Providing artificial roughness on the air flow side is an effective technique to enhance rate of heat transfer in solar air heaters, which results in associated higher value of friction factor, and more power required. A novel solar air heater duct with three artificially roughened sides has been analyzed (Prasad et al., 2014), for more increase in heat transfer than that in only one side roughened solar air heaters. Artificially roughened solar air heaters have been analyzed (Prasad and Saini, 1991) and investigated (Verma and Prasad, 2000), for optimal thermo hydraulic performance. The present analysis deals with optimization of therm hydraulic performance in three sides artificially roughened solar air heaters, and arrives at the conclusion that the equation given by e(opt)(+) = e/D root(f) over barr/2Re = 23, always corresponds to the optimal thermo hydraulic performance, when every set of the values of the roughness and flow parameters p/e, e/D and Re, separately or combined, results in the optimal therm hydraulic performance. Optimal thermo hydraulic performance of such solar air heater is both quantitatively and qualitatively better than one side roughened solar air heaters. (C) 2014 Elsevier Ltd. All rights reserved.