Sources of heat

Heat Trust's customer protection standards for heat networks do not specify fuel source, so any heat network no matter the fuel type can register with us. To find out more about registering with Heat Trust please see our supplier pages, or for more information for customers please see here. 

Heat networks can source their heat from any fuel or generation process; this is sometimes known as being fuel agnostic.
Typical examples of heat sources for heat networks are: gas boilers, Combined Heat and Power (CHP) plants, wasted heat (from industrial processes, wastewater treatment etc.) and biomass fuelled boilers. More heat networks are now being heated by technologies such as large-scale heat pumps (usually water or ground), geothermal sources or even underground transport. We have highlighted some examples of these in the UK below. There are also projects in development in the UK and operational internationally using waste heat from mine water, deep geothermal, data centres, greenhouses and large-scale solar thermal (often with seasonal thermal stores) to power heat networks.

Heat networks can also make use of thermal stores (large insulated tanks of hot water). These can either provide heating temporarily if the primary source of heat fails, therefore increasing the reliability of supply for customers; or they can supply heat at a time of high demand on the fuel source to help balance out demand. The time these can supply heat for depends on the size of the store, ranging from a few hours with small tanks to between seasons with large ground pits.

Gas

Currently most heat networks (90%) use gas as their primary fuel source, typically through one or more gas-fired boilers. The gas is usually sourced from the national gas grid, and of the UK’s total gas demand in 2018, about 50% came from the UK’s contintental shelf and 50% was imported. However 'biogas' from anaerobic digesters, e.g. at sewage treatment works, can also provide the gas fuel for heat networks.

Some gas boilers produce only heat, like individual property boilers, however some produce electricity  (burning the gas to create steam which turns turbines) and capture the excess heat at the same time. This is known as a Combined Heat and Power (CHP) plant (which can also use fuels other than gas) and is often more efficient than generating electricity or heat independently of each other.

Wasted heat

Many industrial processes generate heat as a by-product, such as incinerators, underground transport and sewage treatment works. Heat networks can make use of otherwise wasted heat by transporting it to an end user that requires heat. This is often limited by the end-users of heat not being close enough to the source of wasted heat.

Energy From Waste (incinerator)

Waste from transport

The London Underground produces waste heat, mostly from friction of the trains on the rails. Through adding a heat pump, the temperature of the heat captured can be raised to provide heating to a heat network.

Waste heat from sewage treatment works

Some of the processes used to treat wastewater, including sewage, involve anaerobic digestion of organic matter within the waste water, which generates heat as well as producing gas.

Biomass

Biomass usually comes in the form of wood pellets burned in a furnace. These wood pellets can come from waste/off-cuts from the wood industry or virgin woodland.

Heat pumps

Heat pumps capture heat energy from either ground, water or air, and then through a pump powered by electricity increase the temperature to heat homes and buildings. This increase or ‘upgrade’ in temperature works in a similar way to how a fridge is cooled but in reverse. Heat is generated through rapidly increasing the pressure of refridgerant gasses in a contained space, this increases the temperature of the gases, which can pass to adjacent water or air, piped onwards. At the scale of heat networks, only water or ground source heat pumps tend to be used.

Water Source

Ground Source

Geothermal

In the UK the top 10 - 15m of ground is heated by the sun and acts as a thermal store. By running pipes of water through the ground at these depths, the heat will be transferred to the water, which can then go on to heat people's homes. In some places, such as Iceland, the heat from volcanic activity (and heat conducted upwards from the Earth’s core and mantle) can be captured, which have much higher temperatures.

Geothermal is different to ground source heat pumps because electric pumps aren't used to raise the temperatures, and their pipes tend to go deeper into the ground.

If you know of an operational heat network in the UK heated by an innovative low carbon fuel source then please let us know via our contact page.

