Abstract: Turbo ventilator is wind driven conventionally used in industries for proper ventilation. Rotating turbo-ventilators are cost effective environmental friendly natural ventilation devices, which are used to extract polluted air from a building. For its performance testing, test rig is developed in which plenum chamber is act as the room from which stale air is to be thrown outside. Mass flow rate of the turbo ventilator is measured at the suction pipe of the plenum chamber. This paper aims at optimizing the shape and size of plenum chamber to be used during performance testing. From CFD analysis, deviation in differential pressure at different mass flow rate for different volumes is studied in this paper.