The Winix Air Purifier Prefilter 21C4 includes Genuine Winix one year replacement filter set. These filters can capture vapors and odors within the air. 4 Washable Pre-Filter's True-HEPA filtration Washable AOC Carbon filter For optimal performance, it is recommended to replace the carbon filters every 3 months. This is a Replacement Filter Kit for the Winix Air Purifier unit 5500.