In this thesis, a thermodynamic calculation of a steam generator fired with solid and gaseous fuel has been performed. The division and parts of the steam generator and the losses in the steam generator itself are described. The application of steam generators is wide. It is used in the food industry, oil industry, ship propulsion, etc. A mathematical model was written for the calculation of steam generators using solid and gaseous fuel. A steam generator was used that produces fifty tons of steam per hour. The main data when designing a steam generator are the temperature and the evaporation pressure. The main goal of this paper is to use fuel whose combustion will produce the least amount of harmful smoke gases. After the mathematical model was written, the obtained results for solid and gaseous fuel were presented. The transfer of heat on the heating surfaces, the exit temperature of the flue gases, and the dimensions of the firebox and heating surfaces were analyzed. An analysis of the impact of greenhouse gas emissions on the environment was also made. The calculation resulted in the result that a gas fuel steam generator produces less carbon monoxide and produces more water vapor compared to a solid fuel steam generator. The degree of utilization of the steam generator and fuel consumption are affected by the losses. Solid fuel steam generators contribute to a greater increase in greenhouse gases than gaseous fuel. Seen from an ecological point of view, steam generators fired with solid fuel (coal) represent the most dangerous type of fuel, since its combustion produces more harmful gases. In order to reduce emissions of harmful gases in the atmosphere, various agreements were signed, such as the Kyoto Protocol and the Paris Agreement. Today, states and various competent institutions implement measures to reduce emissions of harmful gases.