Abstract: This invention teaches an improved exhaust system to be used with a paint spray booth and having a continuously operating power exhaust fan. The exhaust system has a damper that is opened when spraying actively is taking place in the spray booth and that is closed when there is no spraying actively taking place in the spray booth. A control switch is mounted in any of several locations to determine when the spray gun is in use or is not in use. Thus, the control switch is actuated when the spray gun is hung up . . . indicating a nonuse condition of the spray system; whereupon use of the spray gun lifts the gun from the hook to indicate spraying activity. A motor drives the damper to the opened position; and a spring biases the damper to the closed position. A timer is also used to delay the closing of the damper until between twenty and possibly two hundred seconds have lapsed after spraying activity has terminated.