Heat Network related documents

Below is a list of some of the key reports about heat networks which you may have heard mentioned. It is not exhaustive, but might prove a good starting point if you want to learn more about the heat network market and the governments’ positions on heat networks.

They are ordered by release date, with most recent first.

Heat Trust Reports

Heat Trust Annual Report 2020 - Heat Trust (August 2021)

This is our fifth annual report. It presents complaints and interruptions statistics as well as other data from both Registered Participants and the Energy Ombudsman from 2020. In addition it sets out the importance of Heat Trust in the current stage of statutory regulation development, and an overview of our latest activity.  We are pleased to see membership increase but continue to work towards supporting more of the heat network industry to offer minimum protection standards to their customers.

Heat Trust Annual Report 2019 - Heat Trust (May 2020)

This is our fourth annual report. It presents analysis of data from both Registered Participants and the Ombudsman from 2019, as well as our reflections on the first four years of Heat Trust and recommendations for developing regulation which draw on this experience. We are pleased to see that the voluntary standards set by Heat Trust are having a positive impact on the market and delivering improvements to customer experience.

Heat Trust Annual Report 2018 - Heat Trust (November 2019)

This is our third annual report. Heat Trust now provides protection to 10% of the market. Reflecting on the experience gained over three years, the report sets out the key principles to consider as regulation of the market is developed. The report also provides a summary of performance of heat networks registered with Heat Trust over the previous three years, including complaints from the Energy Ombudsman, interruptions and debt and disconnection.

Heat Trust Annual Report 2017 - Heat Trust (November 2018)

This is our second annual report. The report provides a summary of the performance of heat networks that are registered with Heat Trust, and an update on Heat Trust developments and activities. It also provides greater detail on interruptions and complaints data, and case studies from complaints that went to the Energy Ombudsman, the independent dispute resolution service.

Heat Trust First Annual Report 2016 - Heat Trust (October 2017)

This is the first annual report from Heat Trust. It summarises the performance of heat networks that are registered with Heat Trust, and draws out key findings from the first year of operation.

Other Reports

Existing Legislation

The Heat Network (Metering and Billing) Regulations 2014 with a few amendments made in the Heat Network (Metering and Billing) (Amendment) Regulations 2015, was made UK law from the requirements regarding the supply of distributed heat, cooling and hot water as part of the EU Energy Efficiency Directive requirements.

Key requirements include:

• heat suppliers have a duty to notify their network to the Government
• meters must be installed to measure consumption of heating/ cooling/ hot water, where cost effective and technically feasible, and install a heat cost allocator where not
• sending a bill at least once a year, based on actual consumption where possible, and containing clear explanations of how the bill was calculated, amongst other billing information

Government Support

UK Government

The government has produced guidance for suppliers on how to follow these regulations. More general information about heat networks can be found on the Government website pages here: https://www.gov.uk/guidance/heat-networks-overview, including their support provided for heat networks through two key mechanisms: HNDU and HNIP.

The Heat Networks Delivery Unit (HNDU) was established in 2013 to address the capacity and capability challenges which local authorities identified as barriers to heat network deployment in the UK. The Unit provides funding and specialist guidance to local authorities who are developing heat network projects.

The Heat Networks Investment Project (HNIP) is delivering £320 million of capital investment support to increase the volume of heat networks built, deliver carbon savings for carbon budgets, and help create the conditions for a sustainable market that can operate without direct Government subsidy. The pilot phase of the Heat Networks Investment Project ran for 6 months and awarded £24 million to 9 successful Local Authority projects in March 2017.

The Green Heat Networks Fund (GHNF) is due to replace HNIP and was consulted on in early 2021. It is a capital grant funding programme which is intended to help new and existing heat networks to move to low and zero carbon technologies. Its objectives are to: achieve carbon savings and decreases in carbon intensity of heat supplied, increase the total amount of low-carbon heat utilisation in heat networks (both retrofitted and new heat networks) and help prepare the market for future low-carbon regulation and ensure compliance with existing regulations (such as the Heat Network (Metering and Billing) Regulations, Heat Network Market Framework and the Future Homes Standard).

