The Brother FH221 High-Efficiency Filter is designed for use with the AirSure DF-2 Dynamic Filtration Air filtration system. This High-Efficiency filter helps clear the air by capturing airborne particles as small as 0.3 microns and helps reduce allergens and minimize pollutants in your immediate space in tandem with the air filtration system. It's easy to replace your Brother Genuine High-Efficiency filter FH221. Replacing every 550 hours or three months is recommended.