The Rule-of-Thumb Problem - and a new 5-point GSHP feasibility checklist to support your ground source projects

Ground source heat pumps (GSHPs) are among the most efficient, lowest-carbon ways to heat and cool buildings: cutting energy costs and improving resilience for decades. So why are potential projects being dismissed before a spade hits the ground?

Our experience (and the data we see across early-stage pipelines) says most “no” decisions don’t come from physics. They come from myths, generic assumptions, and weak early coordination. This piece shows where good projects go to die - and how to keep them alive long enough for the facts to win.

Let’s reap the rewards for developers, contractors, and the climate. 

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1) The “rule-of-thumb” trap

Early feasibility is often built on quick averages: “typical” borehole depths, standard loop lengths, assumed ground conditions. It’s fast, but it’s not your site.

What goes wrong:

• Drilling costs get inflated by worst-case geology estimates.
  
  
• Systems are over- or under-sized to chase a spreadsheet, not reality.
  
  
• Viable designs are ruled out before site-specific data exists.
  
  

What to do instead: move from heuristics to site-specific modelling early. That means ground investigation, credible load profiles, realistic drilling pricing, and thermal response inputs tied to your actual plot.

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2) Three persistent myths (and why they fall apart)

“GSHPs are too expensive.”
Total cost of ownership matters. Long lifespans for ground arrays and stable operating costs routinely beat short-cycle replacements and volatile fuels.

“They only work on big, open sites.”
Dense sites can be designed with shared plant and smart manifold design; constraints drive design choices, not automatic disqualification.

“You can’t retrofit them.”
Retrofit complexity is real, but so is success when design leads. Mixed-use and heritage-sensitive sites can accommodate GSHPs with the right architecture and phasing.

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Ultra-prime, conservation area, tough targets? Still a win…

At 52 Avenue Road (St John’s Wood) we designed a communal GSHP system with a central plant room feeding individual water-to-water units per dwelling. Result: 74.3% on-site carbon reduction: more than double the policy requirement. Design was re-validated through regulatory changes and drilling challenges, with varied borehole depths and live redesigns to maintain COP and compliance.

District style retrofit momentum

At Sydney Street (Chelsea), feasibility for a local GSHP network scoped around 174 boreholes, delivering 1,743 kW peak heat, and service to approximately 75% of local buildings: the kind of area-level deployment that makes retrofit practical at scale.

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3) Where coordination breaks (RIBA 1–3)

Most risk enters, and value leaks, before technical design:

• Vague M&E briefs and unclear performance targets
  
  
• No early geotechnical insight, so risk allowances balloon
  
  
• Siloed decision-making, so feasible options never get a fair run
  
  

Fix the sequence, fix the outcome: pair concept design with GSHP specialist input early, define performance/comfort set-points up front, and commission targeted ground data before locking in costs or dismissing options. For more on de-risking GSHP projects, explore our full article on the subject. 

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4) The cost of walking away too soon

Ruling out GSHPs prematurely often locks projects into:

• Higher lifetime energy spend
  
  
• Higher operational carbon for decades
  
  
• Exposure to fuel-price volatility
  
  
• Lower resilience against comfort and grid constraints
  
  

In a world of rising standards (FHS, MEES, and local planning policies), the wrong source of heating and cooling for a project becomes a strategic liability. Unpack what new standards in new-build construction mean for your next project in more detail here. 

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5) What does“proper GSHP feasibility” actually look like? (checklist)

A credible early pass typically includes:

Demand & comfort

• Robust heat/cool load profiles (by use & zone), not flat “typicals”
  
  
• Set-points, DHW duty, diversity, and shoulder-season logic
  
  

Ground & drilling

• Desk geology + targeted ground investigation plan
  
  
• Thermal response factors aligned to likely drilling strategy
  
  
• Realistic drilling access, reinstatement, and sequencing
  
  

System concept

• Closed/open loop selection rationale
  
  
• Central plant vs. distributed water-to-water reasoning
  
  
• Controls philosophy, hydraulic separation, temperatures (e.g., around 20 °C LT loop with 45–65 °C dwelling lift where appropriate)
  
  

Commercial & risk

• CAPEX with transparent drill/plant allowances
  
  
• OPEX with tariff scenarios and sensitivity
  
  
• Regulatory pathway (planning, conservation, utilities)
  
  
• Risk register with designable mitigations
  
  

Decision clarity

• Go/No-Go based on whole-life view, not just upfront spend

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From policy to proof

Policy direction is clear: higher standards and lower emissions are non-negotiable. The right way to respond isn’t to squeeze through loopholes; it’s to deploy systems that already clear the bar and keep clearing it as standards tighten.

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Our stance (and why it matters)

We’re a design-only GSHP consultancy. No hardware to sell. No installation quotas. Just 20+ years of ground source thinking focused on feasibility, modelling, and delivery support

Ready to stop good projects being ruled out for the wrong reasons?

• Ask for a second opinion: If GSHP has been ruled out at RIBA 1–3, send us the brief and the feasibility: we’ll stress-test the assumptions.
  
  
• See the work: Explore case studies and what proper GSHP feasibility looks like in practice.
  
  
• Talk to an engineer: whitecoat@geniusenergylab.com

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