Optimizing energy systems is, in Sweden, as in many other countries, of growing interest. District heating systems are no exception. In 2012, 285 out of 290 municipals in Sweden had district heating in use and the majority of these systems have a higher return temperature than that which is possible with an error-free substation of day current technology. To, when possible, lower the return temperature is a way of increasing the effectiveness of the district heating system.This study means to investigate, through simulations and calculations, how big of a reduction in production cost a lower temperature in the city of Ystad’s district heating system would correspond to. The results show that a cold year, such as 2010, 1.8 SEK of the production cost could be saved per MWh sold heat for a whole year and 1°C temperature lowering. Equivalent value for a warm year such as 2011 was concluded to be 1.2 SEK/MWh,°C.