Introduction: Air source heat pumps (ASHP) absorb heat from the outside to heat buildings. It is even possible for air source heat pumps to extract useful heat from air at temperatures as low as minus 15°C. For every unit of electricity used to power the pump, 3-4 units of heat are produced, making it an efficient way of heating a building. There are two types of air-source heating systems. Air-to-water systems heat water to provide heating to a building through radiators or an under floor heating system. The other type is an air-to-air system which provides warm air, which is circulated to heat the building.

The benefits of air source heat pumps are similar to ground-source heat systems. Firstly, neither type of system requires the use or storage of external fuel. The systems instead run on electricity, which eliminates the need for a gas connection or storage of oil/solid fuel. Air source heat pumps present an advantage over ground source heat pumps because they require less space to install. Instead of requiring the installation of buried underground coils, air source systems can be fitted using much less space and are therefore, more suited for an urban home.

Benefits of installing an air source heat pump system:

	Air source heat pumps are 400% efficient. This means that for every unit of electricity used to power the pump, 3-4 units of heat are produced.
	Reduces your energy bills. In the past 18 months energy bills have risen by a record 47 per cent and are expected to rise a further 60% by the end of 2008.
	Supplies a comfortable consistent heat to the room.
	Increases the value of the property. Studies suggest a 3% increase, therefore in most cases the system pays for itself.
	Helps the Government meet its objective for cutting carbon emissions by 20% by 2010 as set out in the Climate Change Bill. There will in no doubt be some kind of tax for properties that don’t comply within the near future.
	Require less space to install than ground source heat pumps.
	Reduces your carbon (CO2) emissions.

Suitability:

	You will need space on an external wall outside the property to fit the evaporator coil.
	An air source heat pump should cover the heating requirements of a well insulated property. Due to the lower temperature compared with traditional boilers, it is essential the property is insulated and draught proofed. These measures will lower the heat demand and make the system more effective.
	The only time a heat pump might struggle and require back up from an immersion heater is during extreme conditions such as temperatures below -5 degrees.
	The type of heat distribution system. Air source heat pumps can be used to heat water that is circulated through radiators but under floor heating is more effective due to the lower temperature of the air/water produced. Air-to-air systems require a ventilation system with fans to circulate the warm air.
	Helps the Government meet its objective for cutting carbon emissions by 20% by 2010 as set out in the Climate Change Bill. There will in no doubt be some kind of tax for properties that don’t comply within the near future.

Air to water systems:
In an air-to-water system, the heat produced is used to heat water, which can be used to pre-heat water in a storage tank or circulate through under floor heating or radiators. Heat pumps produce hot water that is a lower temperature (typically 35-45C) than standard boiler systems, which makes under floor heating the most effective option. In an air-to-air system, this heat is used to produce warm air, which is circulated by fans to heat a building.

The efficiency of an air source system is measured by a coefficient of performance (CoP). CoPs for air source systems are comparable with ground-source heat pumps, and generally range between 3 and 4. This means that for every unit of electricity used to power the pump, 3-4 units of heat are produced, making it an efficient way of heating a building. It is even possible for air source heat pumps to extract useful heat from air at temperatures as low as minus 15oC.