Minimum efficiency reporting value
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” 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.
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 ||Typical Application |
|17–20||< 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||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|