Since the end of 1979 every other day an electrically operated heat-pump has started operation in Berlin (West). Pros and cons of heat-pumps are a much discussed subject. But what is the opinion of the user. As it is not known the BEWAG carried out a written customer inquiry in the summer 1982. The aim of the inquiry was to improve the advisory service by means of the answers obtained, to obtain information about the reliability or liability to defects of the heat pump, the mechanism they operate on and to know how big the oil substitution potential is. Customer satisfaction with the heat pumps was a further point of interest.