When people talk about decarbonising heat in the UK, the conversation usually goes to heat pumps. They’re proven, they’re scalable, the grants are available, and the industry has grown up around installing them in British homes. But there’s another heat source that doesn’t require you to install anything in your property at all — one that’s been sitting under the ground the whole time.
Deep geothermal energy is having a quiet moment in the UK. Projects that spent years in the permitting and funding phase are now drilling, and early results are more promising than the historically sceptical British energy establishment expected.
What Deep Geothermal Actually Is
The Earth’s core is hot. At depth, even in geologically quiet areas like the UK, rock temperatures rise — roughly 25-30°C per kilometre in average UK geology, with granite formations in Cornwall and Devon running hotter, up to 40°C per kilometre in places. Deep geothermal projects drill down several kilometres, circulate water through the hot rock, and bring heat back to the surface.
This is different from ground-source heat pumps, which only go a few metres down and harvest the shallow, solar-heated ground layer. True deep geothermal taps the planet’s internal heat and doesn’t depend on surface temperature at all. You could drill in January, at midnight, in the middle of a cold snap, and the heat output would be exactly the same.
The catch is the drilling cost. Going three to five kilometres into hard granite costs tens of millions of pounds per well. That’s not something you put in someone’s garden — it’s infrastructure that serves a community, a district heating network, or an industrial process.
What’s Actually Happening in the UK
The United Downs Deep Geothermal Power project in Cornwall is the furthest advanced. It’s drilled two wells to depths of around 5,200 metres and 2,400 metres into the Cornish granite batholith, which runs at temperatures above 180°C at depth. The project has been operating in the heat production phase and is evaluating electricity generation from the residual steam. United Downs isn’t large — it’s demonstration-scale — but it’s established that UK deep geothermal works in practice.
More interesting for heating applications is the Eden Geothermal project, also in Cornwall, which aims to deliver heat and power to the Eden Project site. It’s drilling to around 4.5 kilometres into the same granite formation and has the advantage of a ready heat customer in the Eden Project’s tropical biomes, which require year-round heating.
The UK Geothermal Association estimates there are around twenty active or near-active geothermal development projects across the UK in various stages of development. The geology favourable to deep geothermal extends well beyond Cornwall — the Lake District, north-east England, and parts of Scotland all have potential.
The District Heating Angle
Here’s why this matters for how heat gets delivered to UK homes. Deep geothermal at this scale isn’t about individual properties — it’s about anchor heat supply for district heating networks. A hot water loop supplied by a geothermal well could heat hundreds or thousands of homes in a defined geography.
The UK has been rebuilding interest in district heating networks as part of heat decarbonisation strategy. The Heat Network Zoning consultation, which DESNZ has been running, is designed to designate areas where district networks are the most cost-effective heat decarbonisation route. If a geothermal resource is available within a heat zone, it becomes a genuinely competitive option — zero-carbon heat that doesn’t require individual households to do anything except connect to the pipe in the street.
The economics look better when you frame it this way. The drilling cost is high, but the marginal cost of heat once the wells are drilled is very low. No fuel cost, no fuel price risk, very low operating cost. A geothermal anchor can supply a district network for decades.
Why It’s Not Everywhere Yet
A few things are slowing deployment. First, the geology isn’t uniform — not every area of the UK has the hot granite formations that make deep geothermal viable. Second, the permitting process for deep drilling in the UK is complex, involving both subsurface access rights and environmental assessment. Third, there’s limited domestic experience with deep geothermal development, which adds cost and uncertainty to each project.
The financing model is also unusual. Geothermal projects have high upfront capital costs and long operating lives — more like infrastructure than energy generation. The UK government has so far provided some grant funding through Innovate UK and UKRI for exploratory projects, but there’s no equivalent of the Contracts for Difference support mechanism that enabled offshore wind to scale.
That may change. The Climate Change Committee has noted geothermal as an underexplored option in UK heat strategy, and there’s cross-party interest in establishing a more structured financing pathway.
What It Means for Homeowners Right Now
Honestly, not much immediately. If you need to heat your home in 2026, geothermal district heating isn’t going to be available in your area unless you’re in a very specific part of Cornwall or a handful of other early-stage network areas.
What it does mean is that the UK’s heat decarbonisation options are more varied than the heat-pump-or-nothing framing suggests. If you live in an area designated as a heat network zone in the next few years, there’s a realistic chance the anchor supply for that network could eventually be geothermal — which would mean cheap, stable, low-carbon heat without any equipment in your home.
For the medium term, heat pumps remain the most accessible route to low-carbon heating for individual properties. But geothermal is building a case, well by well, that it belongs in the UK’s heating mix for the 2030s.