Submersible high-efficiency combustion chamber for a water heater

An apparatus for heating water in a water tank comprising:

• a first tubular member having a closed back end;
• a second tubular member having a longitudinal axis, an input end and an exhaust end, said second tubular member disposed and supported at least in part within said first tubular member to form an annular clearance space therebetween, said exhaust end spaced apart from said closed end of said first tubular member;
• a plurality of longitudinally extending fins supporting said second tubular member within said first tubular member, said fins disposed circumferentially about the exterior surface of the second tubular member, said fins each having a length substantially parallel to the longitudinal axis;
• a plurality of baffles for turbulating combustion gases, each of said baffles being slidably positioned between a pair of adjacent fins and spaced therefrom such that said baffles are replaceable without removing the first tubular member from the water tank, said baffles defining with said fins and the interior surface of the first tubular member a series of axially extending passageways that can be traversed by the combustion gases;
• a burner coupled to the input end of the second tubular member for supplying the combustion gases to the interior of the second tubular member;
• and
• means for collecting the combustion gases after the combustion gases traverse said annular clearance space.