The aim of the research paper is to create a model that can calculate exergy balance of a district heating system (DHS) and to analyse the resulting model based on Ludza DHS. A calculation model of exergy of a DHS is proposed, which is based on a thorough mathematical calculation algorithm of heat and mass exchange processes, which includes the necessary information about the each block. The approbation of the exergy balance model on the base of Ludza city heat supply system shows the following: the average exergy factor during calculation period is 0,17; the average losses of exergy due to the losses of heat during the calculation period is 8,54%; the average exergy losses during transportation of heat carrier is 13,26%; the average exergy losses in heat exchanger is 10,92%