Abstract: An auxiliary water heating tank to be employed in combination with a conventional tank water heater which is gas fired and supplies heated flue gases to the ambient, the heated flue gases from the water heater to be supplied either into a flue pipe centrally located within the auxiliary heater tank or into a chamber surrounding the auxiliary heater tank, the first embodiment employing a plurality of heat conducting members extending transversely through said flue pipe with the ends of such extending within the auxiliary heater tank, the heating conducting members arranged in a spiral pattern throughout said flue pipe, the members adapted to conduct heat energy from said flue pipe into water contained within said auxiliary heater tank, the second embodiment employing heat sinks and the principle of thermosyphon to efficiently heat the water, the third embodiment conducting the exhaust gases of the water heater into a chamber totally encompassing the auxiliary heater tank.