Abstract Thermal energy storage tanks are highly insulated in order to minimize the heat losses through the top and lateral walls and the foundation. Typical tanks of state-of-the-art solar power plants include a ventilation system within the foundation in order to ensure that the working temperature reached in the concrete remains below a maximum allowable value. In the present work, a multilayer analytical model for the estimation of the tank’s bottom heat losses in steady state is developed, including separately the quantification of the heat losses due to the ventilation system and the heat loss to the soil. A new correlation for the soil equivalent thermal resistance (which is unknown a priori) is previously obtained using a numerical model which is validated with the results of other authors. A comprehensive parametric analysis of the variables of interest is made and a set of cases covering a wide range of tank geometries, insulation levels, storage temperatures and maximum allowed concrete temperatures are solved. Finally, the obtained results are summarized, providing a quick method for the estimation of the total bottom heat losses and its components (the ventilation heat losses and the heat loss to the soil). These results provide useful information related to the tank foundation design, such as the quantification of the evacuated heat due to the ventilation system or the selection of an appropriate bottom insulation thickness level depending on the tank geometry, the storage temperature, the ventilation system and the type of soil.