Abstract: A ventilation system for use, in example, on a spray booth or paint stripping enclosure, in which variable speed fans (or equivalent) are employed, and controlled by a sensor so that the flow rate exhausted from the booth (and directed either to an emission control device or vented to atmosphere) is continually adjusted to minimize the exhaust flow rate from the enclosure. The remainder of the ventilation air is recirculated back into the enclosure. An analyzer located in the recirculation duct continuously monitors the concentration of hazardous constituents present in the recirculation stream, and transmits this data to a central controller, which controls the ventilation fan systems. The central controller controls the recirculation duct and exhaust duct fan systems to achieve the highest recirculation rate possible, yet also maintain constituent concentrations in the recirculation duct at a safe level.