| 摘要 |
PROBLEM TO BE SOLVED: To reduce the drain in a heat exchanger and to make an appliance slim. SOLUTION: Cold water introduced from a feed water pipe 17 is led to a subordinate heat transfer tube 8a provided as a subordinate heat exchanger 8, and it is heated by combustion gas passing through a main heat exchanger 7 and led to a wound pipe 20. Then, it is led from the wound pipe 20 to a main heat transfer tube 7a of the main heat exchanger 7, heated further therein and let out from a hot water outlet pipe 18. Since the water introduced into the wound pipe 20 is preheated in the subordinate heat exchanger 8, the drain on the inner wall surface of a combustion chamber 5 can be reduced. Since a space between the inner wall surface and a burner can be lessened, the appliance can be made smaller in size. Since the hot water of high temperature is passed through the main heat exchanger 7, the drain therein can be reduced effectively. |
