AbstractThis paper presents an investigation of the performance of single and double exposure solar air heaters. A conventional solar air heater consist of a flat passage between two metallic plates through which heating fluid (air) is made to pass. the conduction loss along the lengths of the plates in the direction of the air flow and the radiation loss of heat from the absorbing plate to the bottom plate have been incorporated in the analyses. the analyses consist of the exact solutions of the heat balance equations for the absorbing plate, bottom plate and the air stream. Analytical expressions for the plate and the air stream temperatures as a function of distance along the direction of air flow and some other parameters have been derived. It is found that the heat conduction effects are negligible in both the air heaters and the reradiation of heat from the absorbing plate to the bottom plate is also insignificant.