The article discusses the importance of determining and monitoring the composition of flue gas from burning solid fuels for efficient combustion, safety, and environmental protection. A web application was developed to help engineers and researchers calculate the amount of air needed for combustion based on fuel composition, excess air, and flow rate. This tool can be used during equipment design and operation to optimize combustion efficiency and reduce pollution. Proper control of the combustion process leads to better equipment performance, cleaner emissions, and lower thermal losses.