Two dimensional transient modelling of the flow and heat transfer in an idealized Trombe wall system was performed for a fixed set of physical dimensions. The governing equations were solved using multiphysics software. Buoyancy and thermal accumulation in a brick wall are the main effects considered. During operation, the solid and fluid temperatures constantly increase, while circulation flow rates, which are significant from the start, show a slow decrease. The room is heated by the parallel mechanisms of buoyancy flow from the collector space and directly by the hot wall, but the latter effect becomes progressively more important. Heat losses through the glazed surfaces of room and collector are of similar magnitude. However, when the wall clearances are closed the collector loss shows an important increase. The role of the typical Trombe wall circulation in the control of heat losses is discussed.