Due to the recent changes in social and economic circumstances, the design of energy systems has been recognized as a regional issue. In this study, we modeled the design process of a biomass energy system in the perspective of mathematical optimization problems. In a case of energy supply to basic facilities (hot bath facilities) in a hilly and mountainous area of Japan, this study evaluated the impacts of regional conditions, social system, business-based behavioral norms, etc., on the indicators such as costs, CO₂ emissions, and resource consumption through optimized selection of energy system. Results indicate that in current situations, it is possible to popularize the biomass energy system utilizing local woody biomass, while additional social burden is likely to occur.