The development of a district heating systems calculation model means improvement in the energy efficiency of a district heating system, which makes it possible to reduce the heat losses, thus positively affecting the tariffs on thermal energy. In the paper, a universal approach is considered based on which the optimal flow and temperature conditions in a district heating system network could be calculated. The optimality is determined by the least operational costs. The developed calculation model has been tested on the Ludza district heating system based on the technical parameters of this system.