The book covers the main issues of the general theory of heat operation of furnaces, as well as the technology and principles for calculating the processes of melting steel, heating ingots and blanks and drying materials. Design and operation of smelting, heating and drying furnaces used in black and non-ferrous metallurgy and mechanical engineering are considered. Elements of structures and auxiliary equipment of furnaces are described: devices for heat generation (burners, nozzles, electric heaters), for utilization of heat of leaving gases, for obtaining compressed air, steam and oxygen gas purification devices.