Outdoor air is a common heat source for heat pumps, whose limits are well known. However the use of different sources requires additional investment costs. It is then interesting, starting from a given additional investment, on one side to evaluate different compositions for a set of sources and on the other to choose the most favourable source from time to time, according to the building energy demand and the thermal level of each available source. This paper presents a study conducted on the base of a heating system based on multi-source heat pumps. By means of dynamic simulations in TRNSYS, several scenarios were assessed with respect to primary energy consumption in order to define, given an additional budget for the heat pump system, whether it is a good option to invest in ground source or in solar source for the heating systems. The analysis reveals that the most energy efficient solution both for absorption and compression heat pump based systems is to adopt a multi-source system; the ground exchangers should then be sized to allow a minimum ground inlet temperature of-2 degrees C, and the saving in investment cost should be directed to buy solar collectors. (c) 2015 Elsevier B.V. All rights reserved.