Winflo carbon filters/charcoal filters with 2-pieces set is designed for select Winflo range hoods ductless installation. Please see the manufacturer sticker on the range hood to ensure the fit before purchase. They are attached to the range hood blower to clean the air before recirculating back into the house. Duct work to the outside isn't necessary. Winflo carbon filters are the solution for kitchens that don't have an exhausting duct option. This carbon filter fits some (not all) Winflo wall mount and island mount range hoods.