Until a few years ago, solar air heating collector systems have received only limited attention on the market compared to fluid heating collector systems. Solar air heating collectors are more difficult to measure and to evaluate. This not only hinders the development of new products but also provides less transparency on existing products. In the meanwhile, a more detailed measurement method has been incorporated into the test procedure for solar thermal collectors (DIN EN ISO 9806). On this basis, Fraunhofer ISE created an MS Excel application in order to improve air collector evaluation and system planning. The calculated results serve to certify solar air collectors according to Solar KEYMARK, to design system layouts, to develop air collectors as well as to perform parameter variation studies.