Abstract <p>The article is devoted to the passage of the boiler equipment to hydrogen-containing fuel in the context of modern requirements of decarbonization of power engineering. The topicality of this investigation is due to the growing demand in hydrogen technologies and the requirements of reduction of the carbon trace in heat-and-power engineering. Potential sources of hydrogen-containing fuel (including the possibility of recycling waste gases from various systems of oil-processing plants) are considered. This study is aimed at analysis of peculiarities of heat and technical parameters in the transition to the combustion of methane–hydrogen mixtures (MHM) with different hydrogen contents using a fire-tube three-pass water-heating boiler with a power of 8 MW. In the course of investigation, a complex thermal design of a boiler has been considered for different operation modes and hydrogen contents in the fuel mixture. A special software in the Python language has been developed for the automated designing of MHM combustion processes and for heat-exchange surfaces of the boiler. The results of investigations demonstrate that an increase in the fraction of hydrogen in the fuel to 20% makes it possible to increase the boiler efficiency by 0.1%, while the complete transition to hydrogen increases the efficiency from 0.4 to 1.3% depending of the load of a boiler aggregate. In this case, a substantial decrease in the discharge of CO₂ to the atmosphere is observed, while after the complete transition to hydrogen, carbon dioxide outbursts are absent. However, a transition to hydrogen fuel requires analysis of a number of technical limitations (reduction of the caloric power, increase of volume flow rate of the fuel, and changes in combustion type and heat transfer). The practical importance of this study is the assessment of operation parameters of the actual energy equipment of a power system. Our investigations have revealed the effectiveness of a gradual increase of the hydrogen fraction in the fuel mixture as a compromising decision between environmental requirements and technical and economic indices.</p>