The course is focused on the basic characteristic and allocation the secondary energy sources. Describing the energy looses, energy potentials and also the fuel saving. The secondary energy source is defined through the secondary fuel, secondary enthalpy/heat/chill and secondary pressure. Exhaust-heat boilers, turbine, microturbine and heat pumps are described. The low-potential heat and utilization of energy from metals, coke and slags are described too.