The aim of the project is to compare different methods used for testing small solar domestic hot water tanks. A small hot water tank is tested at three different European laboratories by means of the test methods normally used at the laboratories. The tank is marketed in Denmark.The test carried out at the Department for Buildings and Energy compromises determination of the heat loss coefficient for the tank and the heat transfer coefficient for the auxiliary helix. A dynamic test is performed and a simulation model of the tank is made and validated against measured energy quantities and temperatures. The annual thermal performance for a solar domestic hot water system based on the tested tank is calculated. Further, proposal for a future test on mixing during draw-off as well as proposal for a maximum acceptable mixing during draw-off is given.