Upgrading Britain’s 29 million homes to low-carbon heating by 2050 is one of the country’s biggest decarbonisation challenges.
Heat networks and their role in decarbonising UK’s residential heat
Heat networks are systems that distribute heat from a central source to multiple dwellings. They could be communal (serving one building) or district (serving multiple buildings) and can leverage economies of scale and flexible heat sources to cut carbon and improve efficiency. Heat networks are seen as a key solution to decarbonise residential heat at scale.
Instead of fitting individual gas boilers in every flat, heat networks enable centralised heatgeneration from a single energy centre, distributing heating and hot water through insulated pipes to multiple dwellings. This centralisation means that simply swapping the heat source, for instance, replacing a gas boiler plant with a large heat pump or other renewable source can decarbonise hundreds of homes at once.
This flexibility, combined with economies of scale and the ability to use diverse energy sources (such as industrial waste heat or geothermal), makes heat networks a key pillar in the UK’s strategy to decarbonise building heat. The government hopes to expand heat networks to supply at least 20% of UK building heat demand by 2050, all from low-carbon sources in order to reach net zero – a huge increase from today’s 3%.
Achieving this will require not just more heat networks, but better heat networks that deliver low-carbon heat efficiently and affordably.
Why heat networks make sense in social housing?
According to National Housing Federation, there are over 14,000 heat networks across the UK (about 90% in England), supplying heat and hot water to about 500,000 households, which make up around 3% of national heat demand. And the majority (about 66%) of existing heat networks are operated by social housing providers – with around 150,000 housing association homes connected. In fact, an estimated 1 in 12 social housing households are on heat networks (versus about 1 in 25 households overall) – underscoring the critical role of heat networks in decarbonising social housing sector at scale.
In high-density, ‘retrofit-prone’ social housing scenario, heat networks offer a compelling decarbonisation pathway, but only if designed and operated correctly.
Learning from past mistakes: the challenges associated with older heat networks
The early era of heat networks in social housing (dating back to 1960s-70s high-rise flats) suffered from systemic issues such as
1. High distribution losses: Performance data shared by Heat Trust reveals that most existing UK heat networks operate at only about 35-45% efficiency, meaning a staggering 55-65% of generated heat is lost before reaching consumers – lost in pipes and plant rooms due to oversized designs, high flow temperatures and inadequate insulation. Many legacy heat networks were designed like standard boiler systems on a larger scale – often oversized (with generous margin upon margin for peak demand) and running at unnecessarily high temperatures. Oversizing and high fixed temperatures mean that during most of the year, pipes were carrying more hot water than needed, and much of that heat bled away into communal areas. This not only wasted energy but also caused overheating in communally heated buildings.These losses due to wasted energy translated into higher costs and poorer outcomes for residents. Lost heat means more fuel must be burned to meet demand, driving up consumer bills (especially since most networks still use gas bought at uncapped commercial rates).
2.Domestic hot water (DHW) storage inefficiencies
Older communal heat network systems often used large hot water storage cylinders in each dwelling or central tanks with recirculation loops. While common, this reintroduced inefficiencies associated with older systems, such as constant heat losses from standing water and pipework, and the need to run networks at >60C to prevent Legionella.
This design often leads to high return temperatures, eroding system performance. As the DESNZ research shows, such systems can lose more than half the energy they generate.
3. Impact on tenants: real-world consequences
These inefficiencies don’t just hurt carbon targets, they impact people’s lives as well. A 2021 investigation by Inside Housing uncovered several examples where tenants suffered from heating and hot water system breakdown, coupled with rising costs.
One Barking Riverside resident went seven weeks without hot water. Some residents paid over £5000 for heating over four years, almost double the typical UK gas bill. Complaints went unanswered for weeks, with residents unable to switch providers or seek redress due to the monopoly nature of many schemes.
This has led to growing pressure on housing associations and local authorities to improve system reliability, transparency and affordability.
A changing regulatory landscape
To address these concerns, Ofgem has now been appointed as the statutory regulator for heat networks in the UK, marking a major shift towards mandatory consumer protections, fairer pricing and enforceable standards.
From 2025, all heat network developers will need to register their networks, comply with technical and performance standards, and ensure customer rights and compensation mechanisms are in place. This regulatory change is critical for restoring tenant trust and delivering the promise of heat networks.
So what should specifiers do differently?
And how Sunamp Thermino makes a difference
To avoid repeating the inefficiencies of legacy heat networks and ensure that new schemes truly deliver on carbon savings, affordability and tenant comfort, specifiers must rethink their approach from the ground up.
As the Heat Trust data has shown, many existing networks operate at just 35–45% efficiency, with more than half of generated heat lost in distribution due to oversized pipework, excessive operating temperatures, poor insulation and always-on circulation loops.
New networks must be designed to minimise these losses, through right sizing, careful and intelligent zoning, better insulation – complying with design methodologies outlined within CIBSE CP1 Heat networks: Code of Practice for the UK (2020) (maximum acceptable communal distribution system heat loss =100W/dwelling).
