Abstract: A ventilation system includes one or more exhaust fans and one or more make up air fans. Each fan has is driven by a motor operating at a constant speed. Each fan and motor are coupled by a torque converter, so that the torque applied to the fan is constant. Exhaust fan speed varies according to the ideal gas law, whereby the fan speed automatically varies in response to changes in system conditions, such as temperature and the associated changes in air density and resistance to the fan.