In nearly every country, the building sector plays an important role in total energy consumption. Therefore, the CO2 emissions from the building sector must be significantly reduced if climate neutrality is to be achieved in the long term. If heat pumps are used to supply heat to the large sector of multi-family homes and apartment buildings, it is possible to significantly lower CO2 emissions. The design requirements for the heat pump and the overall system, however, are more complex in these types of buildings than in single-family homes. Specific questions on heating water, the heat transfer system (heat sink) as well as the use of environmental energy at the location (heat source) must be addressed.