Also, the water-temperature-sensing ratio control (Case 3) has the same characteristics as those of the changes in indoor mean temperature shown in Fig. 13. The air-sensing On – Off control (Case 4) has an unstable total supply heat amount. This is because the time-point in the On – Off is subject to change with the temperature of hot-water supply, creating a change in the final indoor temperature, even though the mean temperature is similar as shown in Fig. 13.