This paper compares the performance of configurations of solar heating combitank systems, which are designed to provide both space heating and domestic hot water (DHW), using a specially designed six-day test. The test sequence is applied to every tank with the same boundary conditions, so that the results, in the form of solar fraction, can be used for direct comparisons. The six days of radiation data were chosen after an analysis of the summer insolation data for Borlänge, Sweden, and are representative for the summer period in Sweden. The systems are tested with a purely DHW load with no space heating load. The solar collector is emulated using a collector hardware simulator (CHS). Sixteen combitank systems have been tested with the resulting solar fraction from the six-days ranging from 52% to 93%. This paper describes the test procedure, the tested systems, the results from the test and gives conclusions that can be drawn from a detailed analysis of the measured data.