A buoyant driven flow of air an infinitely long enclosure with a uniformly heated wall was numerically investigated. A 2-dimensional, laminar, steady and in compressible flow was considered and the effect of varying the aspect ratio (AR=L/W) of the enclosure and continuity,momentum and the energy equations simulating the flow were solved by the finite volume method. The phenomenon of natural heat convection is applied in the electronic industry for cooling heat-generating electronic systems, in the agriculture sector for drying and preservation of agriculture, natural produce and for even distribution of heat in greenhouses. In architecture, natural heat convection is applied for thermal insulation of buildings. Results on the velocity profiles established that buoyancy occurred and there was flow of hot air to the upper part of cavity constituting the primary velocities. There was also flow of air towards the free stream constituting the secondary velocities. For all AR and GR values the primary velocities decreased smoothly untill a critical velocity was attained then the flow become streamlined. Increase in Gr values increases the rate at which the critical velocity is attained. Increase in AR raises the value of critical velocity required for a flow to become stream lined. Secondary velocities increases smoothly until a maximum velocity is attained then the flow become streamlined for all AR and Gr values. Increase in AR values lowers the maximum velocity reached for a flow to become streamlined. For all AR values the maximum velocity component was high for higher Gr values. The primary and secondary velocity profiles are more streamlined for AR values beyond one. This increases with increase in AR. Results on the temperature profiles showed that increase in Gr leads to a substantial exchange of hot air from the hot region to the cold region making temperature profiles more skewed. Increase in AR makes the profiles more evenly distributed leading to an even distribution of temperatures.