The present invention provides a heat treating process chamber (200) having a housing (203) with a flow passage (201) in communication with a vestibule assembly (222a, 222b). The vestibule assembly includes an outer ring (218) with a first groove (224) and an inner ring (220) with a second groove (230). The first groove is formed in an axially inwardly facing surface of the outer ring. The first groove has a portion open in a radially outer direction and an axially inner direction. The second groove opens in an axially inner direction and is formed in an axially outwardly facing surface of the inner ring. The first and second grooves form a passageway when they are in an axially superimposed relationship. The first groove forms a radially outwardly open end and the second groove forms an axially inwardly facing end of the passageway. The passageway communicates with the flow passage thereby allowing passage of a temperature adjusting medium.
