ideal.’s replacement filter cartridge for the ideal. AP15 Classic air purifier arrives in a single, easy-to-install cassette, which simply snaps into the air purifier body. The cassette is coated with a CleanCel antimicrobial additive, and contains a true HEPA fine dust filter and activated carbon filter, all in one cartridge. The filters provide 99.97% filtration efficiency for particles as small as 0.3 microns, including bacteria and viruses, through a five-level filtration system. Each AP15 Classic air purifier comes with a washable pre-filter, which is a permanent filter and not included with replacement cassettes. Cassettes should be replaced every 12 months with average use, and the washable prefilter should be vacuumed and rinsed every 2 weeks to maximize the life of all filters.