This paper presents a heat transfer model for thermally active drilled-shaft foundations used for heating and cooling buildings. Specifically, this paper presents a numerical approach to evaluate the unsteady temperature distribution within the ground medium surrounding the foundation as well as indoor/outdoor heat fluxes. In particular, a 2-D numerical solution was obtained using the finite difference technique with a purely implicit solution scheme. The results of the sensitivity analysis indicate that the efficiency of the thermo-active foundation can be significantly improved with a proper selection of design parameters including flow velocity, foundation depth, and foundation materials.