The Minimum Efficiency Reporting Value (MERV) rating for an air filter measures how effectively the filter prevents dust and other contaminants from passing through the filter and reaching the air stream. Filters with higher MERV values trap small particles more effectively than filters with lower MERV scores. The MERV rating scale ranges from 1 to 16, where 1 is the lowest efficiency and 16 describes the highest efficiency. MERV 13-16 filters are capable of trapping 90% or more of particles in the range of 1.0-10.0 microns.
MERV 13 will prevent less than 75% of particles of 0, 3-1 and 0 microns from passing through, MERV 14 will reach up to 84%, MERV 15 up to 94%, and MERV 16 can trap 95% or more of the smaller particles. The particle size range addressed by the MERV scale is 0.3 to 10 microns. The MERV 16 rating is one of the highest possible ratings for air filtration systems. These filters have fibers packed close together, which trap almost as much as a HEPA filter.
The MERV 16 indicates that it can easily remove particles from 0.3 to 1 micron in size. A logical inference is that if an air filter removes particles down to 0.3-10 microns, it is certainly also at least that efficient in removing larger particles. Smoke particles tend to be very small, with a size range close to the wavelength of visible light (0.4-0.7 microns) and, today, MERV 16 filters offer best-in-class performance in that particle size range. The CAL16 and CAL 20 MERV 16 filters were primarily designed for California, but would work just as well in other states where frequent wildfires are a concern. The purpose of the MERV standard is to allow an apple-to-apple comparison of the filtering efficiency of various air filters.
While ASHRAE recommends MERV 13 and 14, it's best to select a filter with the highest possible MERV rating for your specific HVAC system. In general terms, there is a direct correlation between the pressure drop and the MERV rating (the higher the MERV, the greater the pressure drop) when the filters being compared share the same dimensions, depth and fold architecture.
MERV 11
air filters may not trap as many tiny particles as a HEPA filter, but they are cost-effective and work with a variety of types of climate control systems. If your home's air conditioning system is unable to handle the MERV 13, opt for a filter with the next highest possible rating. In fact, an excessive pressure drop is a key reason why traditional filters have a lower MERV limit.MERV 17
to MERV 20 filters are commonly used in surgical operating rooms, clean rooms and other settings that require absolute cleanliness. In general, filters with a MERV 16 rating or lower are considered suitable filters for HVAC systems for residential, commercial and general hospital use.MERV 16 filters are often used in places such as hospitals, where there is a high level of unknown airborne bacteria and viruses that can spread through air ducts. ASHRAE or MERV air filters are tested by testing for dust spots that incorporate fine dust, powdered carbon and some cotton hairs. In reality, the resistance of a filter depends on several factors that are not related to its MERV rating. To sum up, while MERV 11 air filters may not trap as many tiny particles as a HEPA filter, they are cost-effective and work with a variety of types of climate control systems. On the other hand, MERV 16, which offers 95% efficiency in removing particles from 0.3 to 1 micron in size, is one of the highest possible ratings for air filtration systems and is often used in places such as hospitals where there is a high level of unknown airborne bacteria and viruses that can spread through air ducts.