We have studied a type of hot air generating solar collector. The experimental work led us to study the variation of DeltaT = T-abs - T-a with the total solar radiation E received by the collector. We defined a linear domain characterized by a linear correlation between DeltaT and E. This linear correlation led us to describe the collector by using two characteristic temperatures TL and TG We also introduced two standard solar radiations, Eo and E-L We then used the four parameters TL, TG, EL and Eo to build a model to calculate the maximum efficiency of the collector eta (m), the maximum useful heat gain q(um) and, what we called, an utility factor F-u. We noticed a good agreement between the experimental values of eta (m), q(um), and those calculated from the model. Moreover, the description of the model led us to study the product Delta TE and its variation with E. We saw that the maximum Value of Delta TE corresponds to the maximum value of the useful heat gain q(u). We then investigated another function E-H which is related to the full capability of heating of the absorber when it operates under a particular solar radiation condition. (C) 2001 Elsevier Science Ltd. All rights reserved.