Ground Source Heat Pumps

A ground source heat pump collects heat from the ground through fluid in buried pipes, either in shallow horizontal trenches or in deep vertical boreholes, and then lifts that heat for radiators, underfloor heating and hot water. Ground temperature a metre or two down changes far less through the year than air temperature, so the system avoids the coldest-air penalty that air source units face. That steadier source is its main attraction, and the ground works are its main cost and complication.

The choice between trenches and boreholes depends on land area, soil and rock, access for machinery and what lies underground already. A suburban garden may suit boreholes where trenches would not fit, while a rural plot with open ground may suit trenches at lower drilling cost.

A ground survey matters before any price is treated as firm. Soil type, rock depth, groundwater and the thermal conductivity of the ground all affect how much pipe or borehole depth is needed. A loop that is too short will cool the ground over successive winters and lose performance, while an oversized loop adds cost without a matching benefit. Installers therefore size the ground array from the home heat load and the ground properties together, not from a rule of thumb.

Inside the home, the system resembles other heat pump installations: a heat pump unit, often a cylinder, distribution pipework and controls. The difference is mostly outside, where trenches or boreholes, headers and the route into the building must be planned and then restored.

Check land ownership and boundaries, the position of drains, water pipes, cables and septic systems, and whether drilling rigs can reach the site without damaging drives, walls or trees. Ask whether a geological survey or trial borehole is recommended, what depth and spacing are proposed, and how the ground surface will be restored afterwards.

Also ask about permissions for boreholes, including water and environmental consents where they apply, and about the long-term effect of the array on future building, planting or drainage work on that land. Keep a drawing of the buried array, since future digging depends on it.

In the EU, borehole drilling and groundwater protection are regulated nationally and sometimes regionally, so consent, depth limits and reporting duties differ sharply between member states and even between regions. Some areas restrict drilling near aquifers or in protected zones, and those limits can decide between trenches and boreholes.

In the UK, boreholes may need environmental permits or abstraction considerations depending on depth and location, and MCS standards apply to certified installations. Planning and building control requirements, plus any conservation or protected landscape rules, should be checked for the specific site.

A costly mistake is agreeing a price before ground conditions are known, then facing extra charges when rock is harder or deeper than assumed. Another is planting deep-rooted trees over a shallow trench array, or later building an extension over a borehole field without knowing it is there.

A third mistake is undersizing the ground loop to save money, which may only show up after several winters as falling performance. Insist on a written array design with the assumptions behind it, and keep that design with the home records. One detail that is easy to overlook is the future use of the land above the array, since a later driveway, extension footing or deep-rooted hedge can conflict with shallow trenches or borehole heads, so marking the array on the property plan and telling any future contractor about it protects both the system and the next building project on that plot.

Keep the ground survey or borehole logs, the array drawing with depths and positions, the heat load calculation, the product data and the commissioning record, including the fluid type and fill pressure. Those records protect the next owner and any future tradesperson who digs on the land.

Ask a qualified installer: how was the ground array sized for this soil and this heat load, what consents are needed here, how will the surface be restored, and what happens if a loop later needs repair. Site-specific answers matter more than a generic efficiency claim.