Only a few metres below the ground the temperature stays at around 11-12°C throughout the year. Using ground source heat pumps (GSHP), this heat can be sourced to provide space heating in your home, and in some cases help pre-heat your water for your central heating system.

There are three key elements in a GSHP:

•  Ground loop: lengths of plastic pipe buried in the ground either vertically (borehole) or horizontally (trench). This is a closed circuit of water and anti-freeze or refrigerant pumped around the pipe absorbing heat from the ground.

•  Heat pump: this is an electric pump, working in the same way as the one in your refrigerator, using the condensing and evaporation of a refrigerant to move heat from one place to another

•  Heat distribution system: consists of under floor heating or radiators for space heating and water storage for hot water supply. Some systems can also be used for cooling in the summer.

GSHPs are a very efficient method of low grade heating; for every 1 kWh of energy used to pump the fluid around the system, 2.5-4kWh of heat are produced. If coupled with a renewable electricity generator, the system becomes essentially carbon neutral.

The spacing heating systems that are required with such a system - under floor heating - are generally more comfortable for the user as well as being more efficient than 'traditional' radiator systems. GSHP systems bring with them large reductions in carbon dioxide emissions compared to a conventional heating system, especially an electric system.

GSHPs are not visible once installed and require minimal maintenance.

A large open area is required in order to lay the trenches although they can be buried under a car parking area. Retrofitting of such systems rarely happens, as under floor heating is difficult and expensive to fit into an existing building. An extensive ground survey is required before the suitability of a technology to a certain site can be ascertained.

For a professional installation of a GSHP, you should expect to pay somewhere between £800 and £1200 per kW of peak heat output, which does not include the cost of the distribution system. Trench systems tend to be at the lower end of the range, boreholes at the higher end. GSHPs are often cheaper to run (fuel wise) than oil systems or electric storage heaters. They are, however, more expensive than mains gas.

Please email or call CEN on 020 8683 6694 for further information or advice.