MERV 8 filters are 90 percent efficient on particles that are 3 to 10 microns in size. To be classified as a Merv 8 filter by the NAFA (National Air Filtration Association), a filter must filter at least 70% of E3 particles (3.0-10.0 µm) and 20% of E2 particles (1.0-3.0 µm). In addition to 70% of E3 particles, it also filters 30% of E2 particles and 1.9% of E1 particles (0.3-1.0 µm). This means that 81.5% of the dust particles introduced into the filter were successfully filtered out of the air.
A MERV 8 filter is considered a superior filtration compared to air filters with a lower MERV rating, and is commonly used in homes, commercial buildings, paint booths, and industrial workplaces. It is not designed to trap the smallest particles that fall into category E1, such as pet dander. In many cases, a MERV 8 air filter is more than adequate for controlling larger particles, such as sanding dust, spray paint dust, lint and carpet fibers. However, if you are concerned about outdoor air pollution, family members with respiratory problems, or pets in the house, then a higher merv rating might be a good idea.
A MERV 11 air filter is slightly more expensive than a standard filter, but paying a few dollars more per filter is generally worth the extra efficiency. Using the filter with the highest Merv rating in your home would restrict that airflow, making it difficult for your HVAC to function properly. If someone has an allergy or respiratory problem, choose a MERV 11 air filter or even a MERV 13 air filter. Generally speaking, anything under a MERV 13 air filter should provide very efficient air purification in a home without affecting airflow.