The article deals with the implementation of the new national environmental legislation, which provides for the division of all energy enterprises into 4 categories depending on the degree of negative impact on the environment, the introduction of technological rationing, implemented on the principles of the best available technologies, provided that they are technically possible to use them, and the differentiation of state regulation measures in the field of environmental protection. Within the framework of this approach, the values of the total index of harmfulness (toxicity) of combustion products formed during the burning of Berezovsky coal of the B2 grade (enrichment class P) were determined by numerical experiments in order to assess the impact on the environment of emissions from low-power boilers KE-25-14C. The total emission hazard index is determined by taking into account the contribution of specific hazard indicators of combustion components represented by nitrogen oxides, sulfur dioxide, carbon monoxide, ash particles, vanadium pentaoxide and benz(a)pyrene. The private contribution of the considered pollutants to the total toxicity of emissions in the implementation of combustion regimes with moderate and large chemical underburning of fuel is established. Practical recommendations are given for using the results of the study as input data for setting technological standards for boilers of thermal power plants in the process of approval and obtaining a comprehensive environmental permit, and for developing a program to improve the environmental efficiency of energy enterprises.