MERV Ratings: Decoding Air Filter Quality

All filters are subject to a MERV rating, including Honeywell and 3M furnace filters. The effect your filter has on the air quality on your home or office depends on this rating. To give you an idea of what each rating means tangibly, examples are given at what can effectively be collected from the air:

• A filter with a MERV rating between 1 and 4 can trap up to 20% of particles between 3-10 microns in size, depending on the specific rating. This includes pollen, dust mites, standing dust, spray paint dust, cockroach debris and carpet fibers.  These are commonly used in window AC units.
• A filter with a MERV rating between 5 and 8 captures between 20-85% of particles 3-10 microns in size, depending on the specific rating. This includes mold, spores, cat and dog dander, dusting aids, pudding mix, hair spray, fabric protector and cement dust. These are used for higher quality residential units, commercial units, and industrial areas.
• A filter with a MERV rating between 9 and 12 captures between 50%-89% of particles 1-3 microns in size, and at least 85% of particles 3-10 microns in size, depending on the specific rating. This includes humidifier dust, lead dust, Legionella, nebulizer droplets, auto emissions and milled flour. These are the best residential filters you can buy, and are commonly used in hospitals, superior commercial environments and laboratories.
• A filter with a MERV rating between 13 and 16 captures at least 75% of particles 0.3-1.0 microns in size, at least 90% of particles 1-10 microns in size, depending on the specific rating. This includes bacteria, most tobacco, cooking oil, most smoke, insecticide dust, most face powder, most paint pigments and sneeze particles. These are used in hospitals and general surgery rooms.
• A filter with a MERV rating between 17-20 captures particles smaller than 0.3 microns in size. This includes viruses, carbon dust, sea salt and smoke. These are used in electronics and pharmaceutical manufacturing clean rooms.

Filters come in a variety of qualities. Generally, an electrostatic furnace filter is the highest quality you can find. Unlike a cheap fiberglass filter, electrostatic technology actually pulls particles out of the air. So instead of relying on the density of fibers to collect particles, it relies on their electromagnetic charge. Only relying on fiber density makes it impossible to collect key allergens. Electrostatic fiber layers have different charges. As a particles pass through the layers of an electrostatic filter, they are attracted to the layer that is opposite of its charge. This, in turn, forces the particle to stick to the filter until it is cleaned.

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