In a cleanroom specification, EPA means EN 1822 classes E10–E12 (Efficient Particulate Air, also called sub-HEPA). It is not the US Environmental Protection Agency (epa.gov), not a household room-air filter, and not a water filter.
When a specification calls for an “EPA filter”, it is not using a brand name or a loose marketing label. It means a Group E filter as defined by EN 1822-1 or ISO 29463-1 — an efficient particulate air filter, also commonly referred to as a sub-HEPA filter. The name is EN 1822 classes E10–E12, not epa.gov, a household room-air filter, or a water filter.
This article explains what an EPA filter is, how the EN 1822 and ISO 29463 classification systems define the E, H and U groups, how EPA filters are tested differently from HEPA filters, and where an EPA stage sits in a cleanroom air-handling system. If your question is instead “which class and construction do I need for this project”, see our EPA / sub-HEPA filter selection guide.
What an EPA filter is
EN 1822-1 and ISO 29463-1 divide high-efficiency filters into three groups:
- Group E — EPA (Efficient Particulate Air) filters. ISO 29463-1 notes that Group E filters are “also commonly referred to as sub-HEPA”.
- Group H — HEPA (High Efficiency Particulate Air) filters.
- Group U — ULPA (Ultra Low Penetration Air) filters.
All classes in all three groups are defined by efficiency at the MPPS — the most penetrating particle size. The MPPS is the particle size at which a given filter’s efficiency is lowest, and it is typically in the range of about 0.1–0.3 µm, depending on the medium and air velocity. Because a filter is easiest to penetrate at its MPPS, the standards grade it at that worst-case size rather than at a single fixed particle size.
Two standards, one structure: EN 1822 and ISO 29463
EN 1822 is the original European classification series; ISO 29463 is the international series built on it, and it follows the same structure. Both EN 1822-1:2019 and ISO 29463-1 classify filters into three groups — E, H and U — by efficiency at the MPPS.
EN 1822 labels its classes E10, E11, E12, H13, H14, U15, U16 and U17. ISO 29463 instead names its classes from ISO 05 E up to ISO 75 U. ISO 29463-1:2024, the third edition published in August 2024, replaced the 2017 edition; one of the listed changes is that two E classes were added. That is why the ISO Group E range now runs from ISO 05 E to ISO 30 E, while the EN 1822 Group E keeps its three classes, E10 to E12.
The ISO names are easy to read once you know the pattern. From ISO 10 E upward, the first digit of the class number gives the count of leading nines in the minimum overall efficiency, and a second digit of 5 adds a trailing 5: ISO 20 E is 99%, ISO 25 E is 99.5%, ISO 35 H is 99.95% and ISO 45 H is 99.995%. ISO 05 E (85%) is the exception. Treat this only as a reading aid; the published threshold tables are the authoritative figures.
EN 1822 vs ISO 29463 class mapping
The table below maps the two systems side by side. All values are minimums at the MPPS. The local column applies only to Group H and Group U filters; Group E filters are not leak tested and have no local requirement.
| EN 1822 class | ISO 29463 class | Group | Minimum overall (integral) efficiency | Minimum local efficiency |
|---|---|---|---|---|
| E10 | ISO 05 E | EPA | 85% | — (not leak tested) |
| — | ISO 10 E | EPA | 90% | — |
| E11 | ISO 15 E | EPA | 95% | — |
| — | ISO 20 E | EPA | 99% | — |
| E12 | ISO 25 E | EPA | 99.5% | — |
| — | ISO 30 E | EPA | 99.9% | — |
| H13 | ISO 35 H | HEPA | 99.95% | 99.75% |
| — | ISO 40 H | HEPA | 99.99% | 99.95% |
| H14 | ISO 45 H | HEPA | 99.995% | 99.975% |
| — | ISO 50 U | ULPA | 99.999% | 99.995% |
| U15 | ISO 55 U | ULPA | 99.9995% | 99.9975% |
| — | ISO 60 U | ULPA | 99.9999% | 99.9995% |
| U16 | ISO 65 U | ULPA | 99.99995% | 99.99975% |
| — | ISO 70 U | ULPA | 99.99999% | 99.9999% |
| U17 | ISO 75 U | ULPA | 99.999995% | 99.9999% |
Rows that appear on the same line share the same minimum threshold, but EN 1822 and ISO 29463 remain separate documents, and the labels are not interchangeable. A specification should state which standard and which class it means: “E12 to EN 1822-1” and “ISO 25 E to ISO 29463-1” share the same minimum threshold but refer to different documents, while “EPA, 99.5%” written without naming a standard leaves the test basis open. And because the values are minimums rather than ranges, meeting a class means reaching or exceeding the figure shown.
