The efficiency of the solar air collector can be enhanced by using metal vanes which are attached between the absorber and bottom plate of the collector. A mathematical model and solution procedure to study the effect of the metal vanes are presented. A method to select an optimal number of metal vanes, as well as an appropriate depth for the flowing air duct, has been developed. Moreover, a comparison between the performance of a collector having a box frame absorber and one having a finned plate absorber was carried out. The results show that a high efficiency can be achieved with the use of the metal vanes, particularly at smaller depths of the air duct.