Building Energy Simulation (BES) programs commonly employ a coupled multi-zone thermal and airflow network modelling approach to evaluate the natural ventilation in buildings. However, the robustness of such thermal-airflow models needs greater scrutiny. In particular, the method for determining the indoor-floor surface convective heat transfer coefficient (CHTC). In an attempt to make an initial investigation on this problem, this work utilized Computational Fluid Dynamics (CFD) for numerically examining the heat transfer and flow-fields in a typical room with a single sided window. While doing this, the convection heat transfer on the indoor floor surface driven by a thermal buoyancy effect established due to a temperature difference between inside surface of the floor and outside ambient was examined. The result showed that the heat transfer behavior of this partly open room was strongly influenced by the Rayleigh number (Ra) and the Window Opening Fraction (WOF). Further, it was found that the heat transfer on the floor varied significantly in a spatial context within the floor. As such, there is a significant scope of increasing the robustness of thermal models of naturally ventilated buildings by greater utilization of empirical relationships developed particularly for this purpose.