PURPOSE: To improve a thermal efficiency in a complex hot water heater for bath tube heated by gas or the like by a method wherein an output for a forced water feeding heat exchanger is branched, a hot water feeding pipe is opened at a natrual circulation type heat exchanger water pipe and a fine pipe injection flow rate is restricted less than a capability of sensing a water flow rate.
CONSTITUTION: When an additional heating mode is set with a setting unit 34, a hate exchanger 18 is heated at an ignition parr 32 so as to heat additionally the water within a bath tube 20 under a natural circulation action. At the same time, a driving valve 35 is opened and the water feeding type heat exchanger 17 starts to feed a small amount of water under a flow rate restriction part 25 and then the water is injected into the water pipe 19 at the extremity end port 39 of the fine hot water pipe 23. This injection may act upon the low temperature side, take a hot water additionally heated and mix it to each other, flow them in a bath tube without decreasing a performance of circulatiin so as to make a uniform variable temperature. With this arrangement, a safe convenient operation is assured and an efficiency can be improved.
FUJISHITA KAZUO
UEDA JIYUNICHI
