The objective of this research is to grasp the effect of high insulation bathtub on heat-retention of hot water, by means of web questionnaire, laboratory experiment, and actual survey in houses. As a result, the followings were obtained; 1) It is indicated that high insulation bathtub is remarkably effective for restraining falling in temperature of hot water in bathtub, and that the insulation effect is not observed clearly when the lid of bathtub is opened even if it is the high insulation bathtub. 2) The insulation performance of bathroom also affects the decrease in water temperature as well as that of bathtub. As with insulation of the bathtub, it is important to insulate the bathroom. 3) It is suggested that to estimate water temperature drop by using bathtub heat loss coefficient would be possible.
