The European Union has declared the goal of achieving climate neutrality by 2050, ensuring economy with zero net greenhouse gas (GHG) emissions. To achieve this goal, the EU has announced European Green Deal, which includes an action plan to accelerate efficient resource usage while moving towards circular economy, as well as to restore biodiversity and reduce pollution. The transition to climate neutrality is urgent and offers an opportunity to build a better future. In order to achieve climate neutrality, society and all economic sectors must play their part. Increasing the efficiency of heat production and reducing consumption is considered one of the key tools for achieving the EU's climate and energy goals by 2030, which envisage at least a 40% reduction in GHG emissions, using 1990 as a baseline, at least a 32% share of renewable energy and a 32.5% increase in energy efficiency. In accordance with the EU climate and energy policy, the Latvia’s National Energy and Climate Plan 2021–2030 has been developed, and it includes national objectives and main actions that are directly or indirectly related to the increase of the efficiency in heat energy production and the reduction of consumption focusing on renewable energy. The overall aim of the present Doctoral Thesis is to evaluate heating systems in Latvia using sustainability indicators, including heat energy producers and end-users. Make proposals on potential methodologies to increase the efficiency of the heating system and to reduce GHG emissions, emphasizing the use of renewable energy sources. An evaluation of various technologies and methods has been developed, which offers complex solutions for increasing the energy efficiency of heat energy producers. The Thesis is designed as a set of publications, which combines parts of scientific publications written during doctoral studies. Publications are presented in several scientific conferences. The introduction describes the aims and tasks of the work, as well as the scientific and practical significance of the work. The first chapter examines the scientific literature, which includes a review of the indicators and methods used in the heating sector, as well as a review of the Latvian heating system. The second chapter describes the methodologies for sustainability indicators for heating sector used in the Thesis. The third chapter describes the results obtained in the Thesis and its analysis. Finally, conclusions and recommendations for obtaining and using sustainability indicators for heating system are provided. The Thesis is based on 9 publications and approbated in six scientific conferences.