Scottish Government

The Scottish Government have lots of information about heat networks and their context in Scotland on their website here, including links to their Heat Map.

There is also a dedicated website for district heating set up by The Heat Network Partnership, which aims to boost the uptake of low carbon heat technologies in Scotland and focuses the efforts of a number of agencies working in this area.

The Heat Networks (Scotland) Bill, setting out regulation of heat networks in Scotland, has now been passed. For more details see our Regulation update page.

Further information will be added soon.

What is a heat network?

A heat network is the system of insulated pipes which transports heat from a source (or multiple sources) to more than one end user. The UK government has stated that heat networks will be used more frequently to heat our homes and businesses. In short, heat networks form part of new energy infrastruture, vital in supporting the move to a low carbon energy system.

They are natural monopolies which means that one organisation is the supplier for all properties on a single heat network.

There are two types of heat networks: district heating and communal heating.

• Communal heat network:Communal heating is the supply of heat and hot water, from a source usually known as the energy centre, to a number of customers within one building only. The energy centre often consists of a large boiler in the basement of a building with the heat and hot water distributed through the building via a series of pipes.

• District heat network: District heating involves a local energy centre that supplies heat and hot water to customers in more than one building. District heating networks can range in size from a few hundred metres supplying just a few homes to several kilometres of pipe supplying heat and hot water to multiple buildings in a development.

According to market data collected by government, most heat networks are actually communal heat networks (85%).

Some new heat networks are built for large projects which are completed in stages. This might mean that some residents will move in to their homes before others are built, which will be joined to the heat network when completed.

Who would be a heat network supplier?

Heat Trust defines the heat network supplier as the organisation that is contracted to provide heating and/ or hot water to each property – they would provide the Heat Supply Agreement (or customer charter) to each occupant on the heat network.

The type of organisations that fulfils this role can vary network to network. For example, this could be a:

• A dedicated heat network company (ESCO),
• The property developer,
• A housing association,
• A local authority,
• A community organisation,
• A management company,
• A company set-up by the freeholder to operate the network

All heat network suppliers that have registered one or more heat networks with Heat Trust can be found here.

Heat Interface Units (HIUs)

Some heat networks will include a heat interface unit within each property.

A heat interface unit (HIU) is the bridge between the communal or development-wide heat network and the individual property. It is a unit that brings hot water to and from the main heat network into each property.

There are two main types of HIU.

1. Heat-only HIUs – these are used on heat networks that only provide space heating to properties connected to the heat networks. The hot water is typically provdided by an electric immersion heater and hot water tank.
2. Heat and hot water HIU – these are used on heat networks that provide both space heating and hot water to each property connected to the heat network.

There is now an industry standard for the performance of HIUs. More information can be found on the BESA website here: https://www.thebesa.com/ukhiu

Where are heat networks in the UK?

The database of registered heat networks in the UK[1], recorded that in 2015 there were just under 14,000 heat networks. Of these around 2,000 were district heating and 12,000 were communal[2]. These serve nearly 480,000 customers, providing around 2% of the UK buildings heat demand[3].

Heat networks require a certain density of heat demand in order to be economic. The geographical distribution therefore reflects that heat networks, and particularly district heating networks, are located in urban areas, new build developments and some rural areas.

BEIS map of heat network distribution in the UK by local authority.

Nearly 12,000 of all heat networks in the UK are in England (86%). 6% are in Scotland, 2% in Wales and 0.6% in Northern Ireland.

29% of heat networks were in London, and a further 14% in the South-East of England. Others are concentrated around Manchester, Birmingham, Newcastle, Sheffield, Bristol and Glasgow. Belfast has the highest proportion of heat networks compared to other regions in Northern Ireland.

