Disclosed is an air-conditioning apparatus for use in controlling the temperature of air in and delivered to a plurality of rooms or spaces. The apparatus has a central utility means which supplies a pressurized volume of cold air. Ducting is provided to connect the cold air supply to a plurality of distribution units, at least one of which is mounted in the vicinity of each room or space. Each distribution unit has a mixing chamber which is in fluid communication with the ducting to allow cool air to flow from the ducting into the mixing chamber. Mounted within the mixing chamber is a blower which causes air to flow from the interior of the mixing chamber through an outlet into the room to be conditioned. Control means are present in the ducting adjacent the distribution unit to sense the presence of pressurized cool air and in turn actuate the unit and blower to cause a flow of air from the mixing chamber. An inlet damper is provided to control the flow of cool air from the ducting into the mixing chamber. A temperature sensing means is located in the room to control the inlet damper and in turn regulate the flow of cool air into the mixing chamber in response to the temperature of air in the room. A second control means is connected to the inlet damper to control the pressure of the air within the mixing chamber. A second inlet is provided to allow air to flow from the room into the mixing chamber. A barometric damper is provided to control the flow of air through the second inlet in response to the pressure of the air within the mixing chamber. A selectively operable heating element is provided in the outlet to heat the air moved by the blower from the mixing chamber into the room. Control means are connected to the temperature sensing means to operate the heating element in response to the temperature of the air within the room.