The aim of this study was to identify changes in the Polish heating sector and assess modernization investments in the field of energy transformation. This research covered 30 municipalities in Poland that applied for the II National Competition for Local Government Units for the Most Energy Innovative Local Government. In terms of changes, the analysis covered the years 2002–2021 and in the investment assessment, data from 2021 were used, as well as plans and strategies of enterprises and local governments. To assess planned investments in district heating companies, an original method of assessing social needs and the ability and readiness of enterprises to modernize the infrastructure in the field of heating was developed. It considers the emissivity factor of a heating plant and the assessment of investments by experts according to nine criteria. The method was used to assess changes in the district heating system in 30 municipalities in Poland. The shaping of the energy strategy in Poland is influenced by the climate and energy policy of the European Union (EU), which assumes that by 2040, households and industries will be heated with system heat or low-emission energy sources. Poland is the second-largest district heating market in the European Union, but heat production in the country is dependent on coal, which is why this sector requires transformation in the coming years. Research shows that thermal energy companies modernizing their installations more often use low-emission technologies than zero-emission ones. The main objectives of investments in energy production are the decarbonization of the heating system and a reduction in greenhouse gas emissions, as well as social needs in the field of connecting houses and flats to the system networks.