The invention relates to a heating device (1), in particular an in-line heater, for heating rod-shaped, electroconductive workpieces (13), in particular metal rods and/or non-ferrous metal rods which are conveyed along a conveying direction (R) through the heating device (1), the heating device (1) having a first heating module (2) in relation to the conveying direction (R), the first heating module (2) having a first input area (4) and a first output area (5), and a second heating module (3) in relation to the conveying direction (R), the second heating module (3) having a second input area (6) and a second output area (7).

A heat treatment system may include: a heat treatment furnace including an entrance, an exit, and an internal space in which a plurality of saggars is conveyed from the entrance to the exit; and a return line located outside the heat treatment furnace and configured to convey the plurality of saggars from the exit to the entrance. The return line may include: a first conveying device located in a first section and configured to convey the plurality of saggars; and a second conveying device located in a second section different from the first section and configured to convey the plurality of saggars by a beam or a bar.