Understanding HEPA Filter Classification: H13 H14 U15 and ULPA Grades

By Mike Chen, Production Director • Xiamen KWS Purification Technology Co., Ltd. • July 2026

A procurement manager from a pharmaceutical company in Shenzhen once called me and said, 'I need HEPA filters for my cleanroom'. When I asked which grade, he said, 'Just HEPA, the usual kind.' The problem is, there is no 'usual kind' of HEPA — there are at least seven distinct grades under international standards, ranging from 99.95% to 99.999995% efficiency, and the difference between them can determine whether your cleanroom passes an EU GMP audit or fails.

HEPA filter classification is not a marketing designation — it is a precisely defined engineering specification governed by international standards. Choosing the wrong grade can mean either paying 3–5 times more than necessary (overspecifying) or failing regulatory compliance (underspecifying). This article explains the complete HEPA and ULPA classification system, how each grade is tested, where each grade belongs, and how to make the right choice for your application.

EN 1822:2019 is the European standard that defines HEPA and ULPA filter classification, and it is the most widely adopted standard globally for high-efficiency Air Filtration. It replaced earlier national standards (such as DIN 24183 in Germany and BS 3928 in the UK) and provides a unified system for testing efficiency at the Most Penetrating Particle Size (MPPS).

The standard defines HEPA grades H13 and H14, and ULPA grades U15, U16, and U17. The letter 'H' stands for 'HEPA' (High Efficiency Particulate Air) and 'U' stands for 'ULPA' (Ultra Low Penetration Air). The numbers indicate the efficiency tier — higher numbers mean higher efficiency.

Under EN 1822:2019, the key performance parameters are:

• MPPS Efficiency: The minimum efficiency of the filter at its Most Penetrating Particle Size. This is the 'worst case' particle size for the filter media — the size at which the filter is least efficient.
• Overall Efficiency: The integrated efficiency across all particle sizes. This is always higher than the MPPS efficiency because particles above and below MPPS are captured more effectively.
• Local Efficiency (Scan Test): The minimum efficiency measured at any point during a full-surface scan of the filter. This catches pinhole leaks and media defects.

Each grade is defined by three numbers: overall efficiency at MPPS, local efficiency (scan test minimum), and maximum allowable local penetration.

The Most Penetrating Particle Size (MPPS) is the particle diameter at which a filter is least efficient, and it is the basis for all EN 1822 classification. For HEPA and ULPA filters made from borosilicate glass microfiber media, MPPS is typically in the range of 0.15–0.3 μm.

I once had a customer ask why their H13 filter could capture 99.999% of 0.1 μm particles but only 99.95% of 0.3 μm particles. It is counterintuitive until you understand MPPS — the 0.3 μm particles are actually more difficult to capture because they are too large for effective diffusion and too small for effective impaction.

Not every filter labelled 'HEPA' has been individually tested and certified. A filter can be designed to meet H13 efficiency without every individual unit being scan-tested. EN 1822 requires two levels of testing: overall efficiency testing (batch/sample basis) and scan testing (every individual unit for H13 and above).

Scan testing is the physical procedure where a probe traverses the entire face of the filter at a controlled speed (≤5 cm/s for H14 certifiable results), measuring local penetration at every point. The purpose is to detect pinhole leaks, media defects, gasket bypass, or frame seal failures that would not show up in an overall efficiency test.

At KWS, every H13 and H14 filter we manufacture undergoes 100% scan testing in our ISO Class 7 cleanroom. Our KWS Plastic Frame High Efficiency Filters with H13–H14 grade media are individually scanned, and each unit ships with a certificate showing the overall efficiency and maximum local penetration measured.

Choosing between HEPA and ULPA (and between H13 and H14 within HEPA) is a decision with significant cost implications. ULPA filters cost 3–8 times more than HEPA filters of equivalent size, and they also create higher ΔP, requiring more fan power.

