What is a MERV Rating?

Updated September 15, 2015
HVAC air filter being removed
Do you know the MERV rating of your air filter? They can improve air quality but only if they are approved for your system. Check with your HVAC manufacturer for MERV limits. (Photo by Summer Galyan)

Minimum Efficiency Reporting Value (MERV) rates the efficiency of air filters at removing airborne particles from buildings. What is the MERV rating for your air filter?

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What is a MERV rating?

Minimum Efficiency Reporting Value (MERV) rates the efficiency of air filters based on a 20 point scale. The lower the rating, the less effective that filter is at removing airborne particles from buildings, such as pollen, carpet fibers, bacteria and viruses. For example, a MERV 4 air filter can remove larger particulates from the air, such as dust mites and cockroach debris, but cannot filter viruses or smoke, which can be filtered by an MERV 17 air filter.

The MERV scale was created in 1987 by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) to not only improve indoor air quality, but to address energy efficiency. Since its inception, this scale has helped improve the air quality of residential, commercial and medical facilities across America.

What does MERV Mean on Air Filters?

MERV ratings help simplify the complicated world of indoor air quality - sometimes several filters with different MERV ratings are used in one building. For example, some medical facilities require two filter banks, one filter bank with a MERV 7 air filter and the second with a MERV 14 air filter.

While commercial and medical facilities can be complicated, understanding MERV ratings for homes is relatively simple, with only one filter needed to ensure superior air quality.

Most home HVAC systems are delivered with air filters in the 1-4 MERV rating group. ASHRAE indicates this lower rating is simply to protect internal components of the system and higher MERV rated air filters can be used for homes, typically in the 5-8 range.

But don't go out and buy an air filter with the highest MERV rating possible! If you are curious about improving the MERV rating of the air filters in your home be sure to check with the HVAC manufacturer. The higher the MERV rating, the higher the air resistance, so manufacturers typically have a MERV rating limit for their system.

MERV Filters

MERV ratings run on a scale of 1 to 20. Here's a quick rundown of each, what they filter and where they are typically used:

  • MERV 1-4 Air FiltersWhat they filter: Dust mites, cockroach debris, pollen, certain types of dust and fibers from carpet and textiles.    Where are they used: In residential AC units.

  • MERV 5-8 Air FiltersWhat they filter: Dust mite debris, animal dander, mold, spores and certain sprays (fabric protectors, cleaning aids, etc.)Where they are used: In residences, commercial spaces and industrial settings.

  • MERV 9-12 Air FiltersWhat they filter: Some bacteria, milled flour, certain types of dust (humidifiers, lead, etc.), automobile emissions and mist droplets.    Where they are used: Also used in residential, commercial and industrial HVAC units, as well as in some hospital labs.

  • MERV 13-16 Air FiltersWhat they filter: Bacteria, droplets from sneezes, most oils, some smoke and paint pigments.    Where they are used: In hospitals and operating rooms.

  • MERV 17-20 Air FiltersWhat they filter: Carbon dust, viruses, all smoke and sea salt.    Where they are used: Manufacturing facilities that produce sensitive electronic components and pharmaceutical products.

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