27 May 2025
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Chris Davidson, CTO at Genius Energy Lab, offers an insightful perspective on embodied carbon, which he believes should be considered alongside operational carbon to form a complete lifetime carbon profile for systems expected to operate for up to 100 years.
As pressure mounts to decarbonise the UK’s building stock, heat pump systems are stepping into the spotlight. The shift away from gas is well underway, and last year the UK’s greenhouse gas emissions dropped to their lowest level since 1872 - largely thanks to phasing out coal-fired power and scaling up renewables. We’ve made real gains by cleaning up electricity - the more straightforward part of the decarbonisation puzzle. But when it comes to heating and cooling, progress has barely begun, and with performance metrics still geared towards short-term figures, there’s a real risk they’ll skew long-term decisions in ways that aren’t immediately obvious.
Much of the current conversation around carbon focuses on what happens before the system is even switched on - what’s known as embodied carbon. It’s now a common feature in client briefs and public sector frameworks, and rightly so. We should certainly account for the carbon cost of manufacturing, transport, and installation of a system, but too often, assessments stop there. What’s often overlooked is how that system performs over the long haul. In reality, the bulk of a heating or cooling system’s carbon footprint doesn’t come from its manufacture - it comes from how efficiently it runs over time, and how long it lasts. Embodied carbon needs to be taken into consideration alongside operational carbon to create an overall lifetime carbon picture for systems operating for 50, 75 or even 100 years.
Focusing too heavily on embodied carbon risks creating a false economy. On paper, a ground source system may seem like the higher-carbon choice at installation, but over time, the numbers tell a different story. To get a more accurate measure of environmental impact, we need to bring a broader lens to the assessment. That means going beyond emissions from manufacture and delivery, and accounting for actual energy use, replacements, and how well the system performs in use. It means thinking in terms of lifetime carbon. Whole-life carbon assessments are already making their way into public sector projects - and they’re only going to grow in importance. For anyone working in design or installation, it’s worth getting ahead of that shift now.
When comparing heating and cooling systems over their full lifespan, the numbers tell a very different story. Take a 1MW installation: whether you opt for a closed-loop ground source heat pump, an air source heat pump, or a gas boiler paired with a VRF or VRV system, the picture changes once performance over time is factored in. On first glance, embodied carbon, the emissions from manufacturing and installation, doesn’t favour the GSHP. But that’s only part of the equation.
A closed-loop GSHP, evaluated over a 100-year period to reflect the longevity of the borehole, generates around 34% of the lifetime carbon emissions of a typical gas boiler and VRF system. An equivalent ASHP system comes in at around 48% - and in both cases, that gap is likely to widen. As the UK grid continues to decarbonise, the operational emissions of electrically driven systems like GSHPs and ASHPs will fall further, making the long-term carbon case even stronger.
The difference lies almost entirely in how each system uses energy. Ground source systems operate at higher efficiencies, typically delivering a coefficient of performance (COP) of around 4 for heating and a seasonal coefficient of performance (SCOP) of 5 or more for cooling, thanks to the stable ground temperature acting as a natural heat sink. That efficiency extends to design simplicity too: no need for extra rooftop plants, ducting, or cooling equipment. Air source systems, by contrast, are more exposed to ambient temperature swings and usually achieve a COP and SCOP closer to 3, with more variability. Gas systems, of course, carry the ongoing carbon penalty of burning fossil fuels - and when paired with electric cooling, their operational emissions rise even further.
While ground source systems carry more embodied carbon up front - largely due to borehole drilling and material - this so-called “carbon debt” is paid back surprisingly quickly. In fact, the GSHP catches up with ASHP on total emissions in just over a year. After that, every kilowatt hour saved is a long-term gain, so although embodied carbon might be the easiest thing to count, it’s the least important number in the long run. For systems that will be running for generations, what really matters is how efficiently they operate and how long they last without major reinvestment. That’s especially true of ground source systems, where the underground loop can last 50 to 100+ years - far outliving most components in ASHPs or conventional systems. Fewer replacements means lower embodied carbon over time, and a more stable system with fewer disruptions. Conventional systems don’t fare any better. A gas boiler might be fine for heating, but cooling still requires a separate system which carries its own embodied carbon, replacement cycle, and operational inefficiencies. Put simply: GSHPs are pulling double duty. They offer an efficient, low-carbon, integrated system with fewer replacements, lower emissions, better long-term performance, yet they’re often overlooked, not because they underperform, but because their value is masked by a slightly higher upfront cost. That puts GSHPs at an unfair disadvantage, even when they deliver far better long-term outcomes.
A call to action: Think long-term
It’s tempting to focus on embodied carbon - it fits neatly into procurement metrics. But that short-term view tells only part of the story. A system that looks low-carbon on day one might tick a box in a spec sheet, but it won’t stand up to scrutiny if you’re serious about climate impact. So what does this mean for those specifying, designing, and installing these systems?
For installers, it’s about being prepared to challenge assumptions. If a client or contractor pushes back on GSHPs due to embodied carbon, it’s worth asking what timeframe they’re measuring over. If the goal is to decarbonise the building’s energy use for the long haul, a system that repays its carbon debt in a year and performs for decades is the smarter investment.
For consultants, this shift demands a more joined-up approach to lifecycle thinking. Whole-life carbon assessments aren’t just for flagship net-zero schemes anymore, they’re becoming part of standard sustainability metrics, especially in the public sector. Factoring in replacement cycles, efficiency in cooling, and operational variability should be core to the design process, not bolted on afterwards. And for manufacturers and suppliers, there’s an opportunity to take the lead in how carbon data is presented. It’s one thing to provide an embodied carbon figure for a unit, but it’s far more useful to supply lifecycle data that reflects how that system performs in context.
We all know that heating and cooling systems don’t exist in a vacuum. They’re part of complex buildings, often serving multiple needs, over long lifespans. That means the way we talk about carbon impact needs to evolve, because the tools and language we’re using now aren’t giving clients, or contractors, the full picture. If we’re serious about net zero, we need to stop treating embodied carbon as the f inal word. It’s one metric — not the whole picture. What matters is what happens in year ten, thirty, or seventy-five. That’s why lifetime carbon should be the baseline for every serious heating and cooling spec.
Ground source systems are infrastructure, not just equipment. When properly planned and installed, they can deliver efficient, low-carbon heating and cooling for generations. For those in the trade - whether you’re specifying, designing, or on the tools - the shift to lifetime carbon thinking is a chance to lead, challenge short-termism, and make decisions that stand the test of time. Because if we’re going to decarbonise heat properly, we need to look past what’s easiest to quantify today, and start thinking about what we’ll be living with tomorrow.
