Heat pump systems can easily replace fossil fuel boilers, such as oil or coal, or electric fired boilers. If the heat is distributed through radiators then the hot water output can be fed directly into wet radiator systems. If heat distribution is by warm air, then heat pumps can produce this heated air directly.

The golden rule is to size the heat pump so that it produces about 90% of the required heat output, and for the really cold months to use an additional heat source such as electric radiator or wood fire.

For typical ground conditions and typical family homes, the length of collector pipe for ground source heat pumps will vary between 30 m for 3 kW heat output and 100 m for 10 kW. The collector pipe may be either laid in a horizontal trench or vertically by inserting into a specially drilled bore hole. The drilling of a bore hole requires access for a drilling rig whilst for a horizontal trench one needs access to a garden or open space.

The horizontal trench needs to have sufficient depth so that the ground temperature is not influenced to any extent by the ambient air temperature. In middle Europe, 0.9 m will suffice whereas in Northern Europe 1.2 m or even 1.5 m may be required.

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