The rear door heat exchanger is a water-cooled device that mounts on the rear of the IBM 19-inch and 24-inch racks to cool the air that is heated and exhausted by devices inside the rack. A supply hose delivers chilled, conditioned water to the heat exchanger. A return hose delivers warmed water back to the water pump or chiller. Each rear door heat exchanger can remove up to 50 000 BTU (or approximately 15 000 watts) of heat from your data center.