What is MERV?
- pourlabs
- Feb 1, 2017
- 2 min read
Before we get into removing molecular contaminants we need to first establish a baseline understanding of particulate filtration. This starts with the Minimum Efficiency Reporting Value (MERV).
I should also preface that I typically will reference to Camfil for education as they seem to be the least commercial of all the global filter manufacturers and publish data that is backed in facts and R&D.
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. (https://catalog.camfil.us/air-filtration-faqs/merv-ratings.html)
This is the most helpful chart to understand the MERV ratings. Anything above MERV 16 would qualify as High Efficiency Particulate Arrestance (HEPA).
As with any standard, manufacturers found a way to cheat the system and began to electrostatically charge their synthetic media filters to qualify for a higher MERV rating. This would allow a filter to pass ass a MERV 14 filter initially to meet healthcare requirements, but would quickly lose that charge and drop to a MERV 11 or worse in a matter of weeks or less if exposed to diesel fumes. This is why the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE), created appendix J in their 52.2 code which requires manufacturers to remove the charge from their filters. Always look for a MERV-A rating. If there is not one, then the manufacturer is hiding something and will most certainly then shift your attention to the pressure drop argument.
However, this is a website and blog dedicated to molecular filtration, so this will be all the data provided on particle filters. Do your research and don't just assume a filter is just a filter.
Comentarios