Heat Pumps in District Heating and Retrofit


12 March 2024

In the second article in the series panel expert at REHAU Retrofit 231 event, Simon Eddleston, Construction Director at Switch2 Energy discusses retrofitting homes, in particular looking at district and communal heating technologies and the benefits to end-users as a result of their retrofit work.


The government aims to significantly increase the share of total heat derived from heat networks by 2050 as part of the transition to net zero. With this comes huge potential for investment, innovation and low-carbon technology advancement.

Under this decarbonisation strategy, the UK Government plans to expand the sector by 2050, so that heat networks supply 18% of total UK domestic heat, compared to 2% today.

If we are to reach such an ambitious target, it is clear that relying on new- build schemes alone will not be sufficient. Therefore, retrofitting heat networks into existing homes and developments has a huge part to play in achieving the adoption of these technologies at scale.


Heat Networks

Communal and district heating networks are heating systems that provide low-carbon and renewable heat energy to multiple buildings or properties from a central energy source via a network of insulated underground pipes. Heat networks offer a sustainable, holistic approach to energy distribution, which can deliver cost-effective and reliable heating to communities, as well as commerce and industry. They will also play a key role in the decarbonisation of heating, as a central heat source can be much more easily upgraded as new, low-carbon technologies are developed, and it can be used to harness heat from renewable sources as they become available, for example waste water heat recovery.

Communal heating is the term that is usually used to describe the supply of heat to a community of homes comprising typically buildings within a campus-style development with multiple dwellings, such as a multi-storey tower block or housing complex.

District heating is the term that is used to describe larger scale distribution of heat across multiple boundaries larger in scale, delivering heat to multiple developments, across a city including homes, businesses, and public buildings.

There are four main components of a communal or district heating network:

  1. Heating or cooling energy centres: These are the central sources where heat or cool air is generated, and renewable energy captured
  2. Distribution network components: The pipework and infrastructure that helps distribute the heating or cooling energy from the central source to the end users.
  3. Customer installations: These include thermal loads, energy storage systems, metering and control systems
  4. Heat Interface Units and consumer heating: The wet heating system within buildings connected to the network. Heat Interface Units connect the network to the heat emitters e.g. radiators in the homes of consumers.


Retrofitting heat networks into existing developments is crucial if the country is to meet its targets and to keep on track with the decarbonisation of domestic heat.

Central to any of Switch2’s retrofit projects are the residents impacted by the works. This isn’t about hitting targets or meeting planning requirements – at the heart of every project must be an assurance that residents will be able

to heat their homes, in a way that is intuitive to them, and more efficiently and affordably.

From the consultation stage, all the way through to design and build, in any project we work on there is a clear journey for residents to go on to become our customers. As part of our onboarding, it’s essential for us that residents understand how the technology works, the benefits to them in terms of cost, and more practically, how their billing will work.

As an operator, we have explored several ways of retrofitting communal heating systems into existing housing stock – I will set out three examples of what this can look like in practice.


Extension of existing networks

In 2017 we were approached by one of our existing supply partners in London, to operate a community energy network on their behalf. The council expressed a desire for their existing heat network to be expanded to reach additional houses around the periphery of the network to meet their target of connecting 4,000 homes across the borough to the network by 2025. The existing network already covered a significant number of residential and commercial buildings, but the council recognised an opportunity to deliver more low-cost heat to individual houses around the footprint of their network.

The process involved connecting non-heat network homes - mostly small residential terraces - to the existing network, replacing their conventional gas boiler and connecting the heat source to existing radiators within homes. Much like the combi-boilers they were used to, the heat network delivers instant heat. This means that the system works intuitively for residents and heats their homes without the need for them to learn how to use new tools or technologies. The removal of gas from their homes meant they no longer had to undertake annual maintenance on their gas appliances, with the new HIU coming under the responsibility of Switch2.

Additionally, with the installation of electronic Heat Interface Units within homes, heating can be externally monitored to ensure that the system is working properly and that residents are keeping warm and healthy.

Our connected ICON Heat Interface Unit allows for monitoring, adjustments and maintenance to be carried out remotely. This means that residents do not have to book maintenance works themselves and ensures optimal efficiency of the network as a whole, while reducing maintenance costs and increasing reliability.

There is enormous potential for this kind of retrofit, particularly in urban areas such as London, where non-heat network homes adjacent to existing networks can be easily connected with minimal disruption or expenditure.



Switch2 has also carried out retrofit works on more common housing over a smaller scale. These properties are generally high-density, 1970s-built tower blocks with shared spaces, operating on electric heating.

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There are many examples of heat network retrofit works done alongside a range of other refurbishment, retrofitting or building safety improvements cutting project costs and minimising disruption to tenants.

As a resident-focused energy company, we have been involved in many of these schemes, and are well placed to facilitate the process of tenant management and engagement.

The incorporation of metering alone can reduce consumption by typically up to 50%. There is also significant funding available for heat network retrofitting works of this type, available through the Public Sector Decarbonisation Scheme2. The scheme, which is providing over £1.4 billion of grant funding until 2025, incentivises a ‘fabric first’ approach – maximising the performance of building components used during the design phase. If undertaking efficiency or insulation upgrades in a building’s shared space, funding from the scheme could be utilized to fund a new low-carbon communal heating system within the property.


Decant and rebuild

As a company we have also been exploring retrofits where a developer or housing association has decided to regenerate a whole area; knocking down a collection of buildings under a phased regeneration plan providing the opportunity to incorporate low carbon heating as part of the rebuild plan, and onboarding residents in phases.

In one example of such a scheme in London which is already underway, there is a commitment to develop a community of 3000 homes where buildings are rebuilt in phases, with residents decanted throughout the process. This means that from the outset energy sensors and a communal heating system can be installed alongside the development of the buildings meaning that it is ready to go as soon as works are completed.

In a project such as this, the energy centre is managed and scaled so that it remains efficient throughout, with capacity increased as the community grows and new homes are connected.

Switch2 is technology agnostic and takes an environment-led approach to any retrofit works, so will use the technology that is right for each environment. While this retrofit scheme in a more high-density environment utilises air source heat pumps for its energy centre, in a lower-density environment it can be beneficial to use ground source technology.

As a founding member of Heat Trust3, the consumer champion for heat networks, all of our networks operate within this frame of governance placing customers at the heart.

Residents must be considered before, during and throughout the retrofit process. It’s vital that, from the consultation stage onwards we work with tenants so that they can make informed choices when projects are designed and built.

In an unregulated heat network sector, transparency and a customer-focused approach are key for us as an operator, so any retrofit projects must start and end with the resident.




In the next issue, we will hear from Steve Richmond, Head of Marketing & Technical at REHAU, who will offer his technical expertise on district heating, alongside wider industry challenges and the policy landscape.



  1. www.buildingcentre.co.uk/whats_on/exhibitions/retrofit2023
  2. www.gov.uk/government/collections/public-sector-decarbonisation-scheme
  3. www.heattrust.org