This paper investigates the impact of thermal interactions between heat exchangers integrated within building foundation piles to meet space heating and cooling needs of buildings. Specifically, a three-dimensional transient numerical model is developed to evaluate the thermal performance of the foundation piles. The model is used to estimate the temperature variations within the soil medium under various operation conditions of thermo-active foundation (TAF) systems. Then, a series of parametric analyses is carried out to evaluate the influence of design parameters of the piles on the performance of TAF systems, including the interactive effects between piles as well as the impact of these piles on the building slab heat transfer. Then, the parametric analysis results are utilized to develop simplified calculation methods to assess the thermal impacts of the geometric features for the piles on both the performance of TAF systems as well as the building slab heat losses and/or gains. The developed simplified calculation methods are suitable to develop design guidelines in order to enhance the performance of thermal piles to heat and cool buildings.