The HWF100 filter improves the efficiency of your humidifier by trapping mineral deposits from the water. Is treated with Arm & Hammer baking soda and microban antimicrobial product protection for added peace of mind. Humidifier filters should be replaced at the start of every season and then replaced every 2 to 4 weeks depending on the usage and hardness of the water. The filter works with Bionaire humidifier model No. BCM4600, BCM645, BCM646, BCM5520, BCM5520RC, BCM5521, BCM4600, BCM5520RCU, BCM6000 BCM6010, BCM6010RC, BCM7203, BCM7203RC, BCM7204, BCM7205, BCM7207, BCM7305, BCM7305RCB, BCM7305RC, BCM7306, and BCM7307. It also fit Holmes humidifier model No. HM729, HM729G, HM630, HM7204, HM7305/RC, HM7306, HM6000, HM6000RC, HM6600, HM6005HD, and HM4600/HD.