Today many factors affect the fluids that are being selected for use in domestic and commercial heat pumps. These include environmental issues, system cost and efficiency and several papers have been written to promote and discredit hydrofluorocarbon against natural (hydrocarbon) fluids as the best replacement for R22. This paper attempts to resolve this issue in terms of the environment. energy efficiency and system costs for small domestic and commercial heat pumps. Copyright (C) 2001 John Wiley & Sons, Ltd.