A comprehensive methodology has been developed to assess the efficiency potential of national heating networks. Considering the available information on heating networks in Latvia, three different heating system models have been identified depending on the district heating (DH) system scale. To determine the total length of heating networks in populated areas, a regression analysis method is used by analysing the correlation between the inhabitants and the length of heating networks. Authors define different alternatives for heat loss reduction, including the renovation of existing heat pipes and lowering heat carrier temperature. An engineering model is prepared for each alternative based on mathematical calculations to evaluate the economic, environmental, and climate impacts. Estimated costs and savings are used to determine the key economic indicator — net present value (NPV). The results show that the potential reduction in national heat losses from heating network renovation is estimated at 569 GWh. It would reduce the national heat loss rate from around 12% to 6% from the produced heat. Lowering the heating network temperature saves an additional 57 GWh. However, the main benefit of lowering heat carrier temperature is the possibility to use low-cost plastic pipes, which increases the overall economic benefit of the heating network renovation.