Abstract: A system for air-conditioning an installation having a number of rooms, the heat requirements of which are different and vary preferably with respect to time, which rooms are connected to a central air-conditioning unit. Light fixtures producing radiation heat are mounted in said rooms and are cooled in known manner by discharge air from the rooms to reduce the radiation heat. The temperature of the air from the central unit is maintained not higher than required for the room in the installation which has the greatest heat development, and the radiation heat from said light fittings is utilized and adjusted to additionally heat the rooms as described in U.S. Pat. No. 3,812,904. The adjustment provides maximum room heating by minimizing the cooling by the discharge air and minimum room heating by maximizing the cooling by the discharge air, minimum room ventilation flow being met when providing maximum heating and the flow increasing as heating is reduced.