The two ratings, in plain English
HEPA (H11–H13) is a lab standard for a single filter's capture at its most-penetrating particle size — H13 traps ≥99.95%. MERV-13 is the top of the everyday HVAC scale, capturing roughly 93% of particles across the range that matters indoors (PM2.5, pollen, smoke).
The catch people miss: a filter's rating is not the same as a machine's clean-air delivery. Dense HEPA media has high airflow resistance, so small sealed units push relatively little air through it — and get loud doing so.
| Sealed HEPA unit | High-airflow MERV-13 box | |
|---|---|---|
| Single-pass capture | 99.95%+ (H13) | ~93% |
| Airflow resistance | High | Low |
| Air moved (CADR) | Limited by the fan | Very high — clears rooms fast |
| Noise at full clean | 55–65 dB | <35 dB |
| Filter cost | £40–£80 proprietary | £58–£75 standard pair |
Why capture rate isn't the whole story
Cleaning a room is capture rate × air moved, repeated over time. A 99.95% filter that only processes a trickle of air loses to a 93% filter that cycles the whole room's air several times an hour. Over a night, the high-airflow MERV-13 box typically wins on particles actually removed — which is what you breathe.
When HEPA genuinely makes sense
- Tiny sealed spaces (a car cabin, a single desk zone).
- Clinical settings needing certified single-pass performance.
- Specific ultrafine-particle concerns where certified H13 is specified.
For a bedroom, living room, classroom or office, high-airflow MERV-13 is the pragmatic winner on clean air per pound and per decibel.