Abstract: An apparatus for temperature control in a room by adjusting supply air flow rate in response to a room thermostat in a ducted air conditioning system where a plurality of rooms are supplied by a single air handling unit. The apparatus may be installed in a plenum which is directly mounted on an air supply terminal. The apparatus is connected to a main supply duct with a branch duct, and as a result of its favorable geometry and throttling method, operates at low noise levels. The apparatus employs high aspect ratio converging nozzles to allow incoming air accelerate into a thin sheet of high velocity air stream. Air flow rate is adjusted simply by changing tile nozzle area. This high velocity air stream entrains surrounding air within the plenum and slows down. Its energy is dissipated through friction with acoustically lined plenum walls. In tiffs process, little noise generated. The apparatus, due to its special shape, allows accurate measurement of air flow rate.