PURPOSE: To preheat a material to be melted economically by utilizing effectively the sensible heat of high-temperature waste gas by a method in which high-temperature waste gas from the waste gas path of an electric oven is partially brought into contact with a material to be melted for charging into the electric oven to heat it by means of a convectional heat transmission.

CONSTITUTION: High-temperature waste gas discharged from the electric oven 1 is introduced into the upper part of the primary cooler 3 and then the waste gas from the cooler 3 is directed to the lower part of the secondary cooler 5, where it is cooled by atomized cooling water and then discharged through the dust collector and then the stack 8 by means of the inductive air blower 7. Part of the waste gas at the outlet of the cooler 3 is directed through the damper 9a into the dust collector 10 and then introduced into any of the paired preheaters 14 and 15 through the blower 12. In the oven 14, for example, the comparatively high-temperature waste gas comes into contact with scraps to heat the scraps by convectional heat transmission. The waste gas cooled by the heat exchange is returned to the upper part of the primary cooler 3.