In recent years, the use of the air-based solar heating systems, which heat outdoor air and use it for heating and hot water, has increased in Japan. Air-based solar heating systems do not require special equipment for heating by direct use of air heated via convective heating, and they can be used for the hot water supply through heat exchange when the room temperature is high. However, because solar energy is only available during the daytime, and because of heat loss to the ground from the foundation concrete (which is a thermal storage body storing the collected heat), the load reduction effect is much less than the amount of the heat that is collected by solar heating. In this study, a simulation model was developed to understand the annual thermal load performance of an air-based solar heating system. The models of the solar collector, hot water tank and thermal storage were verified by comparison with experimental results. In order to improve the thermal performance of conventional systems, the solar collector, indoor air circulation, insulation under the foundation concrete, and additional thermal storage were examined. In particular, this study examined the effect of solar heat using water bottles that can achieve a large thermal storage effect at low cost. Simulation results show that the proposed system reduces annual heating and hot water load by 17.9% compared to conventional systems.