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"^[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

References

1. ^ Wilkinson, Ron. "Air Filters: New Facilities, New Standard". http://www.foustco.com/_fileCabinet/ProductInstructions/HVACFilters/merv_explanation.pdf. Retrieved 2007-03-29. 
2. ^ ^{a b c} "Residential Air Cleaners (2nd Edition): A Summary of Available Information". EPA. http://www.epa.gov/iaq/pubs/residair.html. Retrieved 2011-05-24. 
3. ^ MERV values of 17–20 are not part of the official standard test. These are sometimes compared to HEPA filters but the specifications are fundamentally different.
4. ^ ANSI/ASHRAE Standard 62.2-2007 requires a filter of at least MERV 6 efficiency for residential applications in the US.

• M.N.Rama Rao & Company. "Industrial Filters (Eurovent and ASHRAE Classifications)". http://www.mnrfilters.com/automotive.html. Retrieved 2007-09-19. 
• Newell, Donald (February 2006). "Interpreting Filter Performance: The meaning behind the terminology of ASHRAE standards 52.1 and 52.2". HPAC Engineering. http://www.emcorservicesnynj.com/news/FilterPerformanceByDN.pdf. Retrieved 2009-05-11. 

External links

http://www.epa.gov/iaq/pubs/residair.html