Gas-fired water heater with separable heat exchanger or detachably connected external water heater

A gas-fired water heater with an integrated modular air-to-air heat exchange apparatus, said water heater having an insulated tank for storing water to be heated, a combustion chamber under a lower portion with said tank and having a gas burner therein, a flue passageway in said tank and having an outlet end exiting a top wall of said tank, said air-to-air heat exchanger connected to said outlet end and constructed to communicate hot flue gases exiting said outlet end with heat conductive elements in contact with ambient air whereby to extract heat from said hot flue gases and release said heat to said ambient air, said air-to-air heat exchanger being comprised of a flue gas diverting assembly having an inlet chamber with a flue connecting inlet, a plurality of conduits sealingly secured between said inlet chamber and an outlet chamber, a flue connecting outlet secured to said outlet chamber, a plurality of heat sink elements secured to said plurality of conduits to extract heat therefrom, said inlet chamber being a bottom chamber, said flue connecting inlet being located in a bottom wall thereof, said conduits being connected in a top wall of said bottom chamber and extending vertically thereabove, said outlet chamber being spaced above said bottom chamber, said flue connecting outlet being in a top wall of said outlet chamber.