Condenser in horizontal design with exchangeable U-tube bundle. The condensing steam is led through the shell. The bundle tubes are attached by expanding or shrink-welding or both (depending on the operating conditions). Condensate supercooling is possible but then a fill level limitation must be installed. The heat exchanger is controlled by a steam control valve. The condensate must not accumulate beyond the maximum volume, not even due to operating conditions such as downtimes, zero load or tube routing. If applicable, inert gases can be easily discharged. Nozzles for the discharge of inert gases are available if required. There is no strong barrier layer formation as in narrow channels (e.g. plate heat exchangers).