequently asked questions
Is EN 779 still valid in the UK?
EN 779:2012 has been withdrawn and should generally be regarded as a legacy classification system for general ventilation filters.
New specifications should normally refer to the relevant current BS EN ISO 16890 classification.
What replaced F7 filters?
F7 was an EN 779 classification.
There is no single universal ISO 16890 replacement for F7 because the two standards use different testing and classification methods.
The correct replacement should be selected using verified ISO 16890 performance data and the requirements of the application.
What does ePM1 60% mean?
ISO ePM1 60% indicates a calculated filtration efficiency of at least 60% against the defined PM1 particulate-matter fraction, subject to ISO 16890's test and classification rules.
Is ISO ePM1 better than ePM2.5?
Not necessarily in every application.
An ePM1 classification indicates performance against a smaller particulate-matter fraction, but filter selection should be based on the required indoor air quality and ventilation-system design rather than simply choosing the highest number available.
Is ISO Coarse the same as G4?
No.
Many former G-class filters may now be marketed within the ISO Coarse category, but ISO Coarse and G4 are based on different testing and classification methods.
They should not be treated as exact equivalents.
Do UK Building Regulations require ISO 16890 filters?
UK ventilation requirements do not generally mandate one universal ISO 16890 filter class for all buildings.
The appropriate filter specification depends on the building, system, indoor-air-quality requirements and relevant technical guidance.
The key takeaway
If your HVAC specification still refers to G4, F7, F8 or F9 filters, it is worth reviewing it.
EN 779 is now a legacy classification system, while BS EN ISO 16890 is the current framework used to classify particulate air filters for general ventilation in the UK.
The important point is not to simply replace an old EN 779 class with a supposed direct ISO equivalent. Instead, identify the filtration performance the building actually requires and select a filter using verified ISO 16890 data. This provides a more reliable basis for improving indoor air quality, protecting HVAC equipment and ensuring the ventilation system performs as intended.
Next post
MVHR Filter FAQs: Choosing, Measuring and Replacing Ventilation Filters
Updated on 28 July 2026
