Tier1 Replacement for Lennox 20x21x5 Merv 13 Air Filter 2 Pack Upgraded media rated at MERV 13 to capture 90% of particles, 1 microns or smaller in size Replacement for: Lennox X8790 This product is listed and rated by Underwriters Laboratories as U.L. Class 2 This product is listed and rated by Underwriters Laboratories as U.L. Class 2