Abstract: The invention relates to a process for starting up a heat exchanger system for the generation of steam accommodated in a hot gas line, in particular in an exhaust gas line, conveniently in a waste heat boiler, for instance downstream from a gas turbine, for instance for starting up a circulation system steam generator or a continuous flow (once-through) steam generator, conveniently a natural or forced circulation boiler or once-through boiler, in particular a preheater/evaporator/superheater system provided with a start-up heat exchanger upstream via which the supply of feed medium, in particular water or steam, is effected, and which on start-up dispenses first hot steam and finally water to the heat exchanger system, so that the initially pressureless, void heat exchanger system substantially heated to hot gas temperature is continuously brought to its operative state and its operating temperature, as well as a corresponding heat exchanger system.