The paper deals with a numerical simulation of natural convection flows in asymmetric triangular cavities, submitted to a uniform heat flux from below when inclined sides are maintained isothermal. The aim of the study is to examine the influence of inclined sides' dimensions on thermal and dynamic fields. An aspect ratio is defined in relation with the title angle. The two dimensional flow equations, expressed in a stream function-vorticity formulation, along with the energy equation are solved using the control volume finite element method. Such a configuration is encountered in solar energy systems, where natural convection in the enclosed fluid due to vertical temperature gradients between a black bottom and a transparent cover plays a decisive role. The numerical solutions provide information on the thermal exchange sensitivity to two governing parameters: the Rayleigh number and the aspect ratio in a basin still. Results can be constructive for design optimizations in energy systems such as solar water distillers and air conditioning process.