US Patent 7523721 Heat exchanger and water heater

A heat exchanger A1 includes a partition 19 partitioning the space 35 surrounded by a coiled tube 60 at an axially intermediate portion of a housing 2 into a first and a second regions 35a and 35b and partitioning the coiled tube 60 into a first and a second heat exchanging portions HT1 and HT2. The combustion gas supplied to the first region 35a flows to a combustion gas path 36 by passing through a clearance 61 of the first heat exchanging portion HT1 and then passes through a clearance 61 of the second heat exchanging portion HT2. With this structure, the amount of heat recovery is increased, and the heat exchange efficiency is enhanced while simplifying the overall structure of the heat exchanger A1 and reducing the size of the heat exchanger.