Apparatus and system for mixing gas comprising a first valve coupled to a first conduit controlling flow of a first gas, a second valve coupled to a second conduit controlling flow of a second gas, a controller controlling the valves, a base block with a first gas input coupled to the first conduit, a second gas input coupled to the second conduit and an output opening, a mixing chamber formed within the base block, wherein the mixing chamber is coupled to the first gas input and the second gas input to receive input gases, an inner block disposed within the mixing chamber, the inner block including a body with an inner volume and one or more perimeter holes formed through the body coupling the mixing chamber to the inner volume of the inner block; and a gas outlet configured to flow gas through the output opening of the base block.