A gas delivery system for supplying a process gas from a gas supply to a thermal processing furnace, a thermal processing furnace equipped with the gas delivery system, and methods for delivering process gas to a thermal processing furnace. The gas delivery system comprises a plurality of regulators, such as mass flow controllers, in a process gas manifold coupling a gas supply with a thermal processing furnace. The regulators establish a corresponding plurality of flows of a process gas at a plurality of flow rates communicated by the process gas manifold to the thermal processing furnace. The gas delivery system may be a component of the thermal processing furnace that further includes a liner that surrounds a processing space inside the thermal processing furnace.