Abstract: A waste heat reclaimer takes in hot waste gases from stacks or flues, associates them with a primary flow of water, heating the water and cooling the gases. The heated water flows through a heat exchanger transferring that heat to a secondary flow of water. A logic and control unit receives signals from sensors located in the sources of the waste gases, the delivery system of the gases, and the two flows of water. These signals are used to give warnings of insufficient flows, insufficient heat energy gains, and to control the sources of the gases, and to provide the operator with other indications which permit him to obtain more efficiency from the unit while devoting less attention to it.