The aim of the work is to simulate and analyze the efficiency of combustion of methane-hydrogen mixture in an environment with increased oxygen content, and in the limit - in pure oxygen, in a fire-tube boiler to reduce CO2 emissions. To achieve this goal, the following problems were solved: development of a mathematical model of a three-pass fire-tube boiler for operation when burning a natural gas and a methane-hydrogen mixture in air and a mixture of air with pure oxygen, a numeri-cal study of the boiler operation when burning a methane-hydrogen mixture with a hydrogen con-centration from 0 to 40% and replacing air with oxygen from 0 to 100%, assessing the efficiency of equipment in these modes. The most important result is the confirmation of an increase in the effi-ciency of the fire-tube boiler when switching to combustion of methane-hydrogen mixture in an environment with increased oxygen content. The significance of the obtained results lies in determining the most effective parameters of equipment operation, contributing to an increase in the efficiency and environmental friendliness of the heat generation process. The study was conducted for two modes: combustion of a methane-hydrogen mixture with a hydrogen concentration of 0 to 40% in air and combustion of a methane-hydrogen mixture with a fixed hydrogen concentration in air with an oxygen concentration in the range from 0 to 100%.