High quality Winix-Compatible carbon filters designed to clean and remove pollutants from your air. Filters should be changed every 3-6 months for optimal performance. Size 21 filter Fits PlasmaWave Series models: WAC5300, WAC5500, WAC6300, 5000, 5000b, 5300, 5500, 6300 & 9000. This is a generic product designed and engineered in the United States by Crucial Vacuum. This is not a Winix OEM product and is not covered under any Winix manufacturer''s warranty. The Winix brand names and logos are the registered trademarks of their respective owners. Any use of the Winix brand name or model designation for this product is made solely for purposes of demonstrating compatibility.