The local values for Group H apply to the reference MPPS particle-scanning leak test. Footnote d to Tables 1 and 2 of ISO 29463-1:2024 notes that alternate limits may be specified when photometer or oil-thread leak testing is used, so do not carry the local figures across to a different leak-test method without checking the test basis.
How EPA filters are tested — and why it differs from HEPA
Finding the MPPS
Testing starts with the medium. The MPPS is determined first on flat-sheet filter media under ISO 29463-3 (adopted in Europe as EN ISO 29463-3, which EN 1822-1:2019 references; it replaced the older EN 1822-3), and finished filter elements are then tested at their nominal airflow using that particle size. The particle size used for classification is therefore the one that challenges the filter most, matched to the medium and operating point rather than picked as a generic constant.
Integral vs local efficiency
Two kinds of efficiency value are reported. The integral, or overall, value describes the efficiency of the whole filter element. The local value describes the efficiency at any single point on the filter face and is used to find localised leaks. Only Group H and Group U filters carry local efficiency limits. For elements, EN 1822 also requires the pressure difference to be recorded at the nominal airflow — a class value is only meaningful together with the airflow at which it was measured.
Statistical sampling for Group E, individual testing for H and U
The three groups follow different test regimes:
- Group E: efficiency is determined by statistical sample testing — ISO 29463-1 says “statistical sample testing only”. For classification purposes, Group E filters “cannot and shall not be leak tested”. An E-class label therefore classifies the production type or batch, not an individually scanned filter.
- Group H: every filter is individually leak tested, and integral efficiency is normally determined on each filter at the MPPS. The two standards allow different methods:
- ISO 29463-1: leak testing follows ISO 29463-4 with the reference scan method; alternate methods, including photometer and oil-thread methods, are permitted and should be identified on the filter and on the certificates.
- EN 1822-1:2019 (§7.4.3–7.4.4): Group H filters are leak tested by the reference scanning method or the oil-thread test (EN ISO 29463-4, Annex A), and H13 may also be tested to Annex F of that standard. The aerosol photometer scan leak test is not allowed. For filters leak tested by the Annex A oil-thread method, integral efficiency may be determined on a statistical basis rather than on each filter — every filter is still leak tested.
- Group U: every filter is tested individually and leak tested by the scan method only; no alternate leak-test method is allowed.
The practical takeaway is simple: an E-class label is a type or batch classification, not an individual leak certificate. If a project needs per-filter leak evidence, it needs a Group H filter — our HEPA replacement checklist explains what to look for on the label and certificates.
Where EPA filters sit in a cleanroom air system
A cleanroom air train is normally staged from coarse to fine: a coarse or pre-filter stage removes the bulk of the particle load, a medium-efficiency stage takes out the finer fraction, an EPA (sub-HEPA) stage polishes the air further, and terminal HEPA — or ULPA in the most demanding rooms — sits at the point of supply. Terminal cleanroom ceilings, fan filter units (FFUs) and supply outlets normally use HEPA filters.
The EPA stage earns its place in two ways. Upstream of the terminal filters, it removes particles that would otherwise load the HEPA or ULPA stage, protecting that investment and extending its service life. And in zones whose specification calls for an E class as the final stage, the EPA filter serves as the final filter itself.
SENPEI supplies the stages around the EPA position: coarse filters and pre-filters for the first stage, medium-efficiency filters (F5–F9 to EN 779) for the middle stage, sub-HEPA (EPA) panel filters and W-type high-airflow sub-HEPA filters for the EPA stage, and mini-pleat HEPA filters and PTFE membrane HEPA and ULPA panels for terminal filtration.
