Classification of Air Filters

Air filter classification is regulated by a series of very strict standards that specifically define the features of the filters according to the relevant efficiency class and use.

The air filters considered by the standards belong to threee main groups:

  • coarse
  • fine
  • absolute

The absolute filters are divided into two different classes:

  • HEPA (High Efficiency Particulate Air Filters)
  • ULPA (Ultra Low Penetration Air Filters)

EN 779-2009 Standard

This standard aims to determine the arrestance of coarse filters with synthetic dust by using a gravimetric method and the efficiency of fine filters by using a particle counter method.The standard has a double classification system that uses letters and numbers: G and F respectively for coarse and fine filters, followed by numbers from 1 to 9 as shown below.

Classification of coarse and fine filters according to EN 779 and EU 4/5
Type of filterEN 779Avg. arrestance withAvg. opacimetricFinal pressure dropClass Eurovent 4/9*
synthetic dustsefficiencyPa
CoarseG1Am < 65250EU 1
G265 < Am < 80250EU 2
G380 < Am < 90250EU 3
G490 < Am250EU 4
FineF540 < Em < 60450EU 5
F660 < Em < 80450EU 6
F780 < Em < 90450EU 7
F890 < Em < 95450EU 8
F995 < Em450EU 9

Am = Average arrestance referred to the Weight/Gravimetric method

Em = Average efficiency referred to the Colorimetric/Opacimetric method

* According to the EUROVENT 4/5 classification that does not specify the final pressure drop.

EN 1822 Standard

The most recent standard concerning HEPA and ULPA air filters is EN 1822:2009

The new standard is composed of 5 parts, each dealing with one specific subject which is described in detail.

It was stated that any single filtering medium has a point of maximum penetration (or lowest efficiency) according to a specific particle size which is variable according to air flow speed, media density and the diameter of the medium fibre.

It was then established that each filter certification ought to be based on the MPPS (Most Penetrating Particle Size) which is the most critical.

The standard classifies the HEPA (High Efficiency Particulate Air Filters) and ULPA (Ultra Low Penetration Air Filters) filters separately: the first from E10 to H14 and the second from class U15 to U17.

The test consists of a double control, the first is carried out on the media and measures the size of the most penetrating particle (MPPS) verifying that the speed across the medium is the same as during the actual operation. The second control is carried out on the finished product and determines the global MPPS efficiency.

Filters with a global efficiency over 99.5% are to undergo an additional test on each point of their filtration surface with the aim of finding out a possible leakage (pinholes)whose local penetration value should be no higher than 5 times (classes H13 – U16) and 20 times (class U17) the global one.

Classification of high and very high efficiency filters according to EN 1822 
Type of filterClass EN 1822Global MPPS % efficiencyLocal efficiency localised drop %Test methods required to be submitted individual filter elements
HEPAE1085test type (EN 1822-4/EN 1822/5)
E1195test type (EN 1822-4/EN 1822/5)
E1299.5test type (EN 1822-4/EN 1822/5)
H1399.9599.75MPPS scan method/oil thread method
H1499.99599.975MPPS scan method/oil thread method
ULPAU1599.999599.9975MPPS scan method (EN 1822-4)
U1699.9999599.99975MPPS scan method (EN 1822-4)
U1799.99999599.9999MPPS scan method (EN 1822-4)
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