A numerical investigation of conjugate convection with surface radiation from horizontal channels with protruding heat sources has been carried out. The flow is assumed to be steady, laminar, incompressible, hydrodynamically and thermally developing. Air is considered as the working fluid. The geometric parameters such as spacing between the channel walls, size of the protruding heat sources, thickness of the substrate and the spacing between the heat sources are fixed. Results are presented to show the effect of parameters such as Re-S, Gr*(S), k(p)/k(f), k(s)/k(f), epsilon(p) and epsilon(s), on the fluid flow and heat transfer. A correlation for the non-dimensional maximum temperature is also developed using the method of asymptotic expansions. (c) 2006 Published by Elsevier Ltd.