In a method and with a device for preparing process gases (3) for heat treatments of metallic materials/workpieces, the respective process gas (3) is to be fed into at least one treatment chamber (1.1) in an industrial furnace (1) having been practically fully prepared, homogenised and heated, and the method is to be carried out both with newly built and particularly with already existing installations of industrial furnaces (1) with the aid of the device, wherein the process gas (3) is prepared with compression at temperatures uncoupled from the temperature in the treatment chamber (1.1), in a process separate from the heat treatment process in the treatment chamber (1.1), and in a temperature range up to about 1250° C., and is rendered usable for economical and low-emission heat treatment (FIG. 3).