Filters with higher MERV ratings are more effective in trapping small particles than those with lower ratings. Generally, filters with a MERV 16 rating or lower are considered HVAC system grade filters for residential, commercial, and general hospital use. MERV, also known as the Minimum Efficiency Report Value, is a scale that rates the effectiveness of filters in capturing particles in the air. This scale ranges from 1 to 16, with 16 being the most efficient. The CAL16 and CAL 20 MERV 16 filters were designed mainly for California, but they can be used in other states where wildfires are common.
We will also look at the MERV rating an air purifier should have to filter different air pollutants (pollen, mold spores, smoke, dust, etc.). AprilAire MERV 16 filters can eliminate up to 99%* of allergy and asthma triggers, such as smoke, pollen, mold and more. To be classified as MERV 8 by NAFA, a filter must remove at least 70 percent of particles 3 to 10 microns in size and 20 percent of particles 1 to 3 microns. Since they go beyond the MERV table, they are known as HEPA filters or high-efficiency filters. HEPA filters are 99.97% efficient at capturing particles with a diameter of 0.3 microns, while most MERV 16 filters offer efficiencies of approximately 95%.
As for CO and ozone, the MERV rating of a filter is irrelevant since filtering these pollutants requires a different strategy. In general terms, there is a direct correlation between pressure drop and MERV rating (the higher the MERV, the greater the pressure drop) when the filters being compared have the same dimensions, depth and pleat architecture. But how do you know if the air you breathe is filtered properly? An important measure of air filtration is what is called the minimum efficiency report value or MERV level of the air filter through which the air moves. In reality, the resistance of a filter depends on several factors that are not related to its MERV rating. Although it may seem like you should strive to have air filters with a MERV value of 20 that protect every space, this is not always recommended for several reasons.
Improper use of a MERV 16 filter can greatly reduce the life of your unit and result in additional maintenance costs. In essence, the MERV classification gives us an idea of how filters (air purifiers, ovens) can filter particles from 0.3 to 10 microns (10-6 m). Ultimately, a dirty filter will have the same impact on an HVAC system as using a filter with a MERV level that is too high for the equipment. Before buying a MERV 16 rated air filter, make sure your unit is designed to withstand this level of filtration.