Over 75,000 buildings are connected to heat networks. 80% of heat networks are connected to residential buildings. An even higher proportion of final customers are residential (92%)[4]. This reflects the higher proportion of communal heating networks, which are generally apartment blocks. 9% of heat networks are connected to education buildings, and 7% are commercial.

The majority of heat networks supply both space heating and hot water (70%), with only 8% supplying cooling as well.

Only 28% of final customers have meters. Scotland had the highest proportion of final customers with meters, at 40%, and Wales had the lowest (4%).

Of those who responded to the question (12,000), 32% billed their customers annually, 25% monthly, 16% quarterly and 27% responded with ‘other’, which could include Pay As You Go (PAYG).

Currently most networks (90%) used gas as their primary fuel source. The next most widely used fuel source was electricity (5%) followed by bioenergy and waste (2%). See our sources of fuel page for more information and some examples.

To find out which heat networks are registered with Heat Trust, click here. 

[1]https://assets.publishing.service.gov.uk/Government/uploads/system/uploads/attachment_data/file/712370/Energy_Trends_article_on_heat_networks_revised.pdf

[2] https://www.heattrust.org/images/docs/Docs_Copyright_Logo/Copyrighted-The-Heat-Trust-Fact-Sheet.pdf

[3]https://assets.publishing.service.gov.uk/media/5b55965740f0b6338218d6a4/heat_networks_final_report.pdf

[4] https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/712370/Energy_Trends_article_on_heat_networks_revised.pdf

Heat networks and climate change

In the UK approximately 40% of our energy consumption and 20% of our greenhouse gas emissions are due to the heating and hot water supply for our buildings.

Infographic from the CCC's Next Steps for UK Heat Policy Report, see below.

The UK government has legislated that we must recude greenhouse gas emissions to net zero by 2050. This provides the legal imperative to decarbonise the heat sector, which means that the UK will need to eliminate almost all emissions currently produced by heating and hot water consumption.

Heat networks are a part of our pathway to decarbonising heat, through efficiency of supply and the fuel source.

Economies of scale

It can be more economic to have one large heat generator and pipe the heat to many properties, than for each property to have its own generator, especially where there is a large capital cost associated with the heat generator (eg ground arrays for heat pumps). They are most efficient in heat dense areas, where pipes can be shorter between properties.

Fuel source

Heat networks are fuel agnostic, and so can be heated by any fuel. This includes low carbon heat generation from the beginning, or switch to an alternative source of heating at a later stage. See here for some examples of renewable sources of heat for heat networks in the UK already, from otherwise wasted heat to geothermal.

Additionally, thermal stores are increasingly used to balance demand swings and maintain supply during short outages. These are typically large insulated tanks of water that can store excess heat from generation at periods of low demand and supply heat at periods of high demand.

History

Heat networks have been widely used in Denmark since the 1970s, and are an established technology. However in the UK heat networks only supply 2% of current heat demand, having developed the gas grid to fuel boilers in individual dwellings as the main heating source since the 1970s. Please see our timeline of how the history of heating in the UK has developed.

Even so, around 13% of households in the UK are still not connected to the gas grid, where heating is supplied largely by oil heaters and sometimes electricity, or heat networks.

Future of heat networks

Scientific recommendations

The Committee on Climate Change (CCC) is the independent advisory body to the UK government on targets and progress made in reducing greenhouse gas emissions and preparing for climate change. The Committee identified what it calls low-regret routes to reducing emissions from heating buildings that the Government should pursue immediately which included “the roll-out of low-carbon heat networks in population-dense urban areas, along with energy efficiency and other measures”.

In its latest advice to the UK Government on the UK’s ‘carbon budgets’, the Committee recommended growth in heat networks, with up to 18% of heat demand met by heat networks by 2050 (see table below) from a current baseline of about 2%.

Their recommendations also included a major programme to build and extend low-carbon heat networks in heat-dense areas, connecting 1.5 million homes by 2030 and reaching 5 million homes by 2050.

