The buffer tank avoids frequent starts and stops of the burner in a boiler installation and is thereby contributing to increasing the service life of the boiler and reducing its harmful emissions. The buffer tank also stores an adequate volume of energy that allows an instant supply of sufficient flow to the water heaters in each flat during peak load intervals. The buffer tank is then loaded to the desired supply temperature for the distribution system. In principle, the buffer tank is not required for a large number of flats as the entire piping system and the larger boilers will provide a sufficient buffer volume to accommodate the large load changes in domestic hot water use. The actual limit will depend on the volume in pipes and boiler as stated previously, but it does also relate to the boiler load.