In this paper, the thermal efficiency of a solar air collector called unglazed transpired collector (UTC) has been investigated both experimentally and numerically. Experimental investigations were carried out in a laboratory with a controlled environment. Measurements of temperatures, air velocity and irradiance were performed for three air mass flow rates, three distinct irradiances and two plenum thicknesses. Perforations in the form of slot were selected to enable a comparison with 2D numerical simulations. Meanwhile, a commercial finite volume software was used to model the heat transfer and air flow through the collector. The CFD simulation shows good agreement with experimental results. It was found that a weak heat exchange process took place in the plenum: the maximum efficiency difference between the two plenum thicknesses (5 and 15 cm) was only 3.25%. (C) 2013 Elsevier Ltd. All rights reserved.