This paper compares district heating systems in Zagreb and Aalborg in order to see their similarities and differences from which conclusions are drawn on how to improve the systems. The method chosen is the comparative analysis. Data is organized and structured so to allow clear and concise comparison. The results of the comparative analysis show that the district heating system in Aalborg is more advanced than the district heating system in Zagreb. This advantage is prominent in aspects of supply, demand, distribution and economic spheres. Some of the possible improvements include lowering specific heat and water losses. Systematic replacements and refurbishments of the old network pipes are key to this. Lowering the supply and return temperatures would enable better renewable energy sources integration. The integration of renewable energy sources in district heating systems is the most important goal that still needs to be achieved. (C) 2015 Elsevier Ltd. All rights reserved.