Using passive systems or solar energy for space cooling is highly conditional upon the heat transfer potential between the building components and the interior space. This paper presents a simplified theoretical model that describes the evolution of temperature in a room that is cooled by a chilled ceiling in the presence of a heat source on the floor. Using arguments of dynamic similarity, the theoretical model is confirmed with scale-model experiments run in a rectangular tank. The scale model uses a metallic heat exchanger to simulate the chilled ceiling and an electric heater as the heat source. The greatest heat transfer from the fluid towards the ceiling occurs immediately with the simultaneous activation of the heater and the chilled ceiling. As time elapses and the heat transfer decreases, the room cools more slowly and its temperature tends asymptotically towards equilibrium. This is achieved when the heat loss through the ceiling equals the heat supply from the heat source. The theoretical model can predict when a chilled ceiling, acting as transient a heat sink, will achieve a comfortable temperature in a room with an internal heat source. (C) 2011 Elsevier Ltd. All rights reserved.