HEAT EXCHANGER

PROBLEM TO BE SOLVED: To absorb combustion heat uniformly and improve the durability of a heat exchanger by designing sizes of a plurality of water tubes from the lower end of a heat absorbing fin so as to be different from each other respectively, in a heat exchanger, in which a plurality of rows of water tubes are penetrated through the group of heat absorbing fins and water in the water tubes is heated by heat from the lower part of the heat absorbing fins. SOLUTION: A one boiler two circuits type hot-water supplier is provided with a multitude of fins 2, constituting the group of heat absorbing fins, and a pair of upper and lower water tubes 5 while a plurality of rows of water tubes 5 are penetrated through the group of heat absorbing fins to absorb heat by the flow of water and the arrangement of the pipelines of upper and lower stages are arbitrary such as zigzag and the like. In this case, the size L from the lower end of a fin 2 to a water tube 4 of the side of lower stage is specified so that the size at the side of end of the fin is made larger than the other sizes. On the other hand, heat shielding ports 22 are bored around the upper and lower heat absorbing tubes and a stepped part 23 is arranged to change the directional property of combustion gas. According to this method, the absorbing amount of heat at the side of the low stage is equalized to facilitate the control of the absorbing amount of heat and prevent bumping due to excessive absorption of heat in a specified part whereby the durability of the heat exchanger is improved.