In this study, a double glass and double pass air heater powered by solar energy has been studied numerically. Time-dependent energy balance equations were integrated by fourth order Runge-Kutta method. The temperature of air at outlet, thermal efficiency and thermohydraulic efficiency of the heater were calculated for various channel depths (D = 1 similar to 7 cm) and air mass flow rates (m = 0.01 similar to 0.2 kg/s). As a result of simulations, it was found that the heater thermal efficiency increases and temperature of air at outlet decreases with increasing air mass flow rate. It was also observed that the daily average thermal efficiency of the heater decreases %5 similar to 19 with an increase in the depth of the air duct from 1 to 7 cm. According to the results obtained, the optimum channel depth of the double pass solar air heater was calculated 4 cm for the maximum thermohydraulic efficiency (eta(TH) = 0.6689).