The main design features and elements of industrial shaft furnaces are described. It is indicated that one of the undesirable phenomena in a shaft furnace is a large temperature gradient along its height; in this regard, the processes of air mass transfer through various parts of the furnaces are considered. The relationships and limitations that determine such a negative effect as the possibility of external air diffusing into the furnace through its walls are formulated. The results can be used to increase the quality of shaft furnace designs and the applied heat treatment processes.

Keywords: electric furnaces, heat treatment, tightness, gas permeability