This paper presents the results of a life cycle assessment of domestic heat pumps in the UK in comparison with gas boilers. The study considers air (ASHP), ground (GSHP) and water (WSHP) source heat pumps. The results show that heat pumps have higher environmental impacts than gas boilers due to the use of electricity. On average, the impacts for the ASHP are 82% higher than from the boiler and 73% for the GSHP and WSHP. The exception to this are the global warming, fossil resource depletion and summer smog impacts which are lower for the pumps than the boilers. For example, up to 36% of CO2 eq. can be saved with the WSHP and 6% with the ASHP in comparison with the boiler. Among the heat pumps considered, ASHP have the highest impacts due to lower efficiencies and higher material requirements for the system. The GSHP and WSHP have comparable impacts, with the latter being marginally better. The life cycle impacts of heat pumps may improve if the UK electricity mix is sufficiently decarbonised; however, they will still remain higher than for the gas boiler. Overall, their potential to contribute to the UK climate change targets is limited. (c) 2012 Elsevier Ltd. All rights reserved.