AbstractWe present results from a field study of a heat pump domestic hot water heater. The data demonstrate that the system was able to maintain a high standard of hot water service to all participants and in some cases actually improved the standard. The heat pump was able to realize annual average savings of 50–58 per cent when compared to conventional resistive water heaters. We also show that, in New Zealand, large scale application of this type of heat pump should become an economic alternative to the construction of new electrical generating capacity in the 1990