MERV Ratings

Selecting the proper MERV for your air filters to protect people and processes. The American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) provides guidance as to what filter efficiency should be applied to protect building occupants or processes and considers HVAC equipment limitations, the airborne contaminants of concern and the economies of air filter expenditures. Air filters are manufactured in various forms and efficiencies. The efficiency is normally provided in the form of a minimum efficiency reporting value (MERV). To ensure a filters performance over time the air filters MERV-A value should also be provided. Common recommendations are based upon environment research that spans back to ASHRAE’s inception in 1959 and other authorities like the Centers for Disease Control (CDC), National Institutes for Health (NIH) and even the Nuclear Regulator Committee (NRC). The minimum efficiency reporting value, is a number from 1 to 16 that is relative to an air filter’s efficiency based upon particle size. The higher the MERV, the more efficient the air filter is at removing particles. At the lower end of the efficiency spectrum a fiberglass or polyester panel filter may have a MERV of 4 or 5. At the higher end, a MERV 14 filter is typically the filter of choice for critical areas of a hospital (to prevent transfer of bacteria and infectious diseases). Higher MERV filters are also capable of removing higher quantities of extremely small contaminant (particles as small as 1/300 the diameter of a human hair). A higher MERV creates more resistance to airflow because the filter media becomes denser as efficiency increases. For the cleanest air, a user should select the highest MERV filter that their unit is capable of forcing air through based on the limit of the unit’s fan power. Additional considerations include the likely size of the offending airborne contaminant, whether the human lung is susceptible to the malady, the likely volume of contaminant and mortality base upon offering no protection at all. Some common recommendations include MERV 13 for office buildings, MERV 14 for medical facilities and MERV 8 for outside air intakes in urban areas. Camfil recommends the following based upon literature evaluation and best case scenario for protection based upon cognizant authorities.  

Warehouse, storage, shop and process areas, mechanical equipment rooms, electrical control rooms, protection for heating and cooling coils	MERV 8
Special process areas, electrical shops, paint shops, average general offices and laboratories	MERV 11
Analytical laboratories, electronics shops, drafting areas, conference rooms, above-average general offices	MERV 13
Hospitals, pharmaceutical R&D and manufacturing (non-aseptic areas only), some clean (“gray”) rooms	MERV 14
Aseptic areas in hospital and pharmaceutical R&D and manufacturing. Cleanrooms in film and electronics manufacturing, radioactive areas, etc.	Pre-filtration of MERV 8 and MERV 15 plus HEPA*
* HEPA filters are high efficiency particulate air (HEPA) filters. They are manufactured using recommended practices has published by the Institute of Environmental Technologies, not ASHRAE.