A mathematical model for predicting thermal efficiency, heat gain, and outlet air temperature of a covered plate attic solar collector under steady conditions was developed. The model presented in this paper utilizes the basic principles and relationships of heat transfer to simulate the behavior of the solar air heaters under various conditions. The model was validated by comparing the predicted outlet air temperatures and collector efficiencies to those measured during drying operation of an attic solar collector. The effect of the air speed inside the collector and wind speed above the collector on the collector efficiency were investigated using the mathematical model. (C) 2003 Elsevier Ltd. All rights reserved.