Japan needs to improve its residential energy efficiency to reduce energy consumption and thus achieve its greenhouse gas (GHG) emissions reduction targets. Understanding the differences in household behavior and energy use is important to evaluate the effect of energy conservation measures. In this study, the authors propose a new method for household energy use modeling based on questionnaire surveys on home appliances and hot water use. Fifteen-minute residential electricity and heat demand profiles with different seasons, household structures and lifestyles are obtained from the survey results, and compared with available statistical data. The replacement effects of refrigerators, TVs and lighting on residential electricity savings, net present value (NPV) and GHG reductions are evaluated using calculated energy demand. Variations in household energy use are considered under different change scenarios in household structure and by conducting an uncertainty analysis based on the Monte Carlo method. The results indicate that GHG emissions can be reduced by purchasing a new refrigerator, and electricity costs can be reduced by installing LED lamps in the living/dining room. It is also found that there is a wide range of uncertainty for NPV and GHG reductions after replacing a TV because different households watch TV for different lengths of time.