When you hear about MERV, do your thoughts turn to day-time talk shows or night-time air quality? MERV (minimum efficiency reporting value) is actually an acronym for numeric values applied to air filters, based on their ability to remove particles from the atmosphere. Using this rating system, consumers can select a particle-removal air filter by viewing the efficiency with which it removes airborne particles from the air stream. This scale was developed by the American Society of Heating, Refrigeration and Air-Conditioning Engineers, and rates filters ona a scale of one to twenty.
One of the best ways to address residential indoor air pollution is to control or eliminate the source of the pollutants and to ventilate the home with clean outdoor air. But ventilation can be limited by weather conditions or the levels of filtration devices. Additional air filtration can be achieved with filters installed in the HVAC ductwork that can clean the air in the entire house.
Flat or panel air filters with a MERV score of one to four are most commonly used in residential furnaces and air conditioners. These filters are designed to protect HVAC equipment from the build-up of unwanted materials on surfaces including fan motors and heating or cooling coils, not for direct indoor air quality reasons. They have low efficiency ratings on smaller airborne particles and medium efficiency on larger particles. (Smaller particles commonly found within a house that are not affected by these filters include viruses, bacteria, some mold spores, a significant fraction of cat and dog allergens, and a portion of dust mite allergens).
Medium efficiency filters with a MERV of five to thirteen are considered reasonably efficient at removing small to large airborne particles. Filters with a higher MERV score (between seven and thirteen) are considered almost as effective as true HEPA (high efficiency particulate air) filters at controlling most airborne indoor particles and are generally quieter and less expensive than a HEPA filter. (HEPA filters are composed of a mat of randomly arranged fibers. The fibers are typically composed of fiberglass, with diameters between 0.5 and 2.0 micrometers.)
Most MERV air filters are good at capturing larger airborne particles, such as dust, pollen, dust mite allergens, some molds, and animal dander. However, because these particles settle quickly, air filters are not completely effective at removing them from indoor areas. (Although activities such as walking and vacuuming can stir up particles, most of the larger particles will resettle before an air filter can remove them).
In addition, some residential HVAC systems may not have enough fan or motor capacity to accommodate higher efficiency MERV filters. Therefore, the HVAC manufacturer’s information should be checked prior to upgrading filters to determine whether it is feasible to use more efficient filters.
Source: Huffman Inspections http://www.huffmaninspections.com