In recent years, heat pumps have emerged as a promising new form of technology with a relatively low environmental impact. Moreover, they have presented householders with an opportunity to reduce their heating bills. Heat pumps can heat a building by "pumping" heat from either the ground or the air outside: an intriguing process which utilizes principles that are somewhat analogous to those employed in the domestic refrigerator. This book describes what a heat pump is, how it works, the different methods of pumping heat, and the importance of an appropriate and well-planned installation. It examines the air, the ground, and water as sources of heat and explains how to make an informed choice; considers the all-important subject of distributing the heat through radiators or through an under-floor system; covers hot water production and delivery to the taps; outlines environmental and financial issues associated with heat pumps; dispels common misconceptions; and presents a number of case studies.