HEPA is a pass mark on a test, not a type of material
HEPA is not a material, a brand, or a patented technology.
It is a pass mark. A filter either meets the efficiency threshold or it does not.
Two filters can both carry the word and be built from entirely different media.
What the label promises is a number. Everything else is the manufacturer's choice.
H13 means 99.95% of the hardest particles to catch
Under the European standard EN 1822, an H13 filter removes 99.95% of particles at its worst-performing size.
H14 removes 99.995%.
The phrase "worst-performing size" is doing most of the work in that sentence.
Engineers call it the MPPS โ most penetrating particle size. It usually sits somewhere between 0.1 and 0.3 microns.
Below that band, particles stop behaving like tiny footballs and start drifting on the air molecules around them.
That drift makes them collide with the fibres rather than sail between them.
So a HEPA filter catches a 0.05 micron particle more reliably than a 0.2 micron one.
The rating describes the low point of the curve, not the ceiling.
The 0.3 micron figure is a worst case, not a cut-off
American packaging quotes 99.97% at 0.3 microns, which comes from the US Department of Energy definition.
British and European boxes quote EN 1822 grades instead.
A HEPA filter performs worst at around 0.3 microns, which is precisely why the standard insists on testing it there.
The two systems measure slightly different things, so the headline percentages are not directly comparable.
Neither of them means the filter stops working below 0.3 microns.
Combustion soot, cooking fumes and virus-carrying droplet nuclei are all smaller than that, and all get caught.
"True HEPA" is marketing; the grade underneath is the standard
"True HEPA" has no legal definition. No body issues it and no test defends it.
The phrase exists because "HEPA-type" and "HEPA-style" were being printed on filters that had failed the real thing.
Treat any hyphenated variant as a warning rather than a reassurance.
Look for an explicit EN 1822 grade instead.
| Grade | Class | Efficiency at MPPS |
|---|---|---|
| E10 | EPA | 85% |
| E11 | EPA | 95% |
| E12 | EPA | 99.5% |
| H13 | HEPA | 99.95% |
| H14 | HEPA | 99.995% |
E-grades are EPA โ efficient particulate air. A rung below HEPA, and not the same claim.
Most domestic purifiers sit at H13, which is the sensible place for them to sit.
H14 belongs in operating theatres and is largely wasted in a sitting room.
A filter grade says nothing about how quickly the room gets clean
Efficiency is measured on the air that passes through the filter.
It tells you nothing about how much air passes through per hour.
That figure is CADR, and it is what decides whether a purifier can keep up with the room you put it in.
An H13 cartridge behind a weak fan will clean a large room very slowly.
An H13 in a leaky housing may not manage even that, because air slipping round the edge of a filter is never tested by anyone.
So read the grade, then read the CADR, then check the room size the manufacturer quotes alongside it.
We take that combination apart in our Levoit Vital 200S-P review.
Outdoor air sets the floor that any indoor filter has to work up from.
DEFRA publishes measured pollutant levels by region, updated through the day.
