This work analyses, from an energy performance point of view, the potential and constraints of heat pump (HP) heating systems in new and existing multifamily (MF) buildings. It starts by a monitored case study of an innovative solar and HP system implemented in a new MF building. Then, and via numerical simulation, the potential of this particular system is analysed for 6 different MF building heat demands, followed by a comparative analysis of the potentials and constraints of 6 different heat sources for those building demands. Finally, the potential impact of a generalised development of these types of systems in Geneva's MF building stock is discussed in terms of annual electricity consumption and daily peak loads.