The authors present a new calculation code using a two-dimensional finite-element method valid in permanent and laminar flow. They consider elements of symmetry existing in boundary conditions imposed on velocities as well as on temperatures, then elements of symmetry existing only in boundary conditions imposed on velocities and, finally, boundary conditions containing no symmetry. The flow is two-cellular so that the Rayleigh number remains inferior to a value in the order of 10(6). Beyond this value, secondary cells can appear, following the geometry of the enclosure.