Solar heat in solar thermal combisystems is usually used via a buffer storage. Alternatively, the solar collectors may be connected directly to the space heating circuit in order to store the heat in the building itself. Such a direct solar integration is investigated within system simulations for different layouts and heating elements. The operation of these systems requires a control strategy, which distributes the solar heat optimally between the potential heat sinks leading to the lowest overall energy consumption. This way a solar fraction may be achieved which is comparable to usual combisystems equipped with a three times larger buffer storage. A prototype of one of the investigated heating concepts within a single family house proofs the functionality of the system concept and the high solar yield, particularly at low radiation levels. The direct solar heating increases the solar fraction of combisystems significantly or alternatively decreases the necessary storage volume considerably if a certain system performance is desired. (C) 2016 Elsevier Ltd. All rights reserved.