ISO 16890 is the international test and classification system for air filters used in general ventilation. It relates filter performance to PM1, PM2.5 and PM10, giving designers and buyers a more application-oriented way to compare products. However, an ePM value is not a direct measurement of how much real PM2.5 a filter will remove in a particular building.
How is an ePM rating calculated?
How is an ePM rating calculated?
The laboratory first measures fractional efficiency across a range of particle sizes. The result is an efficiency curve, not a single value at 0.3 µm. The standard then weights that curve against defined reference particle-size distributions to calculate ePM1, ePM2.5 or ePM10 efficiency. The classification process considers both initial performance and performance after the specified conditioning procedure.
For this reason, ISO ePM2.5 65% means that the filter achieved a calculated classification value under standardized laboratory conditions. It does not guarantee 65% removal of PM2.5 in every installation. Actual performance also depends on the outdoor aerosol distribution, airflow, filter loading, installation quality and bypass leakage.
What do the four groups mean?
What do the four groups mean?
- ISO ePM1 focuses on performance against the finer particle range and is often specified where indoor air quality requirements are higher.
- ISO ePM2.5 compares filters intended to reduce fine-particle exposure, but the rating remains a standardized calculated value.
- ISO ePM10 describes performance across a broader, coarser particle range.
- ISO Coarse applies to filters below the ePM10 group threshold. These filters are commonly used as prefilters to protect downstream stages.
Conditioning and dust loading are different tests
Conditioning and dust loading are different tests
The conditioning procedure in ISO 16890-4 reduces the influence of removable electrostatic charge so that the prescribed minimum fractional efficiency can be evaluated. It is not a complete simulation of months of service, humidity changes, oil mist or vibration. Dust loading under ISO 16890-3 records changes in gravimetric efficiency and resistance as test dust is captured. Those results support product comparison, but they do not form part of the final ePM classification and cannot independently predict service life.
How should buyers use ePM ratings?
How should buyers use ePM ratings?
Start with the target contaminant, outdoor air quality and system requirements, then select the appropriate ePM group. Within that group, compare efficiency, rated airflow, initial pressure drop and resistance growth. Once a filter is in the HEPA or ULPA range, ISO 29463 or EN 1822 classification and leak-testing methods are more appropriate than ISO 16890.
For manufacturers, the value of a complete test is not simply a better label. It reveals how media, filter construction and electrostatic effects combine. Customers can make a sound decision only when classification, resistance and dust-loading information are presented with the correct limitations.
