Treatment system for treating workpieces, comprising: - a treatment chamber, which comprises a plurality of treatment chamber portions, each of which is assigned to one of a plurality of separate circulating-air modules of the treatment system, each circulating-air module being arranged to guide a separate, circular gas flow; - a heating system, which comprises a self-contained heating-gas guide in which at least some of a heating-gas flow can be guided in a circuit, a plurality of circulating-air modules being coupled to the heating-gas guide, in particular for heating the gas guided through the treatment-chamber portions, characterized in that the heating-gas guide comprises one or more bypass lines for bypassing all the circulating-air modules and/or treatment-chamber portions, the heating-gas guide comprising a circulating-air guide which is formed in portions by a plurality of circulating-air modules arranged in parallel, a) a bypass line being arranged downstream of a plurality of branches and/or junctions of the heating-gas guide for supplying heating gas to the circulating-air modules and/or b) a bypass line being arranged upstream of a plurality of combining means of the heating-gas guide for combining gas flows from the circulating-air modules. - a treatment chamber, which comprises a plurality of treatment chamber portions, each of which is assigned to one of a plurality of separate circulating-air modules of the treatment system, each circulating-air module being arranged to guide a separate, circular gas flow; - a heating system, which comprises a self-contained heating-gas guide in which at least some of a heating-gas flow can be guided in a circuit, a plurality of circulating-air modules being coupled to the heating-gas guide, in particular for heating the gas guided through the treatment-chamber portions, characterized in that the heating-gas guide comprises one or more bypass lines for bypassing all the circulating-air modules and/or treatment-chamber portions, the heating-gas guide comprising a circulating-air guide which is formed in portions by a plurality of circulating-air modules arranged in parallel, a) a bypass line being arranged downstream of a plurality of branches and/or junctions of the heating-gas guide for supplying heating gas to the circulating-air modules and/or b) a bypass line being arranged upstream of a plurality of combining means of the heating-gas guide for combining gas flows from the circulating-air modules. a plurality of circulating-air modules being coupled to the heating-gas guide, in particular for heating the gas guided through the treatment-chamber portions, characterized in that the heating-gas guide comprises one or more bypass lines for bypassing all the circulating-air modules and/or treatment-chamber portions, the heating-gas guide comprising a circulating-air guide which is formed in portions by a plurality of circulating-air modules arranged in parallel, a) a bypass line being arranged downstream of a plurality of branches and/or junctions of the heating-gas guide for supplying heating gas to the circulating-air modules and/or b) a bypass line being arranged upstream of a plurality of combining means of the heating-gas guide for combining gas flows from the circulating-air modules. a) a bypass line being arranged downstream of a plurality of branches and/or junctions of the heating-gas guide for supplying heating gas to the circulating-air modules and/or b) a bypass line being arranged upstream of a plurality of combining means of the heating-gas guide for combining gas flows from the circulating-air modules.