Apparatus and methods for depositing a film in a PECVD chamber while simultaneously flowing a purge gas from beneath a substrate support are provided herein. In embodiments disclosed herein, a combined gas exhaust volume circumferentially disposed about the substrate support, below a first volume and above a second volume, draws processing gases from the first volume down over an edge of a first surface of the substrate support and simultaneously draws purge gases from the second volume upward over an edge of a second surface of the substrate support. The gases are than evacuated from the combined exhaust volume through an exhaust port fluidly coupled to a vacuum source.