EPA / Sub-HEPA Filter Selection Guide

If you have read a cleanroom or AHU specification and seen “EPA filter” or “sub-HEPA filter” on the ductwork schedule, this guide is for you. It explains what those terms mean under EN 1822, when an E10–E12 filter is the right choice, when the project genuinely needs HEPA (H13/H14), and how the two common sub-HEPA constructions — close-pleated panel and W-type high-airflow — fit different positions in the system.

First, What “EPA” Means Here

In air filtration, EPA stands for Efficient Particulate Air, the name EN 1822 gives to Group E filter classes. It has nothing to do with the United States Environmental Protection Agency, and it is not the same as the MERV scale used for general-ventilation HVAC filters in North America (including commercial and residential systems). When a European or international cleanroom document says “EPA filter,” it almost always means an EN 1822 Group E filter — E10, E11 or E12 — whose minimum integral efficiencies at the MPPS (most penetrating particle size) are 85%, 95% and 99.5% respectively.

MERV ratings report particle-removal efficiency by particle-size range for general ventilation filters; they are not a dust-holding grade and are not limited to residential use. EN 1822 classes describe fractional efficiency at the particle size that is hardest to capture. The two scales answer different questions, and they do not convert neatly. For procurement, always work from the EN 1822 class written in the specification, not from a MERV comparison chart.

ULPA classes (U15 and above) sit above HEPA and are outside the scope of this guide; see the PTFE HEPA filter page for the high-efficiency end of the range.

For the full EN 1822 / ISO 29463 class mapping and how each filter group is tested, see What Are EPA Filters? EN 1822, ISO 29463.

EN 1822 Classes: E10–E12 vs H13–H14

EN 1822 classifies high-efficiency filters into three groups — E (EPA), H (HEPA) and U (ULPA) — with different test philosophies. This guide compares Groups E and H. Group E (EPA) is classified on integral efficiency across the whole filter, with statistical sampling accepted for classification. Group H (HEPA) adds an individual leak test and a local efficiency requirement, so every H13/H14 filter is checked for point leaks, not just average performance.

Group	Class	Integral efficiency (MPPS)	Local efficiency
EPA	E10	≥ 85%	not required for Group E
EPA	E11	≥ 95%	not required for Group E
EPA	E12	≥ 99.5%	not required for Group E
HEPA	H13	≥ 99.95%	≥ 99.75%
HEPA	H14	≥ 99.995%	≥ 99.975%

Two practical conclusions follow. First, the penetration allowed at the MPPS drops by about a factor of ten from E12 to H13 — moving up a class is a significant change, not a marginal one. Second, the difference between the groups is as much about testing rigor as about the number. HEPA duty carries a per-filter evidence trail; EPA duty normally does not.

When EPA (E10–E12) Is Enough

Intermediate stage after medium-efficiency filtration

The classic position for a sub-HEPA filter is between the medium-efficiency stage and the terminal HEPA stage. Medium-efficiency filters (F5–F9 to EN 779, in synthetic or glass fibre, panel and box constructions) protect the downstream fine filters and handle the bulk of the particulate load. An EPA filter downstream of that stage polishes the air further — capturing fine fraction particles that pass the middle stage — before air reaches terminal HEPA filters or is supplied to medium-to-high cleanliness zones. In this duty the EPA filter extends terminal HEPA life rather than providing the final barrier, so the per-filter leak-test discipline of Group H is usually unnecessary.

Specifications that name E11 or E12

Some pharmaceutical, electronics, food and cosmetics specifications name E11 or E12 explicitly for make-up air, recirculation or AHU final stages. If the spec sheet says E11, quote E11: upgrading to E12 or H13 without being asked may add cost and may raise resistance depending on media, pack area and rated airflow, which can shift the fan’s operating point. Confirm the pressure drop of the quoted configuration against the available fan pressure before changing class.

AHU sections where airflow and fan pressure dominate

In central air handling, the constraint is often available fan pressure and the physical depth of the filter section, not leak-tightness. Here the buyer’s real questions are rated airflow at acceptable initial resistance, frame compatibility with the holding frame or slide rail, and seal geometry to limit bypass. That is exactly the territory of sub-HEPA (EPA) panel filters and W-type high-airflow filters, both built for cleanrooms and areas between medium and HEPA stages.

When You Need HEPA Instead

Terminal cleanroom, FFU and supply outlet duty

Whenever the filter is the final barrier before the cleanroom — ceiling terminal housings, FFU (fan filter unit) arrays, unidirectional supply outlets, isolation and barrier applications — the efficiency and integrity requirements jump. This is H13/H14 territory. For terminal duty, look at mini-pleat HEPA filters (separatorless mini-pleat construction of ultra-fine glass fibre paper with hot-melt pleat spacing; a published example row is 610 × 610 × 69 mm, H13, at 1,000 m³/h with 175 Pa initial resistance) or gel-seal HEPA filters where a knife-edge gel seal is needed for ceiling integrity (a published example is 636 × 636 × 69 mm, H14, at 1,000 m³/h with 190 Pa initial resistance). These figures are published reference examples, confirmed per configuration on the quotation.

