HEPA Filters Explained (for Cordless Hoovers)

By cordlesshoover.com · Updated 16 Oct 2026

A HEPA filter is a dense mat of fine fibres that traps at least 99.95% of the hardest-to-catch particles (for an H13 grade under the European standard). In a hoover it only helps if the whole machine is sealed, because dust that leaks around the filter, through the bin seal or between body joints never reaches it. For allergy sufferers, "sealed whole-machine filtration" is the phrase that matters most.

What HEPA actually means

HEPA stands for High Efficiency Particulate Air. In the UK and Europe, filters are graded under EN 1822 (and the related international standard ISO 29463). The grade is based on how efficiently the filter captures particles at its most penetrating particle size (MPPS), typically around 0.1–0.3 microns. That's the size that slips through most easily, so a filter rated at MPPS is even better at larger allergens such as pollen (roughly 10–100 microns) and dust mite droppings (around 10–40 microns).

How fibres catch particles

HEPA isn't a sieve. It traps particles three ways:

• Impaction: large particles can't follow the air as it bends round fibres and crash into them.
• Interception: mid-sized particles following the airflow brush against a fibre and stick.
• Diffusion: very small particles bounce randomly as they collide with air molecules (Brownian motion) and eventually hit a fibre.

Impaction and interception work best on larger particles and diffusion on the smallest, which is why there's a "worst" size in the middle, the MPPS.

Filter grades compared

The 2009 revision of EN 1822 renamed the old H10–H12 grades as "EPA" (E10–E12), though many brands still advertise "H11" or "H12". You'll also see the US definition of HEPA, which is 99.97% at 0.3 microns, roughly comparable to H13 in practice.

Why a sealed system matters more than the label

A filter only cleans the air that passes through it. In a hoover, air can escape before the filter at:

• The bin seal and lid flap
• Joints between the cyclone, motor housing and body
• Around the edges of the filter itself if the housing isn't gasketed

Even a small leak lets fine dust bypass an H13 filter completely. That's why emissions tests on the whole machine, rather than filter-only ratings, are the meaningful measure. Some manufacturers publish whole-machine filtration claims (for example, Dyson describes its higher-end models as capturing 99.99% of particles down to 0.3 microns with sealed filtration). Independent testers and allergy charities' approval schemes also assess the full machine.

Filter types in cordless hoovers

Bagged machines such as the Henry Quick and Gtech Pro 2 seal dust inside the bag, which makes emptying far less dusty; see bagged vs bagless cordless hoovers.

How to wash a cordless hoover filter

1. Check the manual: only wash filters marked washable.
2. Remove the filter and tap it over the bin outdoors to loosen dust.
3. Rinse under cold running water only. No soap, detergent or dishwasher; they damage the fibres and leave residue.
4. Squeeze or shake gently until the water runs clear. Don't scrub pleated HEPA media with a brush.
5. Dry for at least 24 hours at room temperature, away from radiators and tumble dryers.
6. Refit only when completely dry. A damp filter can grow mould, smell and damage the motor.

Most brands suggest washing monthly. More detail in how to clean a cordless hoover.

When to replace a filter

• It stays grey or clogged after washing.
• Pleats are torn, flattened or the rubber seal is cracked.
• Suction is weak after washing and a blockage has been ruled out; see cordless hoover losing suction.
• The hoover smells musty even when clean.

Replacement filters usually cost £10–£35 depending on brand. Genuine filters fit and seal properly; cheap copies sometimes don't, which defeats the point of HEPA.

Does HEPA reduce suction?

Denser media resists airflow more, so H13 filters need a well-designed air path and a stronger motor to maintain suction. A clean H13 filter on a good machine isn't a problem; a clogged one is. That's another reason to keep it clean. For how airflow relates to cleaning, see suction power explained.

Choosing a hoover for allergies

Look for H13 filtration, a sealed system with whole-machine emission claims, a bin that empties with a single push straight into a bag, and ideally a self-emptying dock or bagged design. Our best cordless hoover for allergies page applies these criteria to current models.