The rule of thumb for a horizontal collector loop for a house meeting current building regulations is that a minimum area of land twice that of the floor area of the property will be required to bury the collector loops. The exact amount will depend on a number of factors including soil type, heating requirements of the home and how wet the ground is.
Sizing the ground loop is just as critical as calculating the heat load of the house. If there is insufficient ground collector, or too much heat is extracted from the ground there is a danger of a vicious circle being created with the ground source heat pump working harder to extract heat from the cooling earth making it less efficient and increasing running costs. The ultimate result is the ground will freeze and the ground source heat pump fail.
Where there is not enough ground for a horizontal collector it is possible to collect heat from boreholes. These are slightly more efficient than horizontal collectors but drilling can be expensive.
Other options for collecting heat exist from water source collectors or “open-loop” collectors from subterranean aquifers, lakes or rivers.