This paper presents results of an experimental investigation of heat transfer and friction for the flow of air in rectangular ducts with repeated chamfered rib-roughness on one broad wall. The aspect ratios of the rectangular duct investigated are 4.8, 6.1, 7.8, 9.66 and 12.0. The roughened wall is uniformly heated while the remaining three walls are insulated. These boundary conditions correspond closely to those found in solar air heaters. The range of parameters studied are: Reynolds numbers from 3000 to 20 000; relative roughness heights from 0.0141 to 0.0328; the relative roughness pitch of 4.5, 5.8, 7.0 and 8.5; and rib chamfer angles of -15, 0, 5, 10, 15 and 18 degrees. The roughness Reynolds numbers corresponding to these parameters range from 5 to 60. Friction factor and heat transfer coefficient correlations have been developed based on the law of wall similarity and heat-momentum transfer analogy.