For a sustainable market development, transparent and fair product information has to be available for the consumer. In the case of solar collectors, such information can be derived from testing according to a standardized test procedure. For the special situation of solar air-heating collectors the methodology has been revised and extended to align the technical background for product comparison and rating recently. For this kind of solar collector, technical aspects had to be taken into account, which are neglected for solar water-heating collectors in the actual testing standard. This is done because their influence seems to be insignificant. Comparability with water-heating collectors' performance and functionality, as well as within different technical variations of solar air-heating collectors was prepared, by defining a set of parameters describing the collectors' performance. The function tests described in this paper are the result of transferring as many test sequences of water-heating collectors as reasonable and define functional tests to prove the basic function of the collectors under typical operating conditions. As more and more rating procedures and certification issues are coming into focus of industry, these aspects were also taken into account. In the case of performance, rating is mostly dealt with a standardized power output calculation. Although many questions with regard to testing methodologies for solar air-heating collectors have been solved, some more remaining questions are named in the final chapter, to show further research needed.
