Air purifier listings throw around terms such as H13, true HEPA, activated carbon and 'medical grade'. They are not interchangeable, and some are just marketing. This guide explains what each filter layer does so you can read a listing with confidence.
The short version: HEPA handles particles, carbon handles some odours and gases, and neither is a miracle.
HEPA: the particle filter
A HEPA filter is a dense mat of glass fibres that traps particles as air passes through. It captures dust, pollen, mould spores and the fine particles known as PM2.5. It does not remove gases or smells.
HEPA grades come from standards. Under the European EN 1822 standard, H13 is rated to capture at least 99.95% of particles at the most penetrating size. H12 is rated at 99.5%. 'True HEPA' is a US term, usually meaning 99.97% at 0.3 micrometres.
H13 vs H12: does it matter?
H13 is rated to catch more fine particles than H12, but the difference is small for everyday use. A well-sealed H12 unit with a good CADR can outperform a leaky H13 unit.
If the price difference is small, choose H13. If not, put the money into a bigger CADR and a sealed housing.
Beware 'HEPA type' and 'medical grade'
'HEPA type', 'HEPA style' and 'medical grade' are not defined grades. They may be a good filter or a plain one, and the listing does not tell you which. Prefer listings that name H13, H12 or a stated test standard.
Also check that the unit is sealed. Air takes the easiest path, and a filter with gaps around its edges lets particles bypass it.
Activated carbon: smells and some gases
Activated carbon is porous and adsorbs odour molecules and some gases. It helps with cooking smells, smoke and pet odours. How well it works depends on how much carbon is in the filter. A thin, black-coated sheet holds very little and fills up quickly. A thick bed of granules holds much more.
Carbon does not remove particles. It also wears out, so replace it on schedule.
Pre-filters
A pre-filter is a coarse mesh that catches hair, fibres and large dust. It protects the main filters and is usually washable. Rinse it only if the maker says so, and dry it fully before you put it back.
Other layers: UV, ionizers and plasma
UV lamps, ionizers and 'plasma' modules are extras. They are not substitutes for a HEPA filter, and some produce ozone. Treat them as optional, and look for an ozone-free statement if you want one in a bedroom.
Frequently asked questions
Is H13 HEPA better than true HEPA?
They are rated under different standards. H13 under EN 1822 is rated for at least 99.95% capture, and true HEPA under the US standard is 99.97% at 0.3 micrometres. For home use, both are very good if the unit is sealed.
Does a HEPA filter remove smells?
No. HEPA captures particles. Activated carbon is the layer that helps with smells.
Can I wash a HEPA filter?
Generally no. Washing damages the fibre layer. Only wash parts that the maker says are washable, such as the pre-filter.
