4 Replacement Carbon Booster Filter for Holmes Total Air Purifier Aer1 Series   for Holmes Air Purifier models: HAP2400, HAP242, HAP412, HAP422, HAP424, HAP1200, HAP706 or HAP716. Also fits Bionaire Purifier models BAP260, BAP815, BAP825, BAP1412, BAP1502, BAP1525, BAP1700 and BAP8500. Model AOR31-U Also fits Bionaire Purifier models BAP260, BAP815, BAP825, BAP1412, BAP1502, BAP1525, BAP1700 and BAP8500. Model AOR31-U High Density Carbon Filter Replace at least every 4 months with normal use Easy to install it without cutting any more   Effective air pre-filter removes common household odors, including smoke cooking odors and pet odors, keeps the air in your home clean and fresh   Depending on where it is and how heavy the use is, the pre-filter needs changing every 2-3 months   Package includes: 4 x High Density Carbon Filter