Ground source heat pump boreholes and the consents

Planning permission is usually the easiest consent a ground source heat pump needs. Class G of Part 14 of Schedule 2 to the General Permitted Development Order 2015 permits the installation of a ground source heat pump within the curtilage of a dwellinghouse or a block of flats, with none of the conservation area restrictions that apply to air source units. The harder consents are the ones outside the planning system: an abstraction licence, an environmental permit, a borehole notification, and in coalfield areas a separate permit before anyone starts drilling.

Which of those apply turns on one design decision taken at the start. A closed loop system circulates fluid through sealed pipework and takes nothing out of the ground. An open loop system abstracts groundwater, passes it through a heat exchanger and returns it. The regulatory consequences are very different.

Closed loop and open loop

A closed loop array is sealed. Fluid, usually water with antifreeze, runs through continuous pipework in vertical boreholes or in horizontal trenches, and the only exchange with the ground is heat. Because nothing is abstracted or discharged, the abstraction and permitting regime does not engage.

An open loop system draws groundwater from an abstraction borehole and returns it, usually to a second borehole in the same aquifer. It is more efficient where the hydrogeology suits, and it brings the installation squarely within water law.

For most single dwellings the answer is a closed loop, because the volumes involved in an open loop are hard to justify against the licensing effort. Open loop becomes worth considering on larger buildings, on sites with a productive aquifer, and where cooling as well as heating is needed.

Which consents each route triggers

Abstraction of more than twenty cubic metres of water a day generally requires a licence from the Environment Agency under the Water Resources Act 1991, and an open loop system of any meaningful size will exceed that. Returning the water to the ground is a separate matter, requiring a permit for a groundwater activity under the environmental permitting regime, and the two are normally applied for together.

Allow real time for this. An abstraction licence application needs hydrogeological information about the aquifer, the proposed abstraction and return rates, the thermal effect on groundwater temperature, and an assessment of the effect on other abstractors and on any dependent wetland. On a contested aquifer the process is measured in months rather than weeks, and it can end in refusal.

Closed loop systems need neither, which is the main reason they dominate the domestic market. They are not entirely unregulated, because the Environment Agency has published its position on where closed loop systems are acceptable and expects them to be designed and installed so that the loop fluid cannot leak into groundwater.

Groundwater protection and source protection zones

Source protection zones are drawn around public water supply abstraction points, with the innermost zone representing the shortest travel time to the source. Drilling and installing a ground loop in the innermost zone is treated with considerable caution, and in practice is often ruled out.

Check the position before designing. The zones are mapped and publicly available, and so is the aquifer designation beneath the site. Three things to establish at the same time: whether the site sits in a source protection zone and which one, whether the underlying strata are a principal aquifer, and whether there is a known contamination plume nearby that a borehole could provide a pathway into.

That last point is the one most often missed on brownfield sites. A borehole through a contaminated made ground layer into a clean aquifer creates a vertical pathway, and the design response is a sealed casing through the contaminated zone with a grout seal, specified and verified rather than assumed.

Sensitive designations add their own layer. Operations on land within a site of special scientific interest need Natural England's consent separately from anything else, and a protected species or habitat on the drilling area or the access route needs resolving before plant arrives.

Notifying a borehole

Anyone sinking a borehole beyond the statutory depth threshold has a duty to notify the national geological records body and to supply the records of what was found, including the log of strata and water levels. The threshold is set in the Water Resources Act 1991 and the obligation is easy to discharge, but it is frequently overlooked by installers working on small domestic jobs.

Two practical reasons to care beyond compliance. The borehole log is the only record of the ground conditions under the site, and it is useful later for foundations, drainage and any contaminated land question. And a documented notification is what demonstrates the installation was carried out properly if the property is sold and a purchaser's surveyor asks.

In coalfield areas a further permit is needed before drilling that could intersect coal seams or former workings, and that is a separate process with its own lead time. The coalfield referral areas are mapped, and the check takes minutes.

Land take for a horizontal array

Where a site has enough land, a horizontal array avoids boreholes altogether and avoids most of the consent questions with them. The cost is land.

A horizontal collector needs a trenched or slinky arrangement over an area substantially larger than the footprint being heated, at a depth below the zone of seasonal temperature variation. That ground cannot subsequently be built on, cannot be planted with trees, and should not carry anything that would compact it heavily.

Three conflicts to resolve on the site layout before committing. Future extensions and outbuildings, because an array under the obvious place for a garage is an expensive mistake. Tree planting required by a landscape condition or a biodiversity commitment, since root protection areas and ground loops compete for the same volume. And drainage, because a soakaway or an attenuation feature over the array changes its thermal performance.

Mark the array on the site plan submitted with any application, even where the heat pump itself is permitted development, so that it appears in the planning record and is not later built over by a subsequent owner.

Noise and the plant room

The heat pump unit in a ground source installation sits indoors, which removes the external noise question that dominates air source installations. What remains is internal: the compressor and circulation pumps in a plant room adjoining a habitable space, and in a terraced or semi-detached property the party wall transmission.

Specify the plant room with that in mind, with resilient mountings, a lined enclosure where it adjoins a bedroom, and pipework isolated from the structure. This is not a planning matter in most cases, and it is the complaint most commonly made by occupiers after installation.

Farm and rural sites raise different questions again, where the generation and heat strategy interacts with the permitted development limits covered in our note on farm wind turbines and permitted development limits.

Coordinating with the energy statement

Where an Energy Statement is required, the ground source system needs to appear in it with a stated seasonal performance figure, the basis for that figure, and the carbon saving calculated against a named and dated grid emissions factor. A system claimed at a performance level the ground conditions will not support is the thing a reviewer tests.

Align the statement with the Sustainability Statement if both are being submitted, and make sure the ground loop arrangement described in each is the same one. Our companion note on ground source heat pumps and borehole permitting goes further into the permitting sequence itself.

This is general guidance, not legal advice; check the position with your local planning authority or a qualified professional before relying on it. A Lawful Development Certificate is the only formal way to confirm that works are lawful without planning permission. PlanScope drafts energy and sustainability statements structured to UK planning policy, with gaps flagged where site data is still needed. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.