Protocols that require individual leak testing

If the validation or quality protocol calls for per-filter leak test evidence with serial-number traceability — standard practice in H13/H14 supply, as covered in our HEPA replacement checklist — then Group H is the requirement, and an EPA filter cannot substitute. Under EN 1822, Group H classification includes an individual leak test and a local efficiency value; Group E classification relies on integral efficiency with statistical sampling. Do not accept a batch certificate where the protocol expects per-filter evidence, and do not pay for per-filter evidence where a classification certificate is all the duty needs.

The dividing question is simple: is this filter the final barrier that the cleanroom validation relies on? If yes, specify H13/H14. If it protects or pre-filters that barrier, E10–E12 is usually enough.

Panel Sub-HEPA vs W-Type High-Airflow Sub-HEPA

Both constructions serve the between-medium-and-HEPA position, but they fit different installation types.

Panel close-pleat sub-HEPA

Sub-HEPA (EPA) filters are close-pleated panel filters on ultra-fine glass fibre or polypropylene paper. Close pleating packs a large media area into the frame size, which keeps operating resistance low, and the sealed frame construction limits bypass leakage around the pack. They suit holding frames between the medium-efficiency and terminal HEPA stages 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 are all listed application areas for this construction. Panel format is the default choice where the filter sits in a standard holding frame or housing at moderate depth.

W-type high-airflow sub-HEPA

W-type high-airflow filters use a W-profile pack to deliver high airflow capacity at moderate initial resistance, in a compact footprint, on glass fibre paper or ultra-fine polypropylene paper media. Source catalogue constructions include thin-panel, separator-frame and wedge designs. They are aimed at central air conditioning and central ventilation systems — pharmaceutical plants, biological laboratories, hospital operating rooms, food production and cosmetics manufacturing — where the filter section must move large volumes without excessive fan pressure. One option worth flagging in your RFQ: polypropylene media versions are incinerable after use, which simplifies disposal where incineration is the approved route.

SENPEI supplies both constructions in confirmed size, depth, frame and class, with the matching gasket or seal position. Installation, in-situ leak testing and final air balancing remain with the buyer. Both products are quotation on request — detailed technical parameters are confirmed for the requested configuration rather than taken from a published table.

Selection Checklist Before You Enquire

Work through this list before sending an RFQ; it mirrors the inputs the product pages ask for.

Position in the system: middle-stage pre-filter, intermediate EPA stage, or terminal barrier. This decides Group E vs Group H.
Required class: the EN 1822 class written in the specification (E10, E11, E12, H13 or H14) — quote the class, not an approximation.
Frame size and installation: W×H×D in mm, plus the holding frame, housing, filter section or slide rail the filter must fit.
Rated airflow and allowable resistance: what the fan and filter section can support, and any initial or final pressure-drop limits in the spec.
Frame material and sealing method: including gasket or seal position, and whether bypass control is critical at this stage.
Media type: glass fibre or polypropylene; for W-type, state any incineration requirement so the polypropylene option can be quoted.
Quantity and replacement cycle: how many filters, expected replacement frequency, and destination country or port for logistics planning.
Documentation: what test evidence the project protocol expects — classification data or per-filter test records.

Documentation and Testing Expectations

Match the paperwork to the group. For EPA filters, EN 1822 Group E classification is based on integral efficiency, with statistical sampling accepted for classification — so batch-level or classification documentation is normal, and it is reasonable to confirm the delivery format on the quotation. For HEPA filters, site practice is per-filter test evidence with serial-number traceability, as described in the HEPA replacement checklist. Also confirm practical delivery items with the supplier: labeling, packing, and whether any in-situ testing support is included or stays with the buyer — for SENPEI supply, installation, in-situ leak testing and final balancing stay with the buyer.

What a Complete Request Looks Like

A complete RFQ lets the supplier quote the correct construction first time. Two examples:

Panel sub-HEPA (EPA), intermediate stage:

Application: intermediate filtration between F-class medium stage and terminal HEPA
Filter: close-pleat sub-HEPA panel filter, [E11 or E12] to EN 1822
Frame size: [W×H×D mm], holding frame type [type/housing reference]
Frame material and sealing method: [material], gasket/seal position [position]
Rated airflow: [rated airflow] m³/h at [allowable initial resistance] Pa
Documentation delivery: [classification certificate / other — confirm format on quotation]
Quantity: [quantity], replacement cycle [expected cycle]
Destination: [country or port]

W-type high-airflow sub-HEPA, central AHU:

Application: central air conditioning filter section, high airflow / low resistance
Filter: W-type high-airflow sub-HEPA filter, [E10–E12] to EN 1822
Casing size: [W×H×D mm], filter section / slide rail reference [reference]
Construction: [thin-panel / separator-frame / wedge]
Media: [glass fibre / polypropylene], incineration required: [yes/no]
Rated airflow: [rated airflow] m³/h at [allowable initial resistance] Pa
Documentation delivery: [classification certificate / other — confirm format on quotation]
Quantity: [quantity]
Destination: [country or port]

Fill the brackets from the specification and the site survey. If a value is not fixed yet — say the frame depth depends on the existing housing — state that explicitly and ask the supplier to confirm options on the quotation.

Selected official references

Next Steps

Browse the full air filter range to compare constructions, then request a quote with your frame size, class, airflow and quantity for confirmation against the requested configuration.

All product parameters are reference values and are confirmed on the quotation.