![](https://www.vaniman.com/wp-content/uploads/2021/07/Pure-Breeze-Calendar-Guide-01.1-683x1024.jpg)
Stage 1 Pre-Filter (P/N 97021): every three months.
Stage 2 Secondary Filter (P/N 97022): every three Pre-Filters (or, every nine months).
Stage 3 Charcoal Odor Filter (P/N 97023): when noticeable odor returns.
Stage 4 HEPA Filter (P/N 97024): every twelve months.