Cool-stack III with the height of the cool-stack I and the depth of the cool-stack II, cool-stack III is 1-unit high hot air exhaust system for mid-size racks with mid-size heat loads. With four 120mm fans and an 18-inch depth the cool-stack III can pull up to 70CFM of hot air out of tightly-packed racks while generating very low noise levels. Heated air is normally exhausted through the perforated front panel but exhaust fittings and tubing (provided) can move the hot air safely away to the rear if the rack is located in a closet or cabinet. Cool-stack III is temperature-controlled, switching from a constant, very low idle speed suitable for removing stand-by heat generated by components such as cable boxes and satellite receivers to full speed as rack temperature changes. Temperature is sensed by very small remotely-located thermal switch which uses a strong magnet to secure itself to the component being monitored. Contact closure can also trigger the change to full speed if desired. Internal movable jumpers can be set to satisfy the requirements of a particular installation whether residential or commercial. In an alternate mode of operation the constant-idle is defeated and control is accomplished by 12 volts trigger signal.