A ground source heat pump circulates a mixture of water and antifreeze around a loop of pipe – called a ground loop – which is buried in the garden. Heat from the ground is absorbed into this fluid and is pumped through a heat exchanger in the heat pump. Low grade heat passes through the heat pump compressor and is concentrated into a higher temperature useful heat capable of heating water for the heating and hot water circuits of the house. Ground loop fluid, now cooler, passes back into the ground where it absorbs further energy from the ground in a continuous process while heating is required.

The length of the ground loop depends on the size of your home and the amount of heat you need – longer loops can draw more heat from the ground, but need more space to be buried in. Normally the loop is laid flat, or coiled in trenches about two metres deep, but if there is not enough space in your garden you can install a vertical loop down into the ground to a depth of up to 100 metres for a typical domestic home.

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. Your garden doesn’t have to be particularly large, but the ground needs to be suitable for digging a trench or a borehole and accessible to digging machinery This is more efficient for Underfloor heating systems, larger radiators or low temperature fan convectors (warm air heating) can perform better than standard radiator-based systems because of the lower water temperatures required.