| 摘要 |
<P>PROBLEM TO BE SOLVED: To increase the freedom in arrangement of a heat-transfer tube of a sub-heat exchanger for recovering latent heat. <P>SOLUTION: This water heater comprises a second air layer formation tube 46 that is a heat absorption suppressing means suppressing heat absorption in a sub-heat exchange part heat-transfer tube 36 located in an inlet passage 26 between a main heat exchange part 25 and a sub-heat exchange part 27, and an air layer 44 formed between an inner tube 34 and an outer tube 35 in the just under vicinity of a back surface-side fixing plate 38 without expanding the inner pipe 34 of a part extending through the back surface-side fixing plate 38. In the sub-heat exchange part heat-transfer tube 35 located in the inlet passage 26 where a drain water receiver 31 can not be provided below or the back surface-side fixing plate 38 facing the inlet passage 26, heat absorption from exhaust gas can be suppressed to prevent generation of drain water by dew condensation. The freedom of arrangement position of the heat-transfer tube 36 can be increased to increase the freedom in design of the water heater. Consequently, reduction in cost or improvement in heat efficiency can be realized. <P>COPYRIGHT: (C)2007,JPO&INPIT |