This encompasses both retrofitting existing homes (there are about 29 million homes currently in the UK) as well as connecting new homes. This comes in conjunction with advice that after 2025, no new homes should be connected to the gas grid, and that new homes should have low-carbon heating systems instead.

The CCC also emphasised the expansion of non-domestic connections to heat networks, which in their ‘central’ scenario would account for 53% of total heat delivered by heat networks by 2050 (although only 28% of UK heat demand is non-domestic). Non-domestic buildings are largely concentrated in urban areas with a higher heat density, where heat networks are more likely to be deployed.

Government support

As part of their commitments to reducing their carbon emissions, the UK and Scottish governments are supporting the development of heat networks, through investment incentives and developing regulation which will support the sector.

The UK government department for Business, Energy and Industrial Strategy (BEIS) set out the context of the government’s support for heat networks and the role of the sector in the decarbonisation of heat in a report in December 2018. This responded to the CMA’s market study and the ADE’s Shared Warmth report on the heat network market.

Government acknowledged in the Clean Growth Strategy that they have set out a significant role for heat networks as a ‘low regregts’ component of meeting their decarbonisation commitments. They recognised that for the last 50 years we have largely relied on gas to heat our buildings, and heat networks are a key technology which can facilitate the transition away from fossil fuels towards low carbon energy sources.

See https://www.gov.uk/guidance/heat-networks-overview or our existing legislation section for more information on how the UK and Scottish governments are supporting heat networks. Also see our reports section for further reading on the development of the heat network market in the UK.

If you’re thinking of moving in to a home or building heated by a heat network - these are our top questions to ask before you decide:

• Is the heat network registered with Heat Trust? If not, are there plans to? (this will ensure you are provided with minimum customers standards that are comparable to the rest of the energy market and your supplier is audited.)

• What support do you provide for customers in vulnerable situations? (This can be specific for a situtation you already know about, or in general as any of us may find ourselves in unexpected situations at any time.) 

Bills 

• How do you calculate bills? (this is a potential source of confusion for customers who are used to other types of heating e.g. gas boilers or electric heaters)

• What tariff will I be placed on? What other tariffs are available to me, and how will you let me know if I’m on the best one for me? (Some suppliers may offer multiple tariffs, some might only offer one)

• How can I pay my bills? And how often? (Heat network suppliers may offer different ways to pay, such direct debit, standing order or pay as you go, you may be able to pay at a local store or over the telephone to set up a regular payment)
  

• What happens if I can’t pay my bill? (suppliers should be able to talk this through with you and either point you in the direction of some independent debt advice, and/or set up a repayment plan which should make paying your bills more manageable) 

Meters 

• Is there a meter for my property? (All new build properties are required by law to have an indiviual meter for each property. For older properties there may only be a meter for the building, not for each individual property)

• Do I need to submit meter readings? (some meters do this automatically, others require the customer to send in meter readings to their supplier at regular intervals; this may be via telephone or online, or another method)

• Will I have a smart meter? (this may show you more detailed information about your consumption patterns)

Contact

• If something goes wrong...What are your emergency/ outage response times? Do you provide compensation if these last for a certain period of time, and what is the level of compensation? (in case something goes wrong, it is useful to know how quickly you can expect it to be fixed)

• How can I contact you? For emergencies, outages, enquiries or complaints? (this could be telephone, email, text, online webchat etc.)
• Do you hold drop-in sessions for customers or developers? (this can be in many forms but offers an opportunity for face-to-face questions and answers)

• What do I need to do when I move in to set up my account with you? Or when I leave? (this could include providing your details and date of moving, as well as meter readings)

• What is your complaints policy? (All customers should be provided with information on how they can raise a complaint, how the complaint will be managed and what independent redress is in place, if the supplier can not offer a satisfactory resolution.

Download our factsheet for a summary of our key standards.