Heating is the most important energy consumer for households in Belgium. The primary energy consumption of a heating system is determined by the net energy demand of the building, but also by the efficiency of the equipment and the way it is used by the inhabitants. To estimate the potential primary energy savings, today's situation should be analysed first. Therefore, the results of two surveys are combined to sketch current,practice in Belgium. The most common systems in Western Europe, i.e. gas boilers combined with radiators, are then simulated to test their performance in dwellings with varied insulation quality. Typical internal heat gains and set temperature profiles are included, but the influence of the inhabitant behaviour on the heating efficiency is not studied as such. The results show that current practice does lead to important energy losses, resulting in overall efficiencies as low as 30%, but improvements are possible by using intelligent controllers. However, correct boiler sizing and a sound combination of boiler and heat emitter control are still required to ensure high heating system efficiencies, especially for better insulated buildings with a high heat balance ratio. (C) 2008 Elsevier B.V. All rights reserved.