A tracer gas technique based on ASTM Standard E741-83 was used to measure ventilation performances in a model chamber ($0.84m{ imes}0.68m{ imes}0.7m$) with an exhaust fan and a supply fan. Experiments were performed for the ventilation effectiveness on three types of mechanical ventilation systems. For all cases. higher ventilation effectiveness was found in the type to ventilation system due to shorter residual time of air compared to type 1 and type 3.