HF2 Replacement Filters are designed for use with Black+Decker 1.45 Gallon Ultrasonic Humidifiers. It is recommended to replace your Cool Mist Humidifier filter every 6 months. Replacement filters are sold in packs of 2 to provide up to 1 year of clean moisture. Ceramic infused filter softens water and reduces calcium build up to deliver healthy air moisture. Washable for easy set up and cleaning. Each filter measures 2.8"" diameter x 3.74"" L.