A procedure for calculating heat transfer in steam boiler fireboxes is developed proceeding from the scientific discovery of laws pertinent to radiation from torch gas layers. By using this procedure, it is possible to determine the distribution of heat flux densities both along the height and perimeter of all waterwall surfaces in a firebox and to calculate the maximal densities of incident heat fluxes. Examples of heat transfer calculation in a torch furnace and steam boiler firebox carried out using the procedure developed on the basis of the above-mentioned discovery are given. The calculation results are in satisfactory agreement with the results of heat transfer measurements in a torch furnace and steam boiler firebox. The difference between the calculated data and measurement results does not exceed 12%.