An experimental study of buoyancy-driven convection in rectangular enclosures has been made in order to obtain convection coefficients and data correlations which are more accurate for real building situation. Three different flow regimes viz. stably-stratified flow, buoyancy-driven vertical flow and horizontal flow were investigated. The Nusselt number variation with respect to the Rayleigh number has been plotted and compared with existing correlations, In general, the measured data were lower than the data obtained from the existing correlations which are mainly derived from data obtained from experiments involving isolated surfaces.