What is a MERV rating?
In one line: MERV (Minimum Efficiency Reporting Value) rates how well a filter captures particles, on a scale of 1 to 16 — higher means it traps smaller particles. MERV-13 is the practical sweet spot for indoor air quality: it catches fine particles well without choking airflow.
How the scale works
| MERV | Captures | Typical use |
|---|---|---|
| 1–4 | Large dust, lint | Basic furnace/AC protection |
| 5–8 | Mould spores, dust mite debris | Better home HVAC |
| 9–12 | Fine dust, some PM2.5 | Higher-grade HVAC |
| 13–16 | Most PM2.5, bacteria, smoke | Clean-air / hospital-grade HVAC |
The higher the number, the smaller the particles caught — but also the more resistance to airflow, which is why very high MERV filters need a system (or fan) strong enough to push air through them.
Why MERV-13 is the benchmark
MERV-13 captures a large share of fine particles — including much of the PM2.5 that matters most for health, plus smoke and many airborne microbes — while still allowing enough airflow to be practical. It's the grade widely recommended for improving indoor air, and it's what many DIY clean-air builds like the Corsi-Rosenthal box use.
MERV vs HEPA
They're two different scales. HEPA is a single high bar (99.97% at 0.3 microns); MERV is a graded 1–16 scale, where MERV-13 is high but below HEPA. What matters in practice is airflow × efficiency — a MERV-13 with strong airflow can clean a room faster than a HEPA with weak airflow. Full comparison in HEPA vs MERV-13.
Next step
Want the clean-air grade sorted for you? Browse HEPA and MERV-13 units in the CleanAirKits store.
FAQ
What MERV rating is best for home air quality? MERV-13 — it captures most fine particles while keeping airflow practical.
Is a higher MERV always better? Not necessarily — very high MERV restricts airflow, so it needs a system strong enough to handle it. Match the filter to the fan.