This study deals with natural-convection heat transfer from a vertical electrically heated plate, which is symmetrically placed in a chimney of variable height. The heated plate serves as a thermal pump for ventilation of a symmetrical enclosure beneath the chimney. In order to provide a comprehensive picture of the phenomena, three main approaches are used in parallel: temperature and velocity measurements, flow visualization, and numerical simulation. Temperature measurements are done by thermocouples distributed inside the plate and through the chimney. Velocity measurements are performed by means of a precise anemometer. Visualization is performed using smoke of incense sticks, with video recording and consequent image processing. Computer simulations of unsteady flow and temperature fields are performed in 3D and compared with measurements and visualization, with special attention paid to velocity fluctuations. Analysis is presented on the dependence of the temperature distribution on the flow field. The air flow rate on the heating plate in the chimney increases with the chimney height and is adequately predicted by the numerical simulation of the system.