This study reports an experiment to investigate the feasibility of a passive heating roof-pond system on an existing room in the cold winter conditions of Riyadh, Saudi Arabia. Statistical analyses of data recorded during the winter season of 1996–97, are carried out to evaluate the thermal peformance of the proposed system. Total effective heating and the heating power of the roof pond system are computed and analysed. Results indicate that the roof-pond system is capable of maintaining warm indoor air temperature conditions. The statistical formulae for this system are presented and used to estimate the indoor daily average air Dry Bulb Temperature (DBTAvg-indoor] created by the system. Validation of the proposed formulae is also presented.