Design and thermal control of tilted channels in air natural convection requires knowledge of relations between process parameters. Composite correlations of average Nusselt number in terms of channel Rayleigh number (10 less than or equal to Ra less than or equal to 9.0 x 10(4)) are proposed for inclined channels,vith uniform symmetric or asymmetric heat flux. The thermal radiative effects are taken into account in modified Nusselt and Rayleigh numbers. The surface emissivities considered are 0.05 and 0.8. Experimental data employed to obtain the proposed correlations are in good agreement with the correlations for a vertical channel from published literature. Composite correlations between Nu and Ra cos theta valid in the whole range 0-85 degrees of the inclination angle are given. Moreover; a general composite correlation is proposed for all heating modes, in which the inclination angle is in the range 0-85 degrees and for surface emissivity nor greater than 0.8. Recommendations for the thermal design of single or multiple channels are given.