Minimum Efficiency Reporting Values, or MERV, is the primary rating system for an HVAC filter’s ability to capture particles between 0.3 and 10 microns (µm). The higher the rating number, the larger percentage of particles in the air are treated. MERV ratings are from MERV 1 to MERV 20.

Filters with a lower MERV rating, such as MERV 1 to MERV 8, are typically used in residential or light commercial settings, where they effectively capture larger particles like dust and pollen. In contrast, filters with higher ratings, from MERV 13 to MERV 20, are often found in hospitals or cleanrooms, as they can trap much smaller particles, including bacteria, viruses, and even smoke. This makes them critical for environments where maintaining optimal air quality is essential for health and safety.

ASHRAE currently advises the use of filters rated MERV 13 or higher, as these filters effectively capture airborne viruses and other fine particles, while also considering the impact on HVAC system performance.