It works in a very similar way to a domestic refrigerator, utilizing working fluid driven around a refrigerant circuit containing four components - an evaporator, a compressor, a condenser and an expansion valve. The refrigerant liquid circulating within the system has a boiling point -40c and evaporates when absorbing heat from ambient air. This means it"s possible to extract considerable heat from extremely low temperatures. The resulting refrigerant gas is then compressed, adding more heat energy and raising its temperature to around 60c. This is then passed via the heat exchanger into your home for use in your hot water cylinder and central heating. This product consists solely of one neat, compact unit, complete with refrigerant that can be easily installed in a loft space or externally and quickly plumed into your existing system. The co efficiency of performance or COP of a heat pump is the ratio of the output heat to the input supplied. An air source heat pump operating at COP 3.4 will provide 3.4kW of heat output for very 1kW of unit input (energy consumed). The COP of heat pumps seem to compare very favorably with high efficiency gas appliances (90% -95% efficient), and electric heating (100%), but the full costs of energy consumed must be considered, energy from gas is typically much less expensive than that from electricity at the moment. However, a heat pump of COP 3.4 such as in the example above could be less expensive to use than even the most efficient gas appliance. The air to water systems are ideal where solar thermal cannot be fitted or the property has no gas.