Abstract: The invention describes an outlet system in which a characteristic of one of gas and/or a liquid, for example the percentage CO2 in air, is measured in a central outlet duct (2). The outlet system comprises local outlet ducts (5, 6, 7) that are in flow communication with the central outlet duct (2). The flow through the local outlet ducts is partly determined by corresponding flow regulators (25, 26, 27) By means of selective setting of these flow regulators by a control system (22) the local value of the characteristic can be calculated using measured values in the central outlet duct (2) and the positions of the flow regulators (25, 26, 27). By means of the invention costs of sensor controlled ventilation systems, in, for example, residential and utility building, are reduced.