This work describes the results of a numerical study of buoyancy-driven flow in a stairwell model. Direct comparisons with the experimental data have been presented. The model is based on the conservation equations of mass, momentum, and energy and the transport equations of turbulence energy and its rate of dissipation. Two different wall thermal boundary conditions, namely, temperature and heat flux, are used and the results are compared. In the case of the heat flux boundary condition, only the convective component of the heat flux at each wall has been used, by first calculating the radiative component and then separating it from the total heat flux. The numerical model predicts the overall features of the flow satisfactorily, and the details of the velocity and temperature field with reasonable accuracy.