The present study deals with laminar natural convection flow in a vertical open-ended channel bounded by isothermal walls. A numerical investigation has been performed to estimate the effect of the channel width and wall-to-ambient temperature difference on natural convection heat transfer and induced flow rate. The results have been obtained for Pr of 0.7, of (0.01 to 0.30) and of (101 to 108). Different correlations are deduced to relate each of Nusselt number, flow velocity, flow temperature, thermal entrance length and Reynolds number with modified Rayleigh number and the width-to-length ratio of the channel. Temperature and velocity distribution are potted at different heights along the channel.