Natural and mixed convection in air in an inclined channel with the lower wall heated at uniform heat flux and in the presence of an obstacle either at the entrance or exit of the channel is investigated experimentally and numerically, respectively. The study is accomplished for several heat fluxes. In mixed convection the Reynolds number is equal to 150, this being in the laminar regime. Natural convection investigation is carried out with Rayleigh number equal to Ra=6.68x10 5 and 2.67x10 6 . The effect of the obstacle disposition and height is investigated by flow visualization and wall temperature distribution.