Air source heat pumps

Air source heat pumps absorb heat from the outside air This is usually used to heat radiators, underfloor heating systems, or warm air convectors and hot water in your home.

• How do air source heat pumps work?
• The benefits of air source heat pumps
• Is an air source heat pump suitable for my home?
• Costs and savings
• Ground source heat pumps
• Find out more

How do air source heat pumps work?

An air source heat pump extracts heat from the outside air in the same way that a fridge extracts heat from its inside. It can extract heat from the air even when the outside temperature is as low as minus 15° C.

Heat pumps have some impact on the environment as they need electricity to run, but the heat they extract from the ground, air, or water is constantly being renewed naturally.

Unlike gas or oil boilers, heat pumps deliver heat at lower temperatures over much longer periods. This means that during the winter they may need to be left on 24/7 to heat your home efficiently. It also means that radiators should never feel as hot to the touch as they would do when using a gas or oil boiler.

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.

Heat from the air is absorbed into a fluid which is pumped through a heat exchanger in the heat pump. Low grade heat is then extracted by the refrigeration system and, after passing through the heat pump compressor, is concentrated into a higher temperature useful 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.
• No fuel deliveries required.
• Can provide space heating and hot water
• It’s often classed as a ‘fit and forget’ technology because it needs little maintenance.
• Can be easier to install than a ground source heat pump, but efficiencies can be lower.

Is an air source heat pump suitable for my home?

To tell if an air source heat pump is right for you, there are a few key questions to consider:

• Do you have somewhere to put it? You'll need a place outside your house where a unit can be fitted to a wall or placed on the ground. It will need plenty of space around it to get a good flow of air. A sunny wall is ideal.
• Is your home well insulated? Since air source heat pumps work best when producing heat at a lower temperature than traditional boilers, it's essential that your home is insulated and draught proofed well for the heating system to be effective.
• What fuel will you be replacing? The system will pay for itself much more quickly if it's replacing an electricity or coal heating system. Heat pumps are not recommended for homes on the gas network.
• What type of heating system will you use? Air source heat pumps can perform better with underfloor heating systems or warm air heating than radiator-based systems because of the lower water temperatures required.
• Is the system intended for a new development? Combining the installation with other building work can reduce the cost of installing the system.

Read more about planning permission for renewable energy technologies

To find out more about whether an air source heat pump is suitable for your home, try the Energy Saving Trust Home Energy Generation Selector tool.

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.

The Energy Saving Trust is currently conducting field trial of ground and air source heat pumps, in order to get a better idea of how they perform, and the saving they achieve, in real life environments. Results will be published in late summer 2010.

To reduce your home's CO2 emissions further, consider installing solar electricity or some other form of renewable electricity generating system to power the compressor and pump.

The Department for Energy and Climate Change (DECC) have announced that the Renewable Heat Incentive (RHI) is expected to be launched in April 2011. It is designed to provide financial support to encourage the uptake of renewable and low carbon heat technologies like heat pumps. It is currently in a planning stage and no final decisions have yet been made by DECC. For more information see the RHI page.

Ground source heat pumps

These systems use similar principles to air source heat pumps to extract heat from the ground.

Ground source heat pumps use pipes buried in the garden to extract heat from the ground. This is usually used to heat radiators or underfloor heating systems and hot water. Although more expensive than air source heat pumps, ground source heat pumps can be more efficient

Find out more

What is suitable for your home?
To find renewable technologies to suit your home, try the Energy Saving Trust energy selector tool.

Technologies
For more information on home energy generation technologies, contact your local Energy Saving Trust Advice Centre on 0800 512 012.

For specific technology questions, visit the Heat Pump Association