A general numerical method for the solution of the complete 3D averaged Navier-Stokes equations is presented. This method uses nonorthogonal co-ordinates, Cartesian velocity components and a pressure-velocity-coupling algorithm suitable for nonstaggered grid systems. A k-e two-equation turbulence model is used with this method to calculate the turbulent flow inside a heated space in communication with the outside environment through two small ventilation openings.