HQRP Filter 3-pack for Honeywell HCM-500 Series HCM-530 HCM-535 HCM-540 HCM-550 HCM-560 HCM-551 Humidifier + HQRP Coaster HQRP&reg; 3-pack Humidifier Filter Replacement plus HQRP&reg; Coaster; Filter Helps To Capture Mineral Deposits And Improve Efficiency Of The Humidifier; For Maximum Performance Change Filter Every 30 Days; 2 weeks DOA replacement warranty!