A high efficiency downfired gas water heater is provided which has a tank for storing water to be heated, a combustion chamber extending downwardly through a top end of the tank, and a gas burner operative to create hot combustion products within the combustion chamber. At the bottom end of the tank is a transfer chamber coupled to an external discharge conduit and to a single pass heat exchanger, in the form of multiple flue tubes. extending vertically through the tank and connected to the combustion chamber. In one embodiment of the water heater the burner is a power burner which forces the combustion products sequentially through the combustion chamber, heat exchanger, transfer chamber and discharge conduit. In another embodiment of the water heater a draft inducer fan is used to draw the combustion products through this path from the combustion chamber.

A supercritical steam generator includes a downdraft furnace enclosure, a hopper tunnel, and a convection pass enclosure, with the hopper tunnel joining the downdraft furnace enclosure and convection pass enclosure together. Flue gas passes down through the downdraft furnace enclosure through the hopper tunnel and up through the convection pass enclosure. This structure permits the outlet steam terminals, which provide access to the resultant supercritical steam and/or reheat steam, to be located at a base of the steam generator rather than at the top of the steam generator as with conventional boilers. This reduces the length of the steam leads from the steam generator to a steam turbine that produces electricity using the supercritical steam.

A high efficiency downfired gas water heater is provided which has a tank for storing water to be heated, a combustion chamber extending downwardly through a top end of the tank, and a gas burner operative to create hot combustion products within the combustion chamber. At the bottom end of the tank is a transfer chamber coupled to an external discharge conduit and to a single pass heat exchanger, in the form of multiple flue tubes. extending vertically through the tank and connected to the combustion chamber. In one embodiment of the water heater the burner is a power burner which forces the combustion products sequentially through the combustion chamber, heat exchanger, transfer chamber and discharge conduit. In another embodiment of the water heater a draft inducer fan is used to draw the combustion products through this path from the combustion chamber.

A high efficiency downfired gas water heater is provided which has a tank for storing water to be heated, a combustion chamber extending downwardly through a top end of the tank, and a gas burner operative to create hot combustion products within the combustion chamber. At the bottom end of the tank is a transfer chamber coupled to an external discharge conduit and to a single pass heat exchanger, in the form of multiple flue tubes. extending vertically through the tank and connected to the combustion chamber. In one embodiment of the water heater the burner is a power burner which forces the combustion products sequentially through the combustion chamber, heat exchanger, transfer chamber and discharge conduit. In another embodiment of the water heater a draft inducer fan is used to draw the combustion products through this path from the combustion chamber.

A plate-shaped heat insulator including a plate-shaped papermaking product containing inorganic fibers, and one or more grooves in at least one of its surfaces. The plate-shaped heat insulator is intended to be disposed in a combustion chamber.