All about MERV ratings

Every furnace filter has a Minimum Efficiency Reporting Value (MERV) rating, which measures how efficiently the filter captures particles of specific sizes that pass through it as your furnace operates. MERV ratings range from 1 (least efficient) to 16 (extremely efficient). Particles are measured in microns and range from carpet and textile fibers (greater than 10 microns) to microscopic bacteria (less than 0.3 microns).

To determine MERV ratings, air filters are put through two primary tests: The Dust Spot Efficiency Test, which measures the ability of the filter to remove atmospheric dust particles from the air, and the Arrestance Test, which measures the filter's ability to remove synthetic particles that have been injected into the air for testing purposes. Most high-quality filters can remove 90% or more of injected particles from the air in the Arrestance test (in other words, they do a good job of removing what they're expected to). Because atmospheric dust applies equally to all filters, Dust Spot Efficiency varies widely.

To put it into real-world terms, a MERV rating of 1 would be a basic window air conditioning unit -- it filters large particles but isn't meant to clean the air. A 16 is suitable for a hospital surgical environment, with an extremely high level of filtration that isn't necessary for the vast majority of residential homes.

Most residential air filters have a MERV rating of 1 - 4, which on the high end filters out pollen, dust mites, and fibers. These filters are generally disposable panel-type filters that are inexpensive but don't do an adequate job of filtering particles smaller than 10 microns, including mold spores, pet dander and aerosol spray. We offer several grades of filters:

• MERV 8 air filters
• MERV 11 air filters
• MERV 13 air filters

These filters meet the needs of virtually all homes, providing clean, health air, and protecting your HVAC equipment.

When it comes to choosing a residential furnace filter, it's best to factor in your household's health needs, the environment (including pets and other potential indoor pollutants), and your budget. While it's generally true that the higher the MERV rating, the higher the quality, the highest-rated filter isn't necessarily the best choice for all homes. Families with certain health conditions and allergies can benefit from a filter with a MERV rating of 11 or 13, while others can enjoy both affordability and efficiency by choosing 8.