Ground Source Heat Pump Installers: What to Ask Before You Tender

Of all the technologies, ground source is the one where the choice of installer matters most, because so much of the value and risk sits underground where nothing can be inspected after the fact. The array has to be designed from real ground data, the drilling has to be done properly, and the system has to be balanced so the ground does not gradually cool over years of operation. This guide sets out what to ask ground source heat pump installers before tender, how to read the answers and where the money goes.

Where ground source earns its premium

Ground source draws on the stable temperature of the ground through boreholes or horizontal loops, and because that source barely changes through the seasons the efficiency holds up on the coldest day of the year, when air source dips. Typical commercial ground source projects run at an SCOP often above 4.0 across the year, with the bonus of low-cost cooling in summer. It earns that premium on buildings occupied and heated every day of the year, such as care homes, hospitals, hotels and leisure centres, and is often a poorer fit for a seasonally occupied building.

Question 1: will there be a ground investigation and thermal response test?

Sizing a borehole array from a textbook assumption of ground conductivity is the most common way to get a ground source system wrong. A ground investigation and a thermal response test before final design match the array to the actual thermal conductivity of your ground. If an installer prices an array without either, ask what ground data the price assumes and who carries the cost if the ground turns out to be different.

Question 2: how is the array kept in thermal balance?

If a building only ever extracts heat from the ground in winter and never returns any in summer, the ground around the boreholes can cool slowly over the years and the efficiency drifts downward. On a building that also needs cooling, rejecting summer heat back into the array delivers that cooling cheaply and recharges the ground for the next heating season. Ask the installer to show how the array has been sized for both the heating extraction and any cooling rejection, and over what design life. The cheapest borehole quote is often the most expensive choice over twenty years: an under-sized array drilled to save a few boreholes will draw the ground down and erode the SCOP you were sold, and more boreholes cannot be drilled once the building is finished and the car park is back in place.

Question 3: boreholes or horizontal loops, and why?

The choice comes down to the land available. Boreholes, typically 100 to 200 m deep, need only a modest surface footprint and suit constrained urban sites, but the drilling is the larger cost. Horizontal loops are cheaper to install where there is open ground to trench, but they need a substantial area and are more affected by surface seasonal temperature than deep boreholes. The number and spacing of boreholes should follow from the thermal response test, not from a rule of thumb.

Question 4: who does the drilling, and who is responsible?

Drilling is frequently subcontracted. That is not a problem in itself, but it needs to be visible: ask who drills, what their competence and insurance are, who is responsible for the work if the array underperforms, and what testing and records are provided when the boreholes are complete. As with any installer, check the certifications you can check. The guide to checking MCS certification shows how to use the directory, and the heat pump itself needs F-Gas certified handling of refrigerant.

Question 5: what efficiency is promised, and to which standard?

Ask for a seasonal efficiency to BS EN 14825, with the design flow temperature stated, and for the model behind it. Every degree of flow temperature shed lifts the SCOP, so a ground source quote that keeps high-temperature radiators in place is giving away part of the advantage it is charging for. Rated COP to BS EN 14511 is a point-in-time figure and should not be compared with a seasonal one.

Question 6: how is the programme and the disruption handled?

Ground source takes longer to deliver than air source because of the ground works. Ask for a programme that shows the ground investigation, the thermal response test, the design freeze, the drilling window, the connection of the array to the plant room and commissioning as separate steps, and ask what happens to the existing boiler during the works. A sound plan keeps the existing heating live until the new system is commissioned, so the building is never without heat, and schedules the changeover around the operating calendar. Drilling brings noise, spoil and access questions on an occupied site, so ask where the rig will stand, how the spoil is handled and how the site will be reinstated.

Question 7: what is the plan for cooling and controls?

Where the building has a cooling load, the array can supply low-cost cooling by reversing the flow, and the same heat that is rejected in summer recharges the ground for the next winter. That only works if the design, the controls and the building services are aligned, so ask the installer to show how cooling is controlled, what it does to the array temperature over the year and who is responsible for the interface with the existing building management system. Weather compensation and buffer arrangements hold the flow temperature down in real operation instead of only on paper, and a system that is sized correctly but left at a fixed high flow temperature will not deliver its rated seasonal efficiency.

How to read the answers

Good answers are specific and refer to your building: the measured conductivity, the number of boreholes and their depth and spacing, the peak and annual loads, the heat rejected in summer, the design flow temperature and the seasonal efficiency that follows from it. Weak answers lean on generalities such as a typical borehole depth or a typical efficiency, or on a brand name. A firm that welcomes a second opinion on its model is usually a firm that expects it to stand up. A firm that resists sharing the model is telling you something about the model.

Funding and tax for ground source

The Boiler Upgrade Scheme (England and Wales) can be used for a building used for a business, not only a home: it pays £7,500 towards an air source or ground source heat pump that replaces a fossil-fuel heating system, within DESNZ capacity caps (45 kWth for a single system), and hybrid systems are excluded. For ground source, the scheme reaches single systems within the 45 kWth cap and a shared ground loop within 300 kWth, so larger commercial arrays rely on other routes. The Public Sector Decarbonisation Scheme has had no open application window since Phase 4 closed in November 2024, and gov.uk lists no further phase. The Green Heat Network Fund runs in application rounds: Round 12 closed on 25 September 2026, so check gov.uk for the next round. Tax relief works differently from what many guides say: a heat pump is part of a space or water heating system, which HMRC lists as an integral feature (special-rate plant), and full expensing covers main-rate plant only. The Annual Investment Allowance gives 100% relief up to its limit (£1 million), and companies can then claim a 50% first-year allowance on special-rate plant, with a 6% writing-down allowance on the rest. Confirm the treatment with an accountant. Current status for each route is on the grants and funding page.

A short tender checklist

• Ground investigation and thermal response test before final design.
• Array sized for heating extraction and any cooling rejection, with a stated design life.
• Borehole or loop choice justified by the land available.
• Named drilling contractor, with competence, insurance and responsibility set out.
• SCOP to BS EN 14825 at a stated flow temperature, with the model attached.
• DNO supply check and G99 work identified early, and a planning position on borehole arrays.
• An itemised price, a commissioning pack and a maintenance plan.

For the cost side, see the commercial heat pump cost guide, and for the broader process the guide to choosing a commercial heat pump installer. To test whether ground source suits a particular building, the brief request takes meter data and returns a plain assessment with no obligation.

What should I ask a ground source heat pump installer?

Ask about the ground investigation and thermal response test, how the array is kept in thermal balance, who does the drilling and who is responsible for it, and what seasonal efficiency is promised to BS EN 14825 at what flow temperature.

How much does a commercial ground source heat pump cost?

The figure depends on the heat load, the ground and the emitters.

Can a business get the Boiler Upgrade Scheme for a ground source heat pump?

Sometimes. The scheme can be used for a building used for a business in England and Wales, within DESNZ capacity caps of 45 kWth for a single system and 300 kWth for shared ground loops, replacing a fossil-fuel system. Larger arrays rely on other routes.

Why is thermal balance important for a borehole array?

If heat is only ever extracted, the ground around the boreholes can cool over the years and the efficiency drifts downward. Returning summer heat to the array, where the building has cooling demand, recharges the ground.