PURPOSE: To shorten the time of flow of cold water immediately after starting to use the hot- water supplying device and permit to supply sufficient amount of hot-water after hot-water temperature has become normal by a method wherein a double tube is provided in the hot- water pipeline of the gas hot-water supplying device and the flow amount of hot-water, flowing through inner and outer tubes, is regulated in accordance with the temperature of hot- water.

CONSTITUTION: The inner pipe 9 is provided in the hot-water pipeline of the hot-water supplying device and valves 10a, 10b are attached to a clearance between inner and outer pipes 9, 6. The valves 10a, 10b are made of shape memory alloy and when the temperature of hot-water is lower than a given temperature, the valve 10a becomes conical to shut the clearance between pipes 9, 6 and flow hot-water only through the inner pipe 6, however, when the temperature of hot-water is higher than the given temperature, a gap is generated between coils of the vlave 10b and hot-water flows through the inner and outer pipes 9, 6. Immediately after starting hot-water supply, the valve 10a is in a condition shown by the diagram and the volume of low-temperature water in the inner pipe 9 is small, therefore, the water can be discharged in a short period of time, thereafter, when hot-water, heated in the heat exchanger of the hot-water supplier, comes there and the temperature becomes higher than the given temperature, the gap is generated between coils as shown by the valve 10b in the diagram, then, hot-water flows through inner and outer pipes 9, 6 and the flow amount is increased to a proper value. Accordingly, the period of time wherein low-temperature water is discharged may be shortened while the flow amount to meet the demand of the hot-water supplying device may be flowed after the hot-water temperature has arrived at the temperature of practical use.