Installation of residential solid-oxide fuel cell cogeneration system (SOFC-CGS) has been promoted as an energy-saving measure. Although SOFC-CGS is becoming popular among detached housing, the installation of SOFC-CGS in apartment buildings can also be effective in reducing residential energy consumption. In this study, the effectiveness of SOFC-CGS installation in an apartment building is evaluated by considering the variation of eletricity and hot water demands in different household settings. In order to simulate the demands, parameters are formulated and randomly distributed in a 50-unit apartment building model. The reduction rate of energy consumption by SOFC-CGS installation is generated for each unit and the impact of each parameter is examined.