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 centresgreenhouses 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.


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.

Name  Bicester Heat Network
Fuel Source  Gas CHP
Location  Elmsbrook, Oxfordshire
Size  800KWe CHP engine, 80m3 thermal store and back up gas boilers
Types of end users 393 zero carbon homes, a primary school, local shop, eco pub and community centre
Interesting facts Part of the UK’s first Eco-town, aiming to be zero carbon
Links to find out more



Name  Bristol Paintworks 
Fuel Source  Gas boilers
Location  Bristol
Size  8 x 250 kWe modular gas boilers
Types of end users  221 residential apartments and town houses, studios, offices, a café bar and exhibition venue
Interesting facts  It is a redeveloped paint and varnish factory
Links to find out more


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)

Name SELCHP (South East London Combined Heat and Power)
Fuel Source
Waste heat from incinerator (combusts waste from households to create electricity)
Location Southwark, London
Size 5km heating network for heat and hot water
2,500 Southwark properties
Types of end users   Residential
Interesting facts            It came from a consortium of three London Boroughs trying to tackle environmental problems and issues of landfill space, using waste that cannot be recycled for electricity generation
Links to find out more         


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.

Name Bunhill Heat Network
Fuel Source         Waste heat from London Underground (Northern Line)
Location Ventilation shaft of Northern Line of London Underground, Central Street
Size 1MW heat pump to heat an additional further 1,000 homes
Existing: 2MW CHP with large thermal store
Types of end users  Existing: 800 homes in Bunhill ward, as well as Finsbury Leisure Centre, Ironmonger Row Baths and offices on Old Street
Interesting facts Phase 1 has been in operation with a CHP since 2012. Phase 2 is to connect to the Underground in 2019.
During the summer months, the system will be reversed to inject cool air into the tube tunnels.
Links to find out more


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.

Name Stirling heat network
Fuel Source    Waste heat from wastewater treatment works and biogas CHP from the anaerobic digesters on site
Location Stirling, Scotland
Types of end users                               Key public buildings, including The Peak Leisure Centre, Forthbank Stadium, St Modan’s High School, numerous commercial offices and new build homes
Interesting facts

First CHP in UK to be used with heat from waste water pump system to deliver heat for a heat network.
It is expected to save around 381 tonnes of carbon a year.

Links to find out more



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.

Name Queen Elizabeth Olympic Park
Fuel Source Woodchip fueled biomass boiler for heat generation and a combined cooling, heat and power (CCHP) plant using natural gas
Location London, converted Olympic Park (2012 games)
Size Initial capacity of 46.5 MW of heating and 16 MW of cooling in two energy centres
16km heating network and 2km cooling network
Types of end users                 Olympic Park, the Westfield shopping centre, residents of East Village and the neighbouring area
Interesting facts

It is the largest decentralised energy scheme in the UK
It heated the Olympic Park and Village during the 2012 Olympic and Paralympic Games

Links to find out more


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

Name Queen’s Quay
Fuel Source 2 x 2.6 MW water source heat pumps, from the River Clyde
Location                  Clydebank, Glasgow
Size 2.5km of heating network
Types of end users       Local homes, businesses and public buildings such as West Scotland College and Clydebank Library and over 1,000 new homes
Interesting facts          First heat network powered by a river-source heat pump in Scotland
Links to find out more


Ground Source

Name Enfield Council: Ground Loop Array Heat Pump
Fuel Source Ground source heat pump
Location Enfield, London
Size 4km heating network
Types of end users 402 flats in 8 tower blocks
Interesting facts

100 boreholes capture the heat at depths between 197 – 227m
It replaced electric heating which was expensive

Links to find out more



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.

Name            Southampton District Energy Scheme (SDES)
Fuel Source  Large-scale CHP plant, supplemented by geothermal energy and conventional boilers; also provides cooling
Location        Southampton
Size Over 40 GWh of heat p.a
Types of end users TV studios, a hospital, a university, a shopping centre, a civic centre, residential buildings and a hotel – as well as public and private-sector residential developments.
Interesting facts Currently saving around 10,000 tonnes of CO2 emissions p.a.
Links to find out more