Abstract: A hotel floor comprises rooms each provided with a central heating radiator having a valve adjustable by means of a 0-10V dc stepper motor. In the hotel lobby a sensor for ambient temperature is connected to a radio transmitter and radio receivers are connected to the stepper motors in each room. If the ambient temperature falls, the transmitter transmits to the receivers a signal representing the lower temperature, and the stepper motors open the valves. If the temperature rises, the transmitter transmits another signal, and the stepper motors close the valves. Thus, the heat output of the radiators is varied in inverse relation to the ambient temperature. The system may otherwise control lighting fittings by way of dimming ballasts, and may also include person-detectors, timers and further control components.