From Renewable Heat
An air source heat pump extracts heat from the outside air in the same way that a fridge extracts the heat it generates inside. Even cold air is full of energy and ASHP uses the freely available heat in the ambient air to provide efficient heating and hot water at temperatures as low as -25˚C. As air is abundantly available all around us, ASHP has the advantage of low installation costs and minimal space requirements. The relatively mild winter temperatures in the UK mean excellent levels of efficiency and performance are achieved throughout the year. There are two main types of ASHP, air-to-water and air-to-air systems. An air-to-water system distributes heat via a wet central heating system, using water for the heat transfer. An air-to-air system produces warm air that is then circulated by fans to heat the property.