Air and source heat pumps

Air heat pumps work in a similar method to ground source heat pumps except they extract heat from air or water as opposed to the ground.

Air source heat pumps are normally fitted outside a house and generally perform better at slightly warmer air temperatures.

How do air source heat pumps work?

The same way that a fridge extracts heat from its inside, an air source heat pump extracts heat from the outside air temperature. Air source heat pumps can work at extremely low temperatures, as low as -15^oC.

There are two main types of air source heat pump system:

• An air-to-water system distributes heat via your wet central heating system. Heat pumps work much more efficiently at a lower temperature than a standard boiler system would. So they are more suitable for underfloor heating systems or larger radiators, which give out heat at lower temperatures over longer periods of time.
• An air-to-air system produces warm air which is circulated by fans to heat your home. They are unlikely to provide you with hot water as well.

Lower temperature heat passes through the heat pump compressor and is concentrated into a higher temperature heat capable of heating water for the heating and hot water circuits of the house.

The benefits of air source heat pumps

• Can lower fuel bills, especially if you are using conventional electric heating.
• Can reduce your carbon footprint: heat pumps can lower your home's carbon emissions, depending on which fuel you are replacing.
• Can provide space heating and hot water
• Can be easier to install than a ground source heat pump, but efficiencies can be lower.
• Little or no maintenance with the 'fit and forget' classification

Costs and savings

Costs for installing a typical system suitable for a detached home range from about £5,000 to £9,000 including installation. Running costs will vary depending on a number of factors - including the size of your home and how well insulated it is.

Savings - will vary depending on many factors, some are outlined below. It is important that the system is controlled appropriately for your needs. Actual savings figures will depend on your exact fuel prices:

• The heat distribution system: If you have the opportunity, underfloor heating often provides greater efficiencies than radiators because the water doesn't need to be heated to such a high temperature. If underfloor heating isn't possible, then use the largest radiators you can.
• Fuel costs: you will still have to pay fuel bills with a heat pump because they are powered by electricity. The saving you achieve can be affected by the price of the fuel you are replacing and the price of the electricity for the heat pump.
• Efficiency of old and new system: the efficiency of the old heating system will affect how much you spent on heating bills previously. If the old heating system was inefficient heating bills could have been high and the difference between the new running costs and the old running costs will be greater, therefore providing a greater saving.
• If the system is providing hot water as well as space heating: the provision of hot water can lower system efficiencies, therefore making running costs higher.
• Temperature setting: if you heat your home to much higher temperatures with a new heat pump system than you did with an old heating system then your home will be warmer, but heating bills will be higher than if you continued with the same heating pattern. It's a good idea to set thermostats to around 18 to 21 degrees centigrade.
• Using the controls: learn how to control the system so you can get the most out of it. Your installer should explain to you how to control the system so you can use it most effectively.