A complete Atmospheric Controller makes it easy to coordinate CO2 and vent cycles. The controller has one dual-outlet on its left side for the CO2 device and another dual outlet on the right side for exhaust fans. Whenever temperature or humidity rises above the level you select, the Atmospheric Controller activates the exhaust and shuts off the CO2. The aluminum case mounts directly on the wall. This model has a Photo Sensor to limit CO2 generation to daytime cycles only. model CT-DH-3P