Abstract: A method for manufacturing a heat transfer surface and the surface so manufactured. The porous surface is produced by flame spraying a metal substrate with a mixture of metallic and nonmetallic powder particles. The surface is then heated, causing the nonmetallic powder particles to oxidize into gases which diffuse from the surface, leaving voids where the nonmetallic powder particles were located. The voids provide nucleate boiling sites for a liquid being heated by the surface.

Abstract: A water heating module. The module is adapted for heating water for general residential and commercial use and as a supply for a hydronic heating system. The module is capable of supplying a large volume of hot water near instantaneously on demand without exhaustion. There is a small hot water tank in the module, to supply small demands and to reduce ambient losses while module is in standby. Condensing combustion gases are used to preheat incoming cold water; both features combining to produce high fuel efficiency in the module. A radiant infrared burner may be used in the module to eliminate combustion roar and also to substantially reduce NO.sub.x emission, thus enabling sale of the module in jurisdictions having strict NO.sub.x emission standards.

Abstract: A condensing heating module for heating a fluid and adapted for use with a radiant infrared burner. The heat exchanger within the module is spirally disposed about a central burner cavity and has a fluid flow passage of serpentine shape formed within its wall. The upper and lower surfaces of the module, together with the spiral wall of the heat exchanger, form a spiral condensing flue leading from the central burner cavity to an external flue. Those portions of the spiral heat exchanger wall and the module upper and lower surfaces which are exposed to direct radiation from the burner are formed of a corrosion resistant steel, while the remainder of the surfaces and wall are formed of carbon steel to which has been laminated a layer of polypropylene such that the polypropylene layer will be exposed to the flue gas and condensate environment and provide corrosion protection to the carbon steel.

Abstract: A method and apparatus for modulating the surface area of a radiant infrared burner over which combustion occurs as a function of burner heat output rate. This modulation serves to maintain the heat flux density on the surface of the burner at or near an optimum value over a range of heat output rates. The modulation is effected by means of a piston disposed in the internal cavity of a burner which blocks the passage of combustible gas to areas of the burner downstream of the piston from the gas inlet to the burner. The piston is displaced further downstream with increased gas flow rate resulting in combustion occuring over an increased area of the burner surface as burner heat output rate is increased. In its simplest embodiment, the invention comprises a burner oriented vertically with the combustible gas entering the bottom of the burner and a free piston which floats on the incoming gas stream at a level within the burner which is proportional to the gas flow rate.

Abstract: An induced draft warm air furnace employing a radiant infrared burner. The use of a radiant burner results in a very low concentration of oxides of nitrogen (NO.sub.X), in the combustion gases produced. In addition, the use of a radiant burner eliminates the combustion roar produced by other types of burners found in similar furnaces. Further, the invention allows the attainment of the advantages of a radiant burner in a furnace of otherwise standard design with only minor modification. The scope of the invention includes the use of the radiant burner within a combustion chamber which is either within the heat exchanger enclosure and joined to the heat exchanger or within a burner box mounted external to the heat exchanger enclosure but having means for the free passage of combustion gases from the combustion chamber to the heat exchanger. The use of induced draft eliminates the possibility of combustion gases leaking out of the combustion chamber or heat exchanger.