Abstract: A hot-air furnace has a long-flame burner for combusting gas or liquid fuel with a combustion chamber connected to the burner and having its length (l) and width (w.sub.1) in relationship of w.sub.1 <l. A heat exchanger is located above the combustion chamber and has internally a gas flow guide plate which guides combustion gas flow discharged from the combustion chamber to the heat exchanger. The heat exchanger has a width (w.sub.2) and length (l) in the relationship of w.sub.2 <l. An exhaust port for exhausting the combustion gas flow is located at the front or rear of, right or left-hand side of or on the top side above said heat exchanger. A casing has a drum integrally connecting the combustion chamber and the heat exchanger, an air flow guide and directing plate which covers the drum, a radiant heat absorber plate outside the combustion chamber, and a blower above or below the drum.

Abstract: A heat exchange apparatus which utilizes the solar heat, hot spring water or underground water comprises a cylindrical main body, an internal cylinder placed in the main body, a blower provided in an upper part of the internal cylinder, an air intake, a number of radially arranged air exhaust tubes, ring shaped upper and lower heat exchange compartments, and chambers formed between heat exchange compartments, on and under the upper and lower heat exchange compartment, upper and lower chambers are connected by coil tubes placed in heat exchange compartments, the outer coil tubes and inner coil tubes are successively connected so that each of connected coil tubes has the same overall length, which improves efficiency of heat exchange between air and water which are caused to move in a counterflow fashion.

Abstract: A heat exchange apparatus which utilizes the solar heat, hot spring water or underground water comprises a cylindrical main body, an internal cylinder placed in the main body, a blower provided in an upper part of the internal cylinder, an air intake, a number of radially arranged air exhaust tubes, ring shaped upper and lower heat exchange compartments, and chambers formed between heat exchange compartments, on and under the upper and lower heat exchange compartment, upper and lower chambers are connected by coil tubes placed in heat exchange compartments, the outer coil tubes and inner coil tubes are successively connected so that each of connected coil tubes has the same overall length, which improves efficiency of heat exchange between air and water which are caused to move in a counterflow fashion.