Due to an increased insulation rate and more energy efficient ventilation systems, the production of domestic hot water (DHW) is growing in importance in the overall heat demand of residential buildings. The selection of a DHW-system with a high production efficiency is therefore important to reduce primary energy use in buildings. Besides selection also a proper use, including adequate sizing and control strategy, will have a positive effect on overall production efficiency. In a recently executed research project, funded by the Flanders government (IWT), the selection and sizing instructions for domestic hot water installations are being revised. Hereby, a large attention is paid to the actual hot water demand or DHW tap patterns. These tap patterns are gathered by a large number of detailed measurements and simulations. To deal with this enormous set of data, a methodology to characterize tap patterns is needed to generalize the results which are achieved in this project. Clearly, this characterization depends on the purpose for which it will be used. First, a methodology to size production units based on tap patterns is presented and illustrated with a number of measurements and elaborated case studies. The basic idea behind this methodology is that the tap pattern will be characterized by the maximum demand within a time step and this for different step sizes. This approach allows to present an overview of possible topologies, which will all meet the net heat demand of the selected case study at an any time. Afterwards to present some guidelines towards selection, the influence of tap patterns on different topologies is discussed. This discussion is funded with some lab tests executed according to the recently induced Ecodesign regulations. As a result of these considerations, some guidelines to optimize sensor positioning within storage tanks are presented and an evaluation is made regarding the applicability of the Ecodesign labeling within energy performance calculations for buildings.