The aim of the project is to determine a maximum acceptable mixing rate during hot water tappings, so called draw-offs. Based on a pervious proposal for a maximum acceptable decrease of thermal performance due to mixing during draw-off, investigations are carried out in order to determine the mixing rate corresponding to the maximum acceptable decrease of thermal performance. However, the thermal performance is depending on several different factors such as solar collector area, hot water tank volume, daily hot water consumption etc. Therefore the method first proposed is not very suitable. Instead a different tank test is proposed. It is proposed to use a draw-off test where the energy tapped, from a uniform heated tank, from the start of the draw-off until the volume of the domestic water in the solar tank has been tapped must not be smaller than a certain percentage.