A minimum-efficiency reporting value, or MERV, rating is helpful for determining whether an air filter traps small allergy-inducing particles, such as dust mites, Home Energy explains. MERV ratings measure how efficiently a filter clears the air of particles of different sizes.
Two main types of particulate matter pollute air quality: coarse particles and fine particles, Air Info Now states. Course particles measure between 2.5 and 10 micrometers, and they include common allergens such as mold and pollen.
Filters with a MERV rating between 1 and 4 are able to trap allergens measuring 10 micrometers or larger, with an efficiency level of at least 70 percent, according to Home Energy. In contrast, a MERV rating of 8 means the filter effectively catches particles as small as 3 micrometers.