Abstract: A plurality of rows of circular openings for supporting water tube sections and turbulence fin arrays comprising plural vertically arrayed fin slots for guiding combustion gas to flow upwards at an angle therethrough are provided on each of a plurality of fin plates which are arrayed in parallel and disposed at the upper end of a water heater. The circular openings and the turbulence fin arrays of each row are alternately positioned. Therefore, each circular opening of a lower row is located below either of the turbulence fin arrays of a next higher row and each turbulence fin array of a lower row is located below either of said circular openings of a next higher row.