The fluid flow and heat transfer induced by natural convection in an infinite horizontal channel containing an indefinite number of uniformly spaced rectangular blocks on its low er wall (repetitive geometry) is studied numerically. The blocs are heated at constant temperature T-C’ and connected with adiabatic surfaces. The upper wall of the channel is maintained cold at a temperature T-F’(T-F’ < T-C’). The working fluid is air (Pr = 0.72). The parameters governing this problem are the Rayleigh number (10(2) less than or equal to Ra less than or equal to 5 x 10(6)) and the relative height of the blocks (1/8 less than or equal to B = h/H less than or equal to 1/2). The effect of the computational domain choice on the multiplicity of solutions is studied. The effect of each solution on the flow and the heat transfer is examined, This investigation shows that the symmetry of the flow is not always maintained although the boundary conditions for this problem are symmetrical, For given ret of the governing parameters. the difference between two multiple solutions in terms of the heat transfer may reach 25%,