This investigation concerns thermal stratification of the water due to the temperature difference (${Delta}T=T_{infty}-T_i$) between the mean temperature of the water in the test tank (1m wide, 1m high, 2.1m long) and the temperature of the inflow water into the tank; flow rate of circulating water and height of the sink diffuser in the test tank. The additional objectives was to observe a stratification phenomena near an interface by measuring the velosities and the temperature difference and investigate an availabilities of the better effective hot water through establishing thermocline near an interface around the bottom of the tank. Following results were obtained through the experiments. 1. When the flow rate was constant and the temperature difference (${Delta}T=T_{infty}-T_i$) between the mean temperature of the flow in the test tank and the temperature of the inflow water increased by 5.6, 9.5, 13.5($^{circ}C$), obtained the better effective advantage of hot water and the stress near an interface increased gradually. 2. When the ${Delta}T=T_{infty}-T_i$ was constant and flow rate increased by 4.0, 4.8, 6.4, 8.0 (LPM), obtained the better effective advent age of hot water and the mean stress near an interface increased gradually. 3. When the height of the sink diffuser was 25cm from tank bottom in comparison with 50cm, obtained the better effective advantage of hot water and the mean stress near an interface increased.