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 micrometers. 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 grouping MERV ratings by particle size:
While the smallest MERV value in each row has no minimum requirement for filtering that row's particle size, it does have stricter requirements for all larger particle sizes than any smaller MERV value. For example, MERV 13 has no minimum requirement for removing 0.3–1.0 μm particles (the standard specifies <75%) but has higher minimum requirements for removing 1.0–3.0 μm, 3.0–10.0 μm, and > 10 μm particles than MERV 12 and all smaller MERV values. All other MERV values on each row do have minimum removal percentages for that row's particle size.
- Wilkinson, Ron. "Air Filters: New Facilities, New Standard" (PDF). Retrieved 2007-03-29.
- "Residential Air Cleaners (2nd Edition): A Summary of Available Information" (PDF). EPA. Archived from the original on February 1, 2013. Retrieved 2012-08-20.CS1 maint: unfit url (link)
- ANSI/ASHRAE Standard 62.1-2007 requires a filter of at least MERV 6 efficiency for residential applications in the US.
- MERV values of 17–20 are not part of the official standard specification. These may be roughly equivalent to HEPA or ULPA filters (http://www.epa.gov/iaq/pubs/residair.html#Defining_Efficiency_and_Effectiveness) but the specifications are fundamentally different.
- M.N.Rama Rao & Company. "Industrial Filters (Eurovent and ASHRAE Classifications)". Retrieved 2007-09-19.
- Newell, Donald (February 2006). "Interpreting Filter Performance: The meaning behind the terminology of ASHRAE standards 52.1 and 52.2" (PDF). HPAC Engineering. Archived from the original (PDF) on 2009-01-07. Retrieved 2009-05-11.