MERV stands for "Minimum Efficiency Reporting Value". It is a measurement scale designed by the ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers. The independent scale allows for accuracy in measuring a filters ability to capture contaminates. This can help gauge needs for health and costs.
For example, according to "Residential Air Cleaners (2nd Edition): A Summary of Available Information", 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 table below shows various MERV ratings and their typical applications.
|MERV||Min. particle size||Typical controlled contaminant||Typical Application|
|1–4||> 10.0 μm||Pollen, dust mites, cockroach debris, sanding dust, spray paint dust, textile fibers, carpet fibers||Residential window AC units|
|5–8||10.0–3.0 μm||Mold, spores, dust mite debris, cat and dog dander, hair spray, fabric protector, dusting aids, pudding mix||Better residential, general commercial, industrial workspaces|
|9–12||3.0–1.0 μm||Legionella, Humidifier dust, Lead dust, Milled flour, Auto emission particulates, Nebulizer droplets||Superior residential, better commercial, hospital laboratories|
|13–16||1.0–0.3 μm||Bacteria, droplet nuclei (sneeze), cooking oil, most smoke and insecticide dust, most face powder, most paint pigments||hospital & general surgery|