Energy efficiency is one of the most pressing topics now. Energy consumption in-creases as living standards rise. Efficient heat production, i.e. efficient use of energy, is achieved with optimal boiler load. The second pressing issue is the protection of the environment from pollution. The process of burning different types of fuels to produce heat or energy results in emissions that can have negative impacts on the environment. One of the solutions to improve air quality is to reduce emissions from heating plants during their production. The scientific paper considers the possibility of a preheating and humidification for combustion air system to increase the efficiency of the boiler and reduce the amount of harmful emissions in flue gases. The boiler efficiency values were calculated before and after the installation of the preheating and humidification system for the combustion air, and measurements of the flue gas analysis were carried out using a Testo 350 flue gas analyzer. Calculations and measurements for flue gas analysis have shown that the combustion air preheating and humidification system increases the boiler house efficiency by 15 % and re-duces nitrogen oxide emissions by 70 %.