This work aims at developing a potential analysis of the diffusion of renewable-based low temperature district heating systems, through the mapping of energy demand, renewable and waste heat sources using the Italian city of Milano as a demonstrative case study. This analysis starts from the question to seek what would be the future sustainability of district heating in the framework of the foreseen scenario of building refurbishment and consequent reduction of heat demand. District heating has proven to be a recognised way to efficiently distribute renewable energy in dense urban areas. But the feasibility of this energy system is questioned in case of low heat demand and scarce availability of waste heat sources. Milano is a densely populated city, with an intense energy demand, where district heating has a low market share (<10%), which leaves the important issue of sever air pollution and where there seems to be no availability of renewable energy source. This work has been developed together with the local DH utility in order to support the municipality in defining the priority measures to be implemented in the next years in the local Environmental Plan. The developed analysis shows that DH has a wide undeveloped potential in the city which could benefit of an important amount of renewables and waste heat recovery if the temperatures where decreased by benefitting in reality by a massive energy refurbishment. The results show that the development of renewable-based low temperature district heating is not an alternative nor in competition with building energy refurbishment, but complementary. The feasibility is based on a mapping of the available waste heat sources in the city namely, industrial sites, waste water treatment plants, metro stations, datacentres, and ground water wells. For a total residential demand of 8 TWh, results showed that 6 TWh could be technically potentially covered by DH, out of which 80% at same or lower distribution costs than the existing DH system in the city. Considering the future energy demand, an energy reduction scenario has been considered in accordance with the national energy strategy for 2050, which foresee the 60% of the building stock going through important energy refurbishment. The estimated energy needs for this fraction of refurbished building stock amounts to 5 TWh out of which 2 TWh can be fed by low temperature plastic network at the same distribution costs of current 3GDH. In parallel to this reduction of energy needs, the reduction of temperature characterizing 4GDH systems opens the door to a wider set of low temperature heat recovery: the outcomes of the mapping and quantification of low temperature heat sources shows a potential of 4.5 TWh of recoverable heat in the city which increases to 5.2 considering also the surrounding suburbs. The outcomes of this works confirm the results of Stratego projects which identified the nut region surrounding Milano has a heat synergy regions and it emphasize this results by showing the effect of widening the range of heat sources by lowering the demand of network.