This article reports an experimental study of free convection in an inclined rectangular channel open ended at various aspect ratios. The upper plate is heated by a uniform constant heat flux while the lower plate is attached to a radiant barrier. The channel width and length are 0.7 and 1.5 m, respectively. Tests were made for different aspect ratio ( air gap to channel length, S/L) by varying air gap space and different constant heat fluxes. The tilt angle was fixed at 15 degrees. The objective is to determine the heat transfer coefficient and the induced airflow rate. The correlation equations of Nusselt and Reynolds numbers as function of Rayleigh number and aspect ratios are also developed to evaluate the heat transfer coefficient through the channel. The correlationships are valid in the range 1 x 10(5) < Ra sin 15 < 1 x 10(8). Heat transfer enhancement due to the radiant barrier was assessed by comparison to a channel equipped with gypsum board.