A pedestal is provided for supporting wafer boats in a process chamber during semiconductor fabrication. The pedestal contains hollow spaces, such as within porous insulating plugs, and gases inside the pedestal may expand during semiconductor processing. The pedestal has an opening for exhausting gases out of its interior and into the process chamber. The opening is provided with a filter, in the form of a sintered ceramic or glass disc sealed within a tube covering the opening, to prevent the passage of particles which may be present inside the pedestal. By filtering the particles, the filter removes a source of contamination, thereby allowing for high quality process results on wafers processed in the process chamber.