In essence, domestic hot water recirculation loops are used to ensure instant hot water at every tap, especially in multi-dwelling buildings. These loops keep hot water constantly flowing through pipework and back to the central plant to avoid delays and temperature drops. However, they require constant pumping, which consumes electricity/energy usage. The pipework continuously loses heat to the surroundings, especially if insulation is poor. With the introduction of the Heat Network Technical Assurance Scheme (HNTAS) in 2025, all heat network operators must now show compliance with mandatory minimum technical standards and key performance indicators, which include efficient water flow temperatures and pipe insulation.
Thermino heat batteries tackle the challenge of ‘always-on recirculation loops’ found in traditional systems by storing heat locally in each dwelling as latent energy in its Plentigrade phase change material (PCM), releasing it only when needed.
This setup means no need for central hot water storage or long hot water pipe runs, and with no recirculating loop, there is no pipework constantly losing heat into communal areas or risers. This can reduce distribution heat losses, particularly in large or high-rise buildings. Thermino can also be charged daily or based on off-peak tariff/PV availability, rather than being kept ‘hot and ready’ like hot water cylinders and loops.
In addition, Thermino heat batteries are legionella-safe by design. Because no standing water is stored in the hot water circuit and as the volume of water in the system is very low (<15L), Legionella risk is inherently mitigated.
Thermino heat batteries can heat mains pressure fresh cold water on demand, so water doesn’t stagnate, and there is no need of the energy-intensive legionella protection cycles, unlike a traditional hot water cylinder. This means less maintenance hassle for landlords.
This not only enhances efficiency but also cuts the overall heating system design complexity, maintenance costs and compliance burden for housing providers.
High-performing vs poorly performing heat network
source: Heat network optimisation guide by DESNZ
Thermino heat batteries work well with heat pumps
In a heat network scenario, heat pumps, paired with traditional hot water cylinders, often struggle under peak domestic hot water demand, particularly compared to the point-of-use gas or electric boilers which quickly heat water on demand. But when paired with compact thermal storage (as well as charged during off-peak or using rooftop PV generation), hot water can be delivered on demand efficiently. This load-shifting approach can also bring significant savings in operating costs and energy use.
For networks already designed around high temperature heat pumps, Thermino offers an ideal fit that doesn’t require a system redesign.
Proven success with Sunamp in real heat-network retrofits
Thurrock Council: Tower block retrofit tackling fuel poverty
Three high-rise blocks with outdated electric storage heaters were retrofitted with ground-source heat pumps and Sunamp Thermino batteries. Residents’ bills dropped by 67% and carbon emissions by 70%. One tenant said they went from spending £75 to £21 a week – “it’s so cheap to run.”
Supported by the Social Housing Decarbonisation Fund, this project shows how compact thermal storage paired with ground loop arrays cuts costs and carbon without tenant disruption.
Gentoo Group, Sunderland: Swapping out gas boilers
Gentoo replaced gas in 364 high-rise flats with ambient loop networks, in-flat ‘Shoebox’ heat pumps, and Thermino heat batteries – all without decanting tenants.
The switch wouldn’t have been possible using hot water cylinders due to space constraints in the flats. The result: 420 tonnes of CO2 savings per year, no Legionella risk, and low maintenance. Residents gained quiet hot water systems and landlords avoided gas safety checks and high maintenance overheads.
Historic church conversion, Edinburgh
Lar Housing Trust turned a 125-year-old church into townhouses and flats, using boreholes, Shoebox heat pumps and Thermino for hot water. No external units, no rooftop ASHP kits, just compact thermal storage inside each new build flat.
Thermino’s modular shape enabled fitting into different property sizes – while time-of-use charging enabled residents to store heat in Thermino heat batteries when it’s cheapest. A great case of architectural integrity meeting smart decarbonisation.
EastHeat Project, Scotland: Solar paired with thermal energy storage at scale
Backed by the Scottish Government’s Local Energy Challenge Fund in 2016, EastHeat was the largest residential heat storage project in Europe at the time. The project had over 700 Thermino heat batteries installed across 625 homes, most of them off-gas grid, replacing direct electric heating and hot water systems, and in some cases, working with solar PV and heat pumps to cut reliance on gas and grid.
The trial included range of properties: flats and houses, rural and urban, managed by Castle Rock Edinvar (now Places for People) and East Lothian Housing Association.
The next gen of heat networks needs compact hot water system to enable renewables
As the UK transitions towards net zero, heat networks will play an increasingly critical role in decarbonising the social housing sector. Their success depends not just on the heat source but also on how heat is stored and delivered at the dwelling level and the ancillary hot water system.
For specifiers, that means designing for heating efficiency, tenant wellbeing, and regulatory readiness from the outset. And that includes rethinking hot water – energy consumption (about 18% of UK’s average household energy consumption) and the space it occupies in a flat.
Thermino provides a future-ready alternative to a traditional hot water cylinder – compact, efficient, Legionella-safe and proven in UK high density tower blocks.
It reduces standing heat losses, simplifies compliance, and enhances tenant comfort – all while fitting into tight retrofits and modern modular builds.
With Ofgem’s new regulatory oversight and HNTAS 2025, now is the time to ensure that social housing heat networks are designed not just to meet targets but also to deliver for the people who live in them.
To support integration into your design process, Sunamp offers BIM models & SAP technical notes (available here) to help you assess compatibility and performance in your projects.
Need help evaluating project fit? Click here to get in touch with our technical team to discuss how Thermino can work for your next housing development or retrofit scheme.
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