After turning on a room heating system (e.g. central heating) a thermal transient phenomenon takes place on the wall}room system, until it reaches a "nal thermal equilibrium state. The temperature pro"les on the wall cross-section, starting from an initial pro"le, corresponding to the initial thermal equilibrium state, come gradually through successive intermediate temperature pro"les, to a "nal temperature pro"le corresponding to the "nal thermal equilibrium state. These intermediate, nonlinear and time-dependent temperature pro"les characterize the wall thermal transient state and describe the dynamic thermal behaviour of the wall}room system. The mass of the air in the room is negligible, compared to the mass of the surrounding walls, so the dynamic behaviour of the room}wall system is imposed by the corresponding thermal dynamic behaviour of the walls. The in#uence of this thermal transient state is important for the room heating behaviour because it acts as a thermal #ywheel attenuating and smoothing the room temperature variations. In the present work, using the integral method, analytical expressions yielding the temperature pro"les, and the duration of the transient state as a function of thermal and structural characteristics have been developed. Conclusions were drawn on the dynamic thermal behaviour of the room}wall system.