A new design of a cost-effective, gridded solar air heater with a high solar to thermal energy conversion efficiency is presented, featuring an increased air to absorber interaction, while still allowing high mass flow rates. We investigate the dependence of this solar air heater’s conversion efficiency as a function of its mass flow rate and find that the efficiency significantly depends on it. Our investigation shows that the conversion efficiency of our solar air heater approaches 80% as the mass flow rate is increased to 0.06 kg/s. As the conversion efficiency depends linearly on the mass flow rate, a significant component of this investigation is the calibration of the anemometer. The findings of this research are based on data taken during both the winter and the summer seasons.