The invention relates to fire-fighting installation comprising a drive source for feeding medium into at least one heat releasing spray head (4), the drive source comprising a pump unit (5) for feeding liquid into said spray head through a supply line (3) which is filled with gas to a standby pressure, a gas source (9) for maintaining the standby pressure, and a sensor (2) arranged to provide a signal for starting the pump unit in response to a change occurring in the state of the medium in the supply line. In order to rapidly start the pump unit (5) of the drive source as a result of a minor flow occurring in the supply line (3) and in order for the fire-fighting installation to be applicable to be used at low temperatures, the sensor is a flow transducer (2) arranged to provide a signal to the pump unit (5), if the flow of gas in said portion of the supply line exceeds a certain predetermined value.