A3501H Bionaire Air Purifier Filters Fits Bionaire models CH3550 and CH3580. Bionaire HEPA air filter cartridge (Superior to hospital grade!) Eliminates 99.97% of all airborne particulate pollutants. A premium filter for cleaner, healthier air. Measures approximately 15 3/4" x 18 3/4" x 4 1/4" For optimum performance, replace filter once every 12 months or as indicated by the Filter Condition Monitor.