Air filters have two purposes. The first is to protect your HVAC system and thereby your investment. An HVAC system is one of the biggest investments you can make in your home. Most people purchase a new HVAC only once every 15-20 years. The second is to provide good indoor air quality. Filters do this by removing small particulate matter from the air that you breathe.
There are different types of air filters, rated by how well they remove very small particles measured in micrometers. The MERV rating stands for Minimum Efficiency Reporting Values, and measures filter effectiveness at removing particles from .3 to 10 micrometers. The MERV scale is from 1 – 16. For reference, particles at 10 micrometers include things like cockroach debris and pollen (MERV 1-4). 3 to 10-micrometer particles include pet dander and mold spores (MERV 5-8). 1 to 3-micrometer particles include lead dust and auto emissions (MERV 9-12). Particles at .3 to 1 micrometer include bacteria and respiratory droplets (MERV 13-16). A 16 is the highest possible MERV rating and is the quality of air filter used in hospital surgeries.