Winix standard replacement filter for the Winix FresHome P300 air purifier, Plasmawave 5300 air purifier and Winix 6300 air purifier. One-year replacement filter set includes 1 true HEPA filter and 4 carbon pre-filters with antimicrobial coating. Replace as indicated by filter change indicator (approx. every 12 months.) Carbon pre-filters should be changed every 3 months. Filter size 21. Model 21HC4, Item# 115115. Fits Winix models: P300, 6300, 5300, 5000, 9500 and 9000.