As the NHS accelerates its journey towards Net Zero, low-carbon heat technologies are no longer theoretical. Heat pumps, geothermal systems, and low-carbon energy centres now feature regularly in board papers, capital plans, and strategic discussions. Yet those involved in delivering these schemes are increasingly clear about one thing: the success or failure of low-carbon heat rarely hinges on the technology itself.
Instead, it is the condition — and readiness — of the existing estate that determines whether projects succeed, stall, or quietly unravel once the operational realities of live hospitals come into play.
“People tend to focus on the technology,” says Andy Yates, “but the reality is that low-carbon heat will only ever perform as well as the system you’re connecting it to.”
The temperature problem no one can ignore
At the heart of most low-carbon heat discussions sits a deceptively simple issue: temperature.
“Whatever technology you’re talking about, lower temperatures make everything easier,” Rob Hilliard explains. “They improve efficiency, reduce energy input, reduce stress on equipment, and give you much more operational flexibility.”
Low-carbon heat sources are fundamentally different from traditional gas boilers. They perform best when supplying heat steadily at lower temperatures, rather than responding to short bursts of high demand. The difficulty is that much of the NHS estate was never designed with this operating philosophy in mind.
Many hospitals still rely on high-temperature LTHW systems — or, in some cases, legacy steam — with flow temperatures of 80—90°C. Those temperatures were historically used to compensate for oversized systems, long distribution runs, and poor insulation, rather than because clinical spaces genuinely required them.
“These systems evolved in a very different energy world,” Yates notes. “Cheap gas, high temperatures, constant flow. They worked — but they’re fundamentally misaligned with where we need to go.”
Trying to introduce low-carbon heat without addressing this mismatch often results in complex hybrid systems, higher capital costs, and disappointing operational performance.
Discovering headroom in existing systems
Despite this, both are keen to stress that NHS estates are often more adaptable than expected.
“We regularly find systems that are massively oversized for today’s loads,” Hilliard says. “Radiators, coils, pipework — there’s often far more capacity there than people realise.”
In many cases, hospitals were designed for worst-case winter scenarios that no longer reflect modern building fabric, internal heat gains, warmer winters, or clinical usage. As a result, systems that appear locked into high-temperature operation may in fact have significant untapped headroom.
Simple, carefully managed testing — progressively lowering flow temperatures and monitoring comfort, response times, and complaints — can provide invaluable insight. This approach allows estates teams to understand real-world performance rather than relying solely on historical assumptions or design intent.
“We’ve seen sites operate comfortably at 55°C all winter with no complaints at all,” Yates adds. “No new plant. No emitter upgrades. Just turning it down and seeing what happens.”
That evidence does more than save energy. It builds confidence across estates, clinical teams, and senior management that change is possible without compromising patient care.
The unfashionable work that makes projects viable
Much of the most important preparatory work is not particularly eye-catching. Replacing constant-speed pumps with variable-speed drives. Removing three-port valves that short-circuit systems. Improving BEMS optimisation, zoning, and temperature compensation. Fixing insulation and reducing distribution losses.
“These aren’t the things that get headlines,” Hilliard admits, “but they’re the things that make low-carbon systems affordable to run and manageable day to day.”
Poor control and inefficient hydraulics can undermine even the best-designed low-carbon heat source. Without addressing these fundamentals, trusts risk transferring inefficiency from one energy source to another.
Yates is clear on the financial implications. “If you try to bolt low-carbon heat onto an inefficient estate, you can end up with eye-watering revenue costs. Capital might be grant-funded, but operating costs still land with the trust — and that’s where projects quickly become unpopular.”
Many of these interventions are self-funding, delivering immediate operational savings while quietly creating the conditions needed for future decarbonisation.
Where backlog and Net Zero meet
One of the strongest themes to emerge from the discussion is the opportunity to align decarbonisation with the NHS’s critical estates backlog.
