Definition
Minimum Efficiency Reporting Value — a 1–16 scale from the ASHRAE 52.2 test reporting how reliably a filter captures particles by size. MERV 8 is the residential baseline, 11 the allergy upgrade, 13 the health tier.
What does a MERV number actually promise?
It's the filter's minimum capture efficiency across three particle-size bands in the ASHRAE 52.2 lab test — smoke-sized (0.3–1 µm), fine dust (1–3 µm), and pollen/mite-sized (3–10 µm). It is a capture report card by particle size, not a quality badge: a filter can catch 99% of enormous pollen while doing nearly nothing about tiny wildfire smoke.
Is a higher MERV always better?
No — capture and airflow resistance rise together, and your blower has a fixed pressure budget (typically about 0.5 inches of water column for the whole air path). Past what the system can afford, a denser filter starves airflow and ages equipment early. The engineering answer is surface area: a 4–5 inch media cabinet captures at MERV 11–13 while resisting less than a cheap 1-inch pleat.
In the Puget Sound
Wildfire smoke particles run 0.4–0.7 µm — the band that only MERV 13+ meaningfully captures. For Puget Sound smoke season: MERV 13 in a media cabinet, plus a portable HEPA in occupied rooms.
Related terms
Go deeper on MERV
Not sure what MERV means for your home?
Ask the licensed team that works with it every day — clear answers and an upfront price before any work begins.
Trade: Heating & Air