Standards and guidelines for air filter efficiency have been around for several decades, but the standards have continually evolved over time. This has caused some confusion within the industry, especially for contractors.
ANSI/ASHRAE Standard 52, issued originally in 1968, was one of the first formal standards to address the testing of air filter efficiency. This standard was updated to 52.1 in 1992. It also led to the creation of ANSI/ASHRAE Standard 52.2, “Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size.” The standard was meant to address new filtration concerns and improve some outdated practices of the previous standard, but Standard 52.1 is still valuable, at least for the time being.