pump 32 is installed in the hot water supply circulation pipe 31 when the hot water supply circulation pump 32 is operated the stored hot water is circulated between the hot water storage tank 20 and the hot water supply device 30 for example the hot water supply device 30 is composed of a boiler type hot water supply device the hot water supply device 30 heats the hot water that inflows via the hot water supply circulation pump 32 to a set temperature for example 60 degrees c and returns the hot water to the hot water storage tank 20 again although the case in which the hot water supply device 30 is the boiler type hot water supply device is described as an example a known technique such as a heat pump type hot water supply device and a solar water heater can be applied as long as the hot water in the hot water storage tank 20 is heated here the scale of the water receiving tank 10 is generally set according to a plan one day use amount of water of a facility where the hot water supply system 1 is installed for example when a one day use amount of water per person is qd and the number of personnel who use water in a building person day is n the plan one day use amount of water is n u00b7 qd a water receiving tank capacity v of the entire water receiving tank 10 needs to be set so as not to exceed the plan one day use amount of water n u00b7 qd and is calculated by using the following expression 1 note that k is a storage coefficient in.