What Do Filter Classes Mean? ISO 16890, F7, M5 and EPA Explained

Indoor air quality has a significant impact on people's health, comfort, and the energy efficiency of buildings. One of the most important components of any ventilation system is the air filter, whose purpose is to remove dust, pollen, fine particles, and other contaminants from the air. When selecting filters, you may come across classifications such as F7, M5, ePM1, ePM10, or EPA. But what do these filter classes actually mean, and how are they related?

In this article, we explain the most common filter classifications and the differences between the former EN 779 standard and the current ISO 16890 standard.

Why Is Filter Classification Important?

A filter classification indicates how effectively a filter can remove particles of different sizes from the air. Choosing the right filter affects:

• Indoor air quality

• Ventilation system performance

• Energy efficiency

• Occupant health and wellbeing

• The lifespan of equipment and ductwork

Modern buildings increasingly require filters that can effectively capture fine particles that may be harmful to human health.

The Former Filter Classification System: EN 779 and the G, M, and F Classes

For many years, the EN 779 standard was used throughout Europe. Under this system, filters were divided into three main categories:

G-Class Filters

G-class filters (G1–G4) remove the largest dust and dirt particles.

Typical applications include:

• Pre-filtration

• Industrial ventilation systems

• Equipment protection

Under ISO 16890, these filters generally correspond to the Coarse filter category.

M-Class Filters

M-class filters (M5 and M6) are medium-efficiency filters.

Their purpose is to remove:

• Finer dust particles

• Pollen

• Other medium-sized airborne particles

M5 filters are often used as pre-filters before higher-efficiency fine filters.

F-Class Filters

F-class filters (F7–F9) are known as fine filters.

They effectively remove:

• Road dust

• Pollen

• Combustion particles

• A portion of fine particulate matter

In particular, the F7 filter was one of the most commonly used ventilation filter classes in offices, schools, and residential buildings for many years.

ISO 16890 – The Current International Standard

In 2018, EN 779 was replaced by the ISO 16890 standard, which provides a more accurate representation of filter performance.

Previously, filters were tested using specific particle sizes under laboratory conditions. ISO 16890, however, is based on particle sizes that are commonly found in real-world outdoor air.

Under this standard, filters are classified according to their efficiency in removing:

• PM1 particles (smaller than 1 micrometer)

• PM2.5 particles (smaller than 2.5 micrometers)

• PM10 particles (smaller than 10 micrometers)

PM stands for Particulate Matter.

What Do ePM1, ePM2.5, and ePM10 Mean?

Under ISO 16890, filter performance is expressed as a percentage efficiency rating.

ePM1 70%

The filter removes an average of 70% of particles smaller than 1 micrometer.

These include:

• Traffic-related fine particles

• Combustion particles

• Some of the most harmful airborne pollutants

ePM2.5 65%

The filter removes approximately 65% of particles smaller than 2.5 micrometers.

Examples include:

• Fine dust

• Certain smoke particles

• Air pollution particles

ePM10 80%

The filter removes approximately 80% of particles smaller than 10 micrometers.

These include:

• Pollen

• Construction dust

• Larger respirable particles

How Does F7 Compare to ISO 16890?

This is one of the most common questions when replacing ventilation filters.

There is no exact equivalent to the old F7 classification because the testing methods differ. However, in most cases, an F7 filter corresponds approximately to:

ePM1 50–70%

The exact equivalence depends on the manufacturer and filter design.

For this reason, F7 classifications should not be directly compared with a single ISO 16890 class without consulting the manufacturer's technical specifications.

What Are EPA Filters?

EPA filters belong to a higher-performance category than standard ventilation fine filters.

EPA stands for:

Efficient Particulate Air

According to the EN 1822 standard, EPA filters are classified as:

• EPA E10

• EPA E11

• EPA E12

These filters are highly effective at removing very small particles and aerosols.

Typical applications include:

• Hospitals

• Laboratories

• Cleanrooms

• Food processing facilities

• Electronics manufacturing environments

EPA filters offer a performance level between conventional ventilation filters and HEPA filters.

How to Choose the Right Filter

The best filter depends on the application.

Residential Buildings

Typical recommendations include:

• An ePM1-class supply air filter

• A Coarse-class exhaust air filter

This combination helps maintain good indoor air quality while supporting energy efficiency.

Offices and Public Buildings

Commonly used filters include:

• ePM1 50–70%

• ePM2.5-class filters

These filters effectively reduce fine particles originating from outdoor air pollution.

Special Applications

Hospitals, laboratories, and cleanrooms often require:

• EPA filters

• HEPA filters

• Multiple filtration stages

to achieve the necessary air cleanliness levels.