An electrical thermal storage (ETS) device for space heating is designed in this study. The proposed device is charged by the off-peak electricity and releases its thermal energy to warm the space all day long. The natural convection occurring in the flow channel drives the flowing of air to be heated up and warm the space. The dynamic process of a fully charging/discharging cycle of the device is tested. Meanwhile, a three-dimensional model is developed to simulate the transient thermal behavior. It is found that the experimental and numerical results agree with each other which indicates the validation of the proposed numerical model. The results show that the temperatures of the bricks and the outlet air can be as high as 1002 K and 835 K, respectively. The natural convection occurring in the flow channel transfers 40.4% of the total electrical heating energy to the space for the charging process and 26.9% for the discharging process. Heat losses to the space through the adiabatic material shares 13.3% of the total heating energy for the charging process and 7.2% for the discharging process. Based on those findings, three methods are recommended to improve the device in the successive research.