HEPA vs MERV-13: what's the difference?
In one line: both capture the fine PM2.5 particles that matter for health. True HEPA grabs a little more of the very smallest particles, but restricts airflow; MERV-13 lets a fan move much more air for the same noise — so in a real room a high-airflow MERV-13 unit often delivers cleaner air per pound.
What the two ratings mean
HEPA (High-Efficiency Particulate Air) is a standard: a true HEPA filter captures at least 99.95% of particles at the hardest-to-catch size (around 0.3 microns). It's a dense, sealed filter, which is why it's very effective — and why it resists airflow.
MERV-13 comes from the MERV scale (Minimum Efficiency Reporting Value, 1–16) used for HVAC filters. MERV-13 captures roughly 90%+ of particles in the 1–3 micron range and a high share of PM2.5. It's less dense than HEPA, so a fan pushes far more air through it.
Where they differ in practice
| True HEPA | MERV-13 | |
|---|---|---|
| Captures PM2.5? | Yes (99.95% @ 0.3µm) | Yes (high share; ~90%+) |
| Airflow resistance | High (chokes the fan) | Low (fan moves more air) |
| Clean-air delivery | Lower per watt of fan | Higher per watt of fan |
| Noise for same clean air | Higher | Lower |
| Filter cost | Often proprietary, £50–80/yr | Standard media, cheaper |
So which should you choose?
For a hospital operating theatre or a cleanroom, HEPA's extra capture at the finest sizes matters. For a home dealing with dust, pollen, pet dander, smoke and everyday PM2.5, what matters most is moving a lot of clean air quietly and cheaply — which is where high-airflow MERV-13 shines. This is the principle behind the Corsi-Rosenthal box: surround a fan with several MERV-13 filters so it delivers a very high CADR at low noise and low cost. The practical test isn't "which filter grade is highest" but "which unit delivers the most clean air, quietly, at a price you'll leave switched on."
Next step
Compare units on measured clean-air delivery, noise and running cost at Best Air Purifier UK, or read the Corsi-Rosenthal explainer.
FAQ
Is MERV-13 as good as HEPA for viruses and smoke? Both capture the fine aerosol and smoke particles that matter; HEPA edges it at the very smallest sizes, but MERV-13's higher airflow means more total clean air per hour, which often wins in a real room.
What about "HEPA-type" filters? "HEPA-type" or "HEPA-like" is not the certified HEPA standard and can capture far less. Look for "true HEPA" (H13/H14) or a genuine MERV-13 rating.