Here is the rule of thumb I use after 11 years: if your standard requires ISO Class 7 or 8 air cleanliness, H13 is adequate. If you need ISO Class 5 or 6, you need H14. If you need ISO Class 3 or 4, you are in ULPA territory. There is no shortcut — ULPA is required in semiconductor EUV lithography areas because a single 0.1 μm particle landing on a photomask can ruin an entire wafer batch worth $50,000–$200,000.

HEPA classification varies by region, and understanding the equivalences is critical for international procurement. A filter specified as "H13 per EN 1822" may be called "MERV 16–17" in North America, "Class 100" or "Type C" under older US standards, or "JIS Z 8122 Class 2" in Japan.

ISO 29463 is the international standard that attempts to harmonize HEPA and ULPA classification globally. It uses a different naming convention (ISO 45 H, ISO 35 H, ISO 25 U, etc.) where the number indicates the maximum allowable penetration in parts per 10,000. ISO 45 H allows 45 particles per 10,000 to penetrate (equivalent to 99.55% efficiency at MPPS), though this is considered a transition standard and EN 1822 remains the most referenced in industry practice.

Every individually scan-tested HEPA filter should come with a test certificate. Here is what to look for:

1. Filter identification: Serial number, model, dimensions, rated airflow. Confirm these match the filter you received.
2. Test standard: Should state EN 1822:2019 or the applicable version. If it only says "HEPA" without a standard reference, request more documentation.
3. Test aerosol: Should specify the test particles used (typically DEHS or PAO) and the particle size distribution (usually near the MPPS of the media).
4. Upstream concentration: Should be stated and should meet the minimum required by the standard (≥10^7 particles/cm³ for H13–H14).
5. Overall efficiency at MPPS: The single number that tells you whether the filter meets its grade. For H13, this must be ≥99.95%.
6. Maximum local penetration: The worst point found during the scan test. For H13, this must be ≤0.25%.
7. Initial ΔP: The pressure drop at rated airflow. This should match the datasheet range.
8. Test date and technician: Traceability matters for audits. The certificate should be signed or stamped.

Browse our full range of certified HEPA and high-efficiency filters to find the correct grade, size, and frame type for your application. Every KWS HEPA filter includes a complete EN 1822 scan test certificate.

At our Xiamen factory, we produce H13 and H14 HEPA filters in a dedicated ISO Class 7 cleanroom, with media handled under controlled conditions to prevent pre-contamination. Our production process includes:

• Media inspection: Every roll of borosilicate glass microfiber media is inspected for pinholes, thickness uniformity, and tensile strength before production begins.
• Mini-pleat forming: Media is pleated into a V-bank or mini-pleat configuration with aluminum separators or hot-melt glue bead spacers. Pleat height is controlled to ±1 mm.
• Frame assembly: ABS plastic frames (for our plastic frame line) or galvanised/stainless steel frames (for industrial applications) are assembled with the media pack. All frames receive a continuous urethane or silicone gasket.
• 100% scan testing: Every finished filter is tested on our automated scan test bench per EN 1822:2019. The test bench uses DEHS aerosol with an upstream concentration of ≥10^7 particles/cm³. Scan speed is set at 5 cm/s for H13 and 3 cm/s for H14.
• Pinhole leak marking: If a local penetration exceeds the grade limit, the leak location is marked on the filter frame, and the filter is either repaired (with approved sealant, followed by re-testing) or rejected.
• Packaging: Each filter is sealed in a polyethylene bag and packed in a corrugated carton with foam end caps. The test certificate is enclosed with the filter.

For ULPA-grade filters (U15 and above), we manufacture them on the same line but with additional quality controls: slower scan speed (≤2 cm/s), higher upstream concentration (≥10^8 particles/cm³), and additional edge seal inspection. Our KWS V-Shaped Plastic Frame HEPA/ULPA series covers H13 through U15 in standard modular sizes (610×610 mm, 610×305 mm, custom).

What is the difference between H13 and H14 HEPA filters?

