A water heater system includes a primary heat exchanger including a tank and at least one flue, and a secondary heat exchanger including a core and a flue gas flow path. The water heater is operable in a heating mode in which a combustor produces hot flue gas and a water pump flows water through the core of the secondary heat exchanger and into the tank, and in a non-heating mode in which the combustor and the water pump are inoperative. The flue gas flows from the combustor through the at least one flue to heat the water in the tank and then through the flue gas flow path to heat water in the core before being exhausted.

An evaporator with integrated heat recovery incorporates a vapor tube in a combustion chamber surrounded by a water jacket. The water jacket is in fluid communication with an exhaust gas heat exchanger. Coolant circulates in series or parallel first and second coolant flows through the exhaust gas heat exchanger to recover heat from exhaust gasses leaving the combustion chamber and through the water jacket surrounding the combustion chamber to recover heat not delivered to the operating fluid. The evaporator may incorporate a condenser within the housing and in fluid communication with the exhaust gas heat exchanger and/or water jacket. The evaporator may be divided to flow in parallel through the condenser the exhaust gas heat exchanger. The water jacket may be fluidly connected with one or the other of the condenser or the exhaust gas heat exchanger.

A hot-water boiler with an incline type firebox is proposed. In the hot-water boiler, a fire tube connector of the firebox is inclined to be deeper from an end of a firebox side to a central portion thereof, thus reducing vortices that may be generated by hot air and flames supplied from a burner.

A fluid heating system including: a pressure vessel; an assembly comprising: a heat exchanger core including a second inlet and a second outlet; a first conduit having a first end connected to the second inlet of the heat exchanger core and a second end disposed outside of the pressure vessel; a second conduit having a first end connected to the second outlet of the heat exchanger core and a second end disposed outside of the pressure vessel; and a blower in fluid connection with the first end of the first conduit, wherein the fluid heating system satisfies the condition that a Bulk Heat Flux between the first end of the first conduit and the first end of the second conduit is between 45 kW/m.sup.2 and 300 kW/m.sup.2, and wherein the Pressure Drop between the first conduit and the second conduit is between 3 kiloPascals and 30 kiloPascals.

A tube sheet for a thermal transfer device can include a body having a plurality of apertures that traverse therethrough, where the plurality of apertures are configured to receive a plurality of tubes of the thermal transfer device. The tube sheet can also include an outer perimeter defining the body, where the outer perimeter has at least one first recess feature disposed therein. The at least one first recess feature can have a first shape and a first size, where the first shape is any shape aside from a semi-circle.

A heating device has a combustion chamber and a gas flue configured to guide hot exhaust gas generated in the combustion chamber, the flue having an inlet region and an outlet region and is configured connected to the combustion chamber via the inlet region. Heat transfer ribs having a wall thickness are arranged spaced from each other in the gas flue for the heat transfer from hot exhaust gas to the gas flue. The wall thickness of the heat transfer ribs and/or the distances of the heat transfer ribs to one another are optionally configured to be larger on the sides of the inlet region than on the sides of the outlet region.

The disclosed technology includes a fluid heating device including a frustoconical combustion chamber and a heat exchanger that can include heating tubes. The combustion chamber can have a first end and a second end that is in fluid communication with the heating tubes. The surface area of the second end of the combustion chamber can be larger than the surface area of the first end of the combustion chamber.

A fluid heating system assembly includes a first tube sheet, a second tube sheet opposite the first sheet, a plurality heat exchanger tubes, which connect the first tube sheet and the second tube sheet, and a plurality of baffles, comprising at least one plate baffle and at least one annular baffle disposed between the first tube sheet and the second tube sheet, wherein the heat exchanger tubes sealingly pass through the baffles, and wherein the tubes are arranged in a staggered ring configuration and the baffles have a baffle spacing, such that there is a substantially uniform temperature distribution and efficient exchange of thermal energy across the heat exchanger tube walls.

A tube for a thermal transfer device can include at least one wall having an inner surface and an outer surface, where the inner surface forms a cavity. The inner surface can be non-cylindrical. The cavity can be configured to receive a fluid that flows continuously along a length of the at least one wall.

A fluid heating system for heating a production fluid using a thermal transfer fluid, the production fluid being contained in a vessel includes an electric blower configured to receive ambient air and electrical input power and to provide output source air, a combustion system configured to receive the source air from the electric blower and to receive fuel and to provide the thermal transfer fluid, a heat exchanger configured to receive the thermal transfer fluid from the combustion system and configured to provide heat exchange from the thermal transfer fluid to the production fluid, and to provide output exhaust gas, and wherein the electric fan provides a predetermined volume flow rate of the output source air at a predetermined blower efficiency such that the fluid heating system has a Bulk Heat Flux of at least about 14.7 kBTU/Hr/ft.sup.2 and a Pressure Drop of at least about 0.7 psi.