The main medium flows horizontally through the gas mixer. The second medium is fed in via a laterally arranged nozzle. Swirl inserts produce a coarse mixing of the gases. Fine mixing is achieved in a downstream mixing chamber. The mixing chamber is filled with packing elements whose special shape and random arrangement of the filling material ensures good gas mixing. The packing is made of material 1.4301 and is therefore robust against abrasion and corrosion. If condensate forms, the various sections of the gas mixer should be emptied regularly. The mixed gas then flows to the outlet nozzle of the gas mixer.