The results of experimental studies of the thermal decomposition processes of composite fuels based on long-flame coal (the Listvyazhnoe deposit) and based on timber industry wastes (Dzerzhinsky LPK, Tomsk) are presented. The main characteristics of composite fuels are determined: heat of combustion; humidity; ash content; release of volatiles; influence of thermal decomposition degree on temperature; the scale of the decrease in the emissions of anthropogenic gases with an increase of wood concentration in composite fuel is established. An effective composite fuel composition has been established as 50 %/50 %. At this concentration, energy characteristics decrease by less than 9 %, but yield of fly ash and SOx, NOx oxides is reduced by 34 % and 30 %, respectively. The conducted experimental research allows justifying the possibility of using these composite fuels for combustion in steam and hot-water boilers.