Embodiments described herein relate to a base ring assembly for use in a substrate processing chamber. In one embodiment, the base ring assembly comprises a ring body sized to be received within an inner circumference of the substrate processing chamber, the ring body comprising a loading port for passage of the substrate, a gas inlet, and a gas outlet, wherein the gas inlet and the gas outlet are disposed at opposing ends of the ring body, and an upper ring configured to dispose on a top surface of the ring body, and a lower ring configured to dispose on a bottom surface of the ring body, wherein the upper ring, the lower ring, and the ring body, once assembled, are generally concentric or coaxial.