The MDVS, Mechanical Dryer Venting System™ is a demand controlled ventilation system designed specifically for multi-story buildings that have clothes dryers on multiple floors or in a central laundry facility. Unlike traditional exhaust systems that operate at full speed 24/7, the demand-controlled ventilation system senses when no appliances are running and operates at a very low speed. Once the appliance starts, the internal appliance fan creates pressure inside the duct which make the control increase fan speed.