The European Union has set a goal of reducing greenhouse gas (GHG) emissions by 20% by 2020, compared with 1990 levels, and increasing the proportion of renewable energies in the energy mix to 20%. It is also discussing a possible 30% decrease in GHG emissions. The main fields for the reduction of GHG are raising the energy efficiency of energy systems and the replacement of fossil fuels with renewable energy resources, including biomass. Even though the possibilities of biomass as an alternative fuel are well known, analyses of the cost and economic benefit of fuel replacement and biomass use are still necessary and are currently being done. The use of bio-energy to produce energy is an attractive solution due to its high potential and diversity of use; it can be used for the output of heat, cogeneration and bio-fuel production. The goal of the dissertation is to develop and approbate methods for evaluating existing and new technological solutions of district heating systems from the perspective of energy efficiency, cost and environmental protection. To achieve this goal, an analysis of the possibilities and results of integrating a flue gas condenser and heat pump into a district heating system has been performed; an evaluation diagram for the operation of a boiler house with condenser has been developed; an energy management system at a system’s energy source has been created that determines energy efficiency characterising indicators, benchmarks and changes in indices; an economic evaluation of the use of a flue gas condenser at a system’s energy source has been performed; and, based on an analysis of operational data, an economic evaluation of the use of a flue gas condenser at a system's energy source has been performed as well as an evaluation of a district heating system’s influence on the environment, using the eco-intensity indicator. The dissertation is based on five [1; 2; 3; 4; 5] main publications. Other studies of district heating system operations published by the author are examined in the overview of these works, the goal of which is to inform readers about issues that have not been included in this dissertation. The dissertation consists of four sections: an introduction, an overview of the literature, study methodologies, study results and analyses thereof. In the first section, the study goals and tasks are defined, the structure of the dissertation is explained, and a short description of the author’s studies is given that covers both the main publications and other studies by the author regarding the analysis of district heating systems. The second section provides an overview of the literature and focuses on the necessary studies regarding aspects of district heating system operations and the improvement thereof. The third section examines the research methodologies of the issues studied in the main publications. The results obtained in the study and the analysis thereof are presented in the fourth section. Conclusions are presented at the end of the dissertation.