A paint spray booth (10) has a spray chamber (11), an air make-up unit (15), and an air exhaust system with an exhaust air fan (26) and an exhaust damper (25). The booth has a pressure transducer (29) that senses the pressure of air both inside and outside the booth and which transmits control signals indicative of sensed changes in the differential air pressure to motors that drive the exhaust fan or the exhaust damper. In this manner the exhaust air flow rate is adjusted to compensate for changes in the differential air pressure.