Abstract: An HVAC control system is described comprising: a server (32) having planned information, a man-machine interface (50) capable of communication with the server (32) to provide dynamic information about building occupancy based on a change in cold water in a mains riser. A central control unit (28) which can communicate with the server (32), and a room node (22, 24) for providing information about conditions within the room whereby, the information about room conditions is compared to planned information and/or dynamic information and adjustments made accordingly. The room node (22, 24) may comprise sensors (276, 278, 272, 274) which provide information about conditions in the room. Dynamic information can include changes to planned occupancy, the effect of solar heating and weather conditions. Changes to planned occupancy can be established through detecting location (internally or externally) or destination of a user; and calculating estimated time of arrival of a user.