For the pre-aeration of a steam generator a definite air stream is necessary. This is provided by a revolution-controlled fresh-air ventilator and supplied via air throttles to the individual burners. Before starting the pre-aeration, the air throttles are closed and the revolutions per minute of the fresh-air ventilator. which depend on the throttle setting, are situated in the lower range. For starting the pre-aeration, the air throttles are opened. In order to avoid a pressure drop and thus a switching off of the pre-aeration by the burner control. the revolutions per minute of the fresh-air ventilator have already to be increased before reaching the intended maximal throttle opening. The paper describes the suitable control switching for this.