The decarbonization process and the transition to sustainable sources, driven both by climate needs and geopolitical reasons, require existing and new-designed DH systems to effectively integrate in this picture. Among the characteristics required by the so-called 4th generation systems, the capability of working with low supply temperature is crucial for the introduction of non-fossil energy sources. While low temperature represents a great potential, the adaptation of existing systems to this new working condition introduces some challenges. On the road to the reduction of supply temperature, numerical analysis is crucial for the prediction of the response of the system to changes in operating conditions.