The accurate dynamic determination of the average energy demand of an underground space is difficult because the soil surrounding the rooms is a semi-infinite space and its temperature varies in annual cycles. In this paper a method is presented for dimensioning underground spaces in terms of heat transfer characteristics and thermal comfort. The dynamic physical and mathematical model with initial and boundary conditions have been developed. Within the procedure of mathematical modelling the heat transfer properties, the heat comfort model and the simulation algorithm of underground spaces have been created. The obtained simulation results are presented in diagrams in favour of the quick sizing of the required heating and cooling performance of underground spaces. The presented diagrams can be used in an effective manner also for the calculation of thermal comfort in underground spaces. These are new in our paper. (C) 2015 Elsevier Ltd. All rights reserved.