In the present study, solar air heater duct roughened with non-uniform cross-section saw tooth rib has been numerically investigated for Nusselt number and friction factor. The investigation has been carried in 3-D with computational fluid dynamics software. The parameters, Reynolds number and relative roughness pitch ranged from 3000 to 15000 and 4 to 30 respectively. The relative roughness height and saw-tooth angle were 0.043 and 45 degrees respectively. The renormalization group (RNG) k-epsilon turbulence model was selected for analysis. At relative roughness pitch of 16, both the Nusselt number and friction factor were maximum for the investigated Reynolds number range. The contours of turbulent dissipation rate, turbulent kinetic energy, static temperature and static pressure have also been plotted. The maximum Nusselt number and friction factor enhancement over smooth duct was 2.18 and 3.34 respectively at Reynolds number of 15000 and relative roughness pitch of 16. (C) 2017 Elsevier Ltd. All rights reserved.