MERV Ratings

Minimum Efficiency Reporting Values (or MERV) ratings indicate a filter's efficiency in capturing airborne particles and contaminants, such as lint, carpet fibers, dust, allergens like pollen and mold, and even bacteria and viruses. Developed by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), MERV ratings provide a scale for ranking filters using this criterion.

• MERV rankings range from 1 to 16.
• The higher the MERV rating, the more effective the filter is at trapping small particles (between 0.3 and 10 microns (µm)).
• Any filter rated above MERV 6 must be tested to assure its efficiency.
• Metal (reusable) filters are generally rated MERV 4 and are not normally lab tested.

High efficiency particulate air (HEPA) filters demonstrate at least 99.97% efficiency in trapping 0.3 µm particles, such as microorganisms, smoke fumes, microscopic dust particles and virus carriers. Usually not given a MERV rating, these filters actually exceed the ASHRAE test protocol used to determine MERV ratings. Therefore, these filters are considered as rated above the MERV ratings—or at least “MERV 17” and higher. Applications that would utilize HEPA filters include:

• Hospital surgery rooms
• Medical laboratories
• Manufacturing clean rooms
• Medical device manufacturing
• Semiconductor manufacturing
• Pharmaceutical product processing
• Food processing
• Aerospace
• Multi- and single-family homes

Be aware that higher MERV ratings also equate to higher pressure drops (or more air force needed for the air to penetrate the filter). This can translate to higher HVAC system operating costs. Additionally, be sure the HVAC system is able to tolerate the filter’s MERV rating.

This chart provides an overview of MERV ratings, their efficiencies at trapping these indoor air contaminants and common applications for those ratings’ filters.

No matter what your filtration needs are, The Cary Company has the ideal air filter for your specifications! Browse our selection and find your perfect solution. If you need assistance finding the right filter, please call us at 630.629.6600.