The Rheem-Ruud RXGW-B01 Chimney Adapter is an OEM venting accessory designed for compatible upflow, Category I, fan-assisted 80% gas furnaces. It connects the furnace flue outlet to an approved chimney venting system, helping safely direct combustion gases outdoors. Designed for use with select Rheem and Ruud furnace models, this adapter is particularly suitable for tile-lined masonry... https://www.partshnc.com/rxgw-b01-rheem-ruud-chimney-adapter