Electric load levelling is one of the urgent requirements for the utility power industries in Japan. As a solution to this requirement, the intensive heat storage system utilizing surplus power during off-peak hours at nighttime was chosen for heating rooms and water supply in buildings, such as hotels and hospitals. This paper describes the conceptual study of a sensible heat storage system with solid storage material and its thermal characteristics. The system was assumed to be composed of a storage core of refractory bricks, an electric heater, a steam generator, and a fan for the recirculation of air to transport heat among these components. It was found through analysis that the lower air velocity, the narrower air passage in the core, and the thinner brick resulted in the increase of the amount of heat storage for a given volume of the core.