Typical applications for EPA filters
EPA-class filters are typically used where the air needs to be cleaner than a medium-efficiency stage can deliver but a HEPA terminal stage is not called for, or upstream of a terminal stage to protect it. Typical applications include:
- Intermediate and terminal filtration in cleanrooms and laboratories
- Semiconductor, precision electronics and instrument manufacturing
- Pharmaceutical production, hospital areas and operating rooms
- Food processing, automotive painting and nuclear research facilities
- Central air-conditioning and central ventilation systems serving pharmaceutical plants, biological laboratories, hospital operating rooms, food production areas and cosmetics manufacturing — the typical duty for W-type high-airflow sub-HEPA filters, which are available with glass fibre or ultra-fine polypropylene paper media, the polypropylene versions being incinerable after use
These are typical uses rather than guarantees of suitability: the class and configuration must always follow the zone specification.
Choosing an EPA class (brief)
A few starting points before the detailed selection work:
- Start from the zone specification, which should name the standard (EN 1822 or ISO 29463) and the class required.
- Remember that EN 1822 Group E covers E10–E12 (same thresholds as ISO 05 E, ISO 15 E and ISO 25 E); ISO 29463 also has ISO 10 E, ISO 20 E and ISO 30 E, which have no EN 1822 equivalent.
- Match the construction to the plant: close-pleated panels for holding frames between the medium and HEPA stages, W-type high-airflow filters for central air-conditioning and ventilation.
- SENPEI publishes no fixed numeric table for its EPA range; parameters are confirmed per configuration on the quotation.
The full checklist — including when E10–E12 is enough versus HEPA, and the documentation and RFQ templates — is in the EPA / sub-HEPA filter selection guide.
Selected official references
- ISO 29463-1:2024 — High-efficiency filters and filter media for removing particles in air
- BS EN 1822-1:2019 — High efficiency air filters (EPA, HEPA and ULPA): Classification, performance testing, marking
Questions buyers ask
What does "EPA filter" mean in a cleanroom specification?
In this cleanroom context, EPA means Efficient Particulate Air: EN 1822 Group E classes E10, E11 and E12, also commonly called sub-HEPA. It is not the US Environmental Protection Agency (epa.gov), not a household room-air filter, and not a water filter. The class is defined by EN 1822-1 or ISO 29463-1, not by a brand name or a marketing label.
How do EPA filters differ from HEPA filters?
EN 1822 and ISO 29463-1 divide high-efficiency filters into Group E (EPA), Group H (HEPA) and Group U (ULPA). EN 1822 Group E is E10–E12; HEPA starts at H13. Group E filters are classified by statistical sample testing and shall not be leak tested; an E-class label classifies the production type or batch. Group H filters are individually leak tested. If a project needs per-filter leak evidence, it needs a Group H filter.
How do EN 1822 and ISO 29463 name EPA classes?
EN 1822 labels Group E as E10, E11 and E12. ISO 29463 names Group E from ISO 05 E to ISO 30 E. Some rows share the same minimum MPPS threshold, but the documents and labels are not interchangeable. A specification should state which standard and which class it means.
Where does an EPA stage sit in a cleanroom air system?
A cleanroom air train is normally staged from coarse to fine. An EPA (sub-HEPA) stage typically sits after medium-efficiency filtration and before terminal HEPA or ULPA, to protect the terminal stage, or it can be the final filter where an E class is specified. Terminal cleanroom ceilings, fan filter units and supply outlets normally use HEPA filters.
What should I confirm before requesting a quotation?
Start from the zone specification, which should name the standard (EN 1822 or ISO 29463) and the class required. Match the construction to the plant: close-pleated panels for holding frames between the medium and HEPA stages, or W-type high-airflow filters for central air-conditioning and ventilation. SENPEI publishes no fixed numeric table for its EPA range; parameters are confirmed per configuration on the quotation.
Need an EPA (E10–E12) stage quoted?
Share the zone standard/class, holding frame or W-type construction, quantity and destination. Parameters are confirmed per configuration on the quotation.
Related reading
Product parameters are confirmed for each configuration on the quotation; standards values above are the published minimums of EN 1822-1:2019 and ISO 29463-1:2024.