H14 offers one order of magnitude higher efficiency than H13: 99.995% vs 99.95% at MPPS. This means an H14 filter allows 5 particles per 100,000 to penetrate, while H13 allows 50 particles per 100,000. H14 also requires a stricter scan test and typically has a higher initial ΔP (150–220 Pa vs 120–180 Pa). H14 is required for EU GMP Grade A aseptic processing areas; H13 is sufficient for Grade B backgrounds.

Is ULPA always better than HEPA?

Not for most applications. ULPA offers higher efficiency but at a cost: 2–8 times higher purchase price, 30–80% higher ΔP (increasing fan energy), faster loading in high-particulate environments, and a limited number of manufacturers who can certify them. Unless your application requires ISO Class 3 or cleaner air (semiconductor EUV lithography, nanotech research, biosafety Level 4), HEPA H13–H14 is almost certainly the better choice.

How is MPPS determined for a given filter media?

MPPS is determined empirically by testing filter media samples at multiple particle sizes (typically 0.03–0.5 μm) and identifying the size at which penetration is highest. For borosilicate glass microfiber media, MPPS is typically 0.15–0.3 μm. For e-PTFE membrane media, MPPS may shift to 0.05–0.15 μm. The filter manufacturer must determine and declare the MPPS for each media type used.

Can a HEPA filter lose efficiency over time?

Yes, but the pattern is not what most people expect. As a filter loads with particles, efficiency initially increases (captured particles add collection sites). However, if the filter becomes overloaded past its structural limit, several failure modes can reduce efficiency: media can tear or separate from the frame, gaskets can compress and allow bypass, and moisture damage can weaken the media structure. This is why ΔP monitoring and timely replacement are critical — an overloaded HEPA filter becomes the weakest link in the contamination control chain.

What does "99.97% at 0.3 μm" mean and how does it relate to EN 1822?

The 99.97% at 0.3 μm figure comes from the original US military standard (Mil-Std-282) and its commercial derivatives (IEST-RP-CC001). It was established in the 1950s when 0.3 μm was believed to be the MPPS of available filter media. EN 1822 modernised this by requiring testing at the actual MPPS of the specific media, which is typically 0.15–0.3 μm. H13 (99.95% at MPPS) is broadly equivalent to 99.97% at 0.3 μm, though the test methods differ.

Why do ULPA filters cost so much more?

ULPA filters require finer fiber media (submicron glass fibers vs 0.5–2 μm for HEPA), tighter manufacturing tolerances, slower scan testing (1–2 cm/s vs 5 cm/s), higher upstream aerosol concentrations (≥10^8 particles/cm³), and additional quality controls. The yield rate is also lower — a U16 production run may have 15–30% rejection rate versus less than 5% for H13. All of these factors contribute to the 3–8x price premium.

Can I replace an H14 filter with an H13 filter in the same housing?

Physically, if the dimensions match, yes. But the change may have regulatory consequences. If the application was designed for H14 (e.g., a pharmaceutical Grade A cleanroom), downgrading to H13 would violate the regulatory standard and could result in an audit finding. Always verify the regulatory requirements for your specific application before changing HEPA grade.

HEPA filter classification is not a marketing label — it is a precisely defined engineering specification that directly impacts regulatory compliance, product quality, and operating cost. The progression from H13 to U17 represents a 10,000x reduction in allowable penetration, but each step carries a cost penalty of 1.3–8x.

My advice after 11 years of designing and testing HEPA filters:

• For hospital operating theatres and food RTE rooms: H13 is adequate. Do not pay for H14 unless your regulatory standard requires it.
• For pharmaceutical Grade A aseptic processing: H14 is required by EU GMP Annex 1. Do not compromise — installing H13 will fail an audit.
• For semiconductor fabs requiring ISO Class 3–4: U15–U16 ULPA is necessary. The cost is justified by the value of the product being protected.
• For general cleanrooms (ISO Class 7–8): H13 is the standard. No need for higher grades.
• Always demand individual scan test certificates. A HEPA filter without a certificate is just a dense piece of media. The certificate is your proof that it meets the grade.