John Cantor studied mechanical engineering and started his working life in the refrigeration industry. A keen environmentalist and practical engineer, he became interested in heat pumps in the early 1980s and subsequently designed and built three ambitious projects heating community swimming pools at Lazonby, Greystoke and Askham, which were still operating well over twenty-five years later. Since then, he has installed many different systems and this has provided him with a wide and varied range of experience. He was a heat pump inspector for the first round of government Clear Skies grant initiatives, has tutored a number of heat pump courses, has written many articles on the subject, and now spends much of his time as an advisor and consultant. Gavid D J Harper is the author/co-author of a number of books including Domestic Solar Energy (Crowood, 2009) and Small-Scale Wind Power Generation (Crowood, 2010). He writes extensively on sustainability issues and is currently researching the subject of reen business models for sustainability for a PhD at Cardiff University Business School. Gavin is a member of the Institute of Engineering and Technology, and holds two honours degrees from the Open University and three masters degrees.