A mathematical model describes the dynamic thermal behaviour of a baffled solar air heater is presented. The transient behaviour of the heater results from sudden changes in the intensity of the incident solar radiation and the inlet fluid temperature. In terms of the presented model, analytical solutions for the fluid and solid domains are derived. Also, expression for the thermal efficiency of the heater is presented. The effects of different design parameters on the thermal performance of the heater are investigated. The validity of the theoretical model is verified experimentally where it is found that both theoretical and experimental results are in a good agreement.