In this study, the thermal performance of the single and double pass solar air heaters with normal glazing and with quarter perforated cover was investigated experimentally. The solar air collector was tested with two different perforated covers in which the holes made on one cover had the center-to-center distance of 20D (6 cm) and on the other cover it was 10D (3 cm), where D (0.3 cm) was the hole diameter. The air mass flow rate was varied between 0.011 kg/s and 0.037 kg/s. The efficiency of the double pass was always greater than the single pass air heater by 5-22.7% for the same air mass flow rate. At mass flow rate of 0.037 kg/s, the average efficiency of single and double pass air heaters with normal glazing were 49.98% and 53.67%, respectively. It was found that, the efficiency of the air heater with 10D perforated cover is slightly higher than the one with 20D perforated cover for both single and counter flow collectors. The average efficiency of single and double pass solar air heaters with 10D perforated cover were 46.40% and 54.76%, respectively, at mass flow rate of 0.032 kg/s while at the same mass flow rate, the average efficiency of single and double pass air heaters with normal glazing were 49.36% and 51.70%, respectively. (C) 2014 Elsevier Ltd. All rights reserved.