Abstract: A high efficiency hot air furnace transfers substantially all of the combustion heat of a clean fuel gas fire to a stream of cool recirculating air by two heat exchangers both of which are mounted in a common plenum through which cool air is recirculated by means of a blower. It differs from the conventional high efficiency furnace in that the secondary heat exchanger is a porous movable heat sink which is alternately exposed to a stream of hot combustion gas and a part of the cool air stream from the recirculating air blower.

Abstract: The humidity of a heated space is regulated by varying the amount of moisture transferred from the combustion gases of the furnace used to heat the space. A porous heat sink element is arranged to move through the path of the combustion gases and one or more reclaim-air paths. The heat sink member can take any of a variety of forms; it can reciprocate back and forth along a track, or it can be configured as a rotating wheel ("heat wheel"). The amount of moisture transferred from the combustion gases to the reclaim air is governed by a humidity signal. If the humidity signal calls for a change in humidity, one of several parameters is varied to provide for a greater or lesser transfer of moisture from the combustion gases to the reclaim air.

Abstract: Substantially all available heat from a combustion gas stream is extracted by passing it through a cool, porous heat sink, which is thereby heated, and then releasing that heat into a cool air stream blown through the same porous heat sink in a second step (preferably in the opposite flow direction). The heat sink absorbs substantially all the available heat of combustion rather than merely scavenging what would otherwise be stack losses. The invention provides an improved means of recovering virtually all the available heat produced by combustion of a fuel gas. It permits recovery of the heat lost in a conventional single-zone furnace. The improved heat recovery is achieved without contamination of the ambient air with exhaust gas residues as occurs in direct-fired systems, and without incurring the problems of corrosion and waste disposal inherent in two-zone indirectly-fired systems.

Abstract: A heat exchanger for reclaiming energy from an exhaust airstream. The exchanger includes a porous metal element suitable for absorbing heat from the exhaust airstream, means for reciprocally moving the porous element back and forth transversely to the exhaust airstream, an inlet duct for receiving the exhaust airstream and directing it through the porous element to an outlet duct, and reclaiming air blower means for delivering two heat-reclaiming airstreams through the porous metal element, one on either side of the exhaust airstream, and an air exhaust fan in the path of said exhaust airstream for drawing said airstream through said porous element.