Liquid heating apparatus

A liquid heating apparatus comprising:

• a liquid bath;
• a combustion chamber provided with a burner, said combustion chamber being positioned on a side on a lower portion of the liquid bath;
• and at least one exhaust pipe located in and passing through the liquid bath in a substantially horizontal state extending from one side of the liquid bath toward the other side thereof in order to heat a liquid in the liquid bath, at least one exhaust pipe receiving a combustion gas generated in the combustion chamber, said combustion gas passing through the exhaust pipe, said at least one exhaust pipe end exiting said combustion gas to ambient, said exhaust pipe being formed into a generally tubular shape having at least one vertical side wall, said exhaust pipe being separate from and downstream of both said combustion chamber and said burner;
• and a fin fixedly located on and extending from an inner surface of said side wall of said exhaust pipe along a longitudinal direction thereon, said fin defining longitudinal passageways from shorter to longer such that said longitudinal passageways merge with one another at a tip on the extending fin at a point furthest away from said burner, said fin tip directing low temperature combustion gas, which has performed a thermal exchange with said fin heating said fin, into a merged passage formed by the passageways, additional high temperature combustion gas flowing along said longitudinal merged passage contacts said longitudinal fin downstream of said low temperature combustion gas, said additional high temperature combustion gas heating a downstream fin and providing substantially uniform heat exchange in the longitudinal direction.