Experimental and numerical investigations of vertical mantle heat-exchangers for solar domestic hot-water (SDHW) systems have been carried out. Two different mantle inlet positions are investigated. Experiments based on typical operation conditions are carried out to investigate how the thermal stratification is affected by different positions of the mantle inlet. The heat transfer between the solar collector fluid in the mantle and the domestic water in the tank is analysed by CFD-simulations. Furthermore, side-by-side laboratory tests have been carried out with SDHW systems with different mantle inlet-positions. It is shown that for a high inlet-temperature to the mantle, it is an advantage to have the inlet located at the top and for a low inlet temperature it is an advantage to have the inlet moved down. Marketed tanks have typically the mantle inlet located at the top of the mantle. The side-by-side laboratory tests indicate that it is an advantage to move the inlet down front the top. (C) 2003 Elsevier Ltd. All rights reserved.