Winix standard replacement filter for the Winix FresHome P450 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 25. Model 25HC4, Item# 113250. Fits Winix models: P450.