GOODVAC Carbon Odor Prefilters to fit HoMedics AP-15 air purifiers Charcoal prefilters help extend the life of your HEPA filter by catching larger particulates and removing foul odors from the air We suggest replacing the carbon pre-filter every 3-4 months depending on usage and environment. Made to replace HoMedics OEM part number AP-15CRF These filters measure 11" x 11 7/16" x 1/8" GoodVac Replacement for HoMedics AP-15 Carbon Odor Elimating Pre-Filters (4-Pack). Guaranteed to meet or exceed OEM filter performance at a considerably lower cost. We recommend changing these pre-filters every few months to optimize performance and extend the life of the HEPA filter.