“Plant replacement is happening anyway,” Yates says. “Boilers, pumps, controls — a lot of this kit is life-expired. The question is whether you replace like-for-like, or whether you use that moment to future-proof the estate.”
Too often, backlog replacement and decarbonisation are treated as separate — or even competing — priorities. Yet in practice, they are closely linked.
Hilliard sees the consequences when that alignment is missed. “We sometimes arrive at sites where trusts want low-carbon heat, but the surrounding infrastructure is fundamentally unfit for purpose. You’re not removing risk — you’re just moving it.”
When planned together, backlog replacement becomes an enabler rather than a constraint. Life-expired pumps can be replaced with variable-speed systems sized for lower temperatures. Obsolete controls can be upgraded to allow zoning and sequencing. Distribution upgrades can reduce losses and unlock lower flow temperatures.
“It’s often about spending the same money more intelligently,” Yates reflects. “And avoiding spending it twice.”
This alignment also reduces operational risk — a critical consideration for estates teams already managing fragile infrastructure under intense pressure.
Strategy over short-term fixes
Both Yates and Hilliard are clear that technology-led projects without a long-term strategy are vulnerable.
Hospitals are dynamic environments. New clinical buildings come on line, older buildings are repurposed or demolished, and service models evolve. Without a clear long-term heat strategy, decarbonisation risks becoming reactive — responding to funding opportunities rather than following a coherent plan.
“You need to understand the end state,” Hilliard says. “What does heat distribution look like in 2035 or 2040? Which buildings are long-term assets? Which systems should be adapted, and which should be retired?”
Without that clarity, there is a real risk of investing in solutions that limit future options or lock in inefficiencies for decades.
The role of data
Data — or the lack of it — remains a persistent frustration.
“Poor data is where projects come unstuck,” Hilliard notes. “If you don’t really know your loads, flows and returns, you’re designing blind.”
Reliable metering, monitoring, and asset data underpin good engineering decisions. They reduce contingency, improve sizing accuracy and build confidence in both capital and operational performance.
Investing in data early often pays for itself many times over by avoiding over-engineering and unnecessary complexity.
A practical way forward
For trusts wrestling with how to start, the message is deliberately pragmatic.
“This isn’t about ripping everything out tomorrow,” Yates says. “It’s about preparing the ground.”
That preparation might include:
- testing and reducing flow temperatures where possible
- targeting low-cost efficiency measures that improve control and reduce demand
- aligning decarbonisation plans with critical backlog replacement
- investing in data and metering to inform future decisions
- developing a clear long-term heat strategy that reflects how the estate will evolve.
When approached this way, decarbonisation stops being an added burden and becomes a route to a more resilient, affordable and future-ready estate.
“The question now isn’t whether low-carbon heat can work,” Yates concludes. “It’s whether we’re setting our estates up to let it succeed.”
Steve Heape
Steve Heape is chair of the IHEEM Environment and Sustainability Advisory Platform and a leading figure in the UK’s healthcare decarbonisation landscape. He has spent over a decade developing and delivering large scale low-carbon energy infrastructure across NHS estates, including heat pumps, geothermal, solar PV, CHP and energy performance contracts. Steve is deeply involved in innovation around Net Zero hospitals, district energy, and new clean-energy business models, and is passionate about turning complex energy challenges into deliverable, investable solutions.
Andy Yates
Andy Yates is a Chartered Mechanical Engineer and head of projects at the Carbon and Energy Fund, leading the development and delivery of complex NHS decarbonisation programmes. He specialises in large-scale energy infrastructure, procurement, and Net Zero strategy, with a strong track record over the last 32 years of delivering multi-million pound heat, power, and efficiency projects across public sector estates.
Rob Hilliard
Robert Hilliard is a senior development engineering manager at Vital Energi Utilities Limited, specialising in low-carbon energy solutions. He has extensive experience in designing and delivering complex heat and power infrastructure projects, supporting public and private sector clients in their transition to Net Zero.