HEPA Filter Standards: True HEPA, HEPA-Type, and ULPA Classifications
Volume I · May 2026 · 882 words
The term "HEPA" appears on dozens of consumer air purifiers, but it conceals a hierarchy of filter grades with orders-of-magnitude differences in particle removal efficiency. A filter labeled "HEPA-type" or "HEPA-like" has no defined standard and may capture as little as 85% of 0.3 µm particles. A true H13 HEPA filter captures 99.95%. This article explains what each classification means, how it is tested, and why the distinction matters for respiratory health.
The EN 1822 Standard
HEPA filter performance is defined by the European standard EN 1822 (also adopted as ISO 29463), which classifies filters by their efficiency at the Most Penetrating Particle Size (MPPS). The MPPS is the particle diameter at which the filter is least efficient — typically 0.1–0.3 µm for HEPA media. Particles smaller than the MPPS are captured more effectively by diffusion (Brownian motion drives them into filter fibers); particles larger than the MPPS are captured by interception and impaction. The MPPS is the valley between these two capture mechanisms.
| Class | Efficiency at MPPS | Penetration | Typical application |
| E10 (EPA) | ≥ 85% | ≤ 15% | Pre-filtration, HVAC |
| E11 (EPA) | ≥ 95% | ≤ 5% | Residential HVAC, some purifiers |
| E12 (EPA) | ≥ 99.5% | ≤ 0.5% | Budget "HEPA" purifiers |
| H13 (HEPA) | ≥ 99.95% | ≤ 0.05% | Medical-grade purifiers, cleanrooms |
| H14 (HEPA) | ≥ 99.995% | ≤ 0.005% | Pharmaceutical, semiconductor |
| U15 (ULPA) | ≥ 99.9995% | ≤ 0.0005% | Semiconductor fabrication |
| U16 (ULPA) | ≥ 99.99995% | ≤ 0.00005% | Advanced cleanrooms |
| U17 (ULPA) | ≥ 99.999995% | ≤ 0.000005% | Ultra-high purity environments |
The practical difference between H13 and H14 in a residential setting is small: both will reduce PM2.5 to near-zero steady-state levels. The difference between E11 and H13 is substantial: an E11 filter passes 100× more particles through the media. For a person with asthma or COPD, that difference translates to a measurably higher particle burden in the breathing zone.
"True HEPA" vs "HEPA-Type"
"True HEPA" is not a technical term, but in consumer marketing it generally indicates H13-class filtration (≥ 99.95% at MPPS). The Coway Airmega AP-1512HH and Levoit Core 300 both use True HEPA H13 filters. The term is a response to "HEPA-type," "HEPA-like," and "HEPA-style" — marketing phrases with no standardized definition. A "HEPA-type" filter may use a lower-efficiency media (E10–E12) or may meet the efficiency specification only for a subset of particle sizes, failing at the MPPS.
How to verify: look for the EN 1822 class (H13 or H14) in the product specifications. If the manufacturer does not publish the filter class, assume it is not H13. A claim of "99.97% at 0.3 µm" without specifying the test standard (EN 1822, IEST-RP-CC001, or MIL-STD-282) is ambiguous — efficiency varies with test conditions, and a filter tested at low face velocity will show higher efficiency than the same filter at its rated airflow.
ULPA: When HEPA Is Not Enough
ULPA (Ultra-Low Penetration Air) filters, classified U15 through U17, remove ≥ 99.9995% of particles at MPPS. The filter media is denser, the pressure drop is higher, and the airflow per unit area is lower. ULPA filters are used in semiconductor fabrication where a single sub-micron particle can ruin a wafer. In residential air purification, ULPA provides no measurable health benefit over H13: the additional 0.045% efficiency improvement captures particles that would have been captured by the next pass anyway, given that residential purifiers recirculate room air multiple times per hour.
Purifiers marketed with ULPA filters, such as the Medify MA-40, achieve higher single-pass efficiency but often at a higher pressure drop that reduces CADR for a given fan speed. The net effect on room-cleaning rate can be worse than an H13 purifier with higher airflow. Single-pass efficiency matters less than clean air delivery rate for recirculating room air.
Filter Construction and Seal Integrity
A HEPA filter's rated efficiency assumes no bypass — all air passing through the purifier must pass through the filter media. Gaps between the filter frame and the purifier housing allow unfiltered air to bypass the media entirely. A purifier with an H13 filter but a poor frame seal may deliver E10-class performance in practice. Quality purifiers use compression gaskets or foam seals around the filter perimeter; budget units rely on a simple friction fit that degrades as filters are repeatedly replaced.
The filter media itself is typically borosilicate glass fibers (in industrial HEPA) or melt-blown polypropylene (in consumer purifiers). Glass fiber media maintains efficiency over time because it does not rely on electrostatic charge. Some polypropylene media is electret-treated — an electrostatic charge applied during manufacturing that enhances initial efficiency. As the charge dissipates over months of use, efficiency can decline by several percentage points. This is not a filter failure, but it means a filter that tested at 99.97% efficiency when new may drop to 99.5% as the charge decays — still within H13 specification but representing a measurable decline.