Steam generator in horizontal design with exchangeable U-tube bundle. Steam, hot water or thermal oil are employed as heating media. This type is suitable for low to medium shellside steam pressures. The bundle tubes are attached by expanding or shrink-welding or both (depending on the operating conditions). The flow can be double- or multi-flow depending on the fluid throughput. If condensing steam is employed as heating medium, the heating tubes are installed at an angle in order to ensure that the condensate is properly drained. The condensate can be cooled down by an external heat exchanger. With a low steam space load good buffer conditions can be achieved if the steam is used irregularly. As stainless steel version the RDE 2002 type is suitable for pure steam generation.