Minimum efficiency reporting value, commonly known as MERV rating is a measurement scale designed in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to rate the effectiveness of air filters. The scale "represents a quantum leap in the precision and accuracy of air-cleaner ratings"[1] and allows for improved health, reduced cost and energy efficiency in heating, ventilation and air conditioning (HVAC) design. For example, a HEPA filter is often impractical in central HVAC systems due to the large pressure drop the dense filter material causes. Experiments indicate that less obstructive, medium-efficiency filters of MERV 7 to 13 are almost as effective as true HEPA filters at removing allergens, with much lower associated system and operating costs.[2]
The scale is designed to represent the worst case performance of a filter when dealing with particles in the range of 0.3 to 10 micrometres. The MERV rating is from 1 to 16. Higher MERV ratings correspond to a greater percentage of particles captured on each pass, with a MERV 16 filter capturing more than 95% of particles over the full range.
Below is a table of example MERV ratings:
| MERV | Min. particle size | Typical controlled contaminant [2] | Typical Application [2] |
|---|---|---|---|
| 17–20[3] | < 0.3 μm | Virus, carbon dust, sea salt, smoke | Electronics & pharmaceutical manufacturing cleanroom |
| 13–16 | 0.3–1.0 μm | Bacteria, droplet nuclei (sneeze), cooking oil, most smoke and insecticide dust, most face powder, most paint pigments | hospital & general surgery |
| 9–12 | 1.0–3.0 μm | Legionella, Humidifier dust, Lead dust, Milled flour, Auto emission particulates, Nebulizer droplets | Superior residential, better commercial, hospital laboratories |
| 5–8[4] | 3.0–10.0 μm | Mold, spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix | Better residential, general commercial, industrial workspaces |
| 1–4 | > 10.0 μm | Pollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, carpet fibers | Residential window AC units |