Holmes Aer1 Full Season 4-Filter Kit Contains: 2 HEPA-type Total Air filters, 1 True HEPA Allergen Remover Filter, 1 Odor Eliminator Filter For best performance, change Total Air and Odor Eliminator Filters every 4 months For best performance, change True HEPA Allergen Remover Filter every 12 months Compatible with all Holmes and Bionaire aer1 ready Air Purifiers