Could London's lost rivers provide heat for the city?

Take a stroll down London’s Farringdon Street, and you’ll see cars, buses and bikes. But wind the clock back a few hundred years and you’d be traveling down the river Fleet. In centuries past, a myriad of tributaries flowed right through London into the River Thames.

From the River Tyburn coursing through the West End to the River Effra flowing through Brixton up to Vauxhall, at one time these waterways powered the city. They provided water for drinking and cooking, opportunities for transportation and power for driving mills.

They were also a cracking place to chuck your sewage into. And as the metropolis grew, this was one of the major reasons they were covered over and built on top of.

But what if we could use them to power our city once again? Through the magic of heat pumps, London’s lost rivers could provide low cost, low carbon heating and cooling to the buildings above. They could help us solve the big challenge of decarbonising heat.

There’s huge potential for London’s lost rivers to provide clean, efficient and reliable heating for the city - tackling climate change and air pollution. And of course the same technology can be used in other underground waterways like sewers in towns and cities across the country.

Working with consultants Scene, we’ve looked into this idea. We’ve prospected five locations where lost rivers could be used heat the buildings above.

Low carbon heat with heat pumps

One of our great challenges in tackling climate change is decarbonising heat. We’re miles off our targets, and gas-fired boilers rule the roost across the country. As we move to 2050, heating for space and water will need to be completely decarbonised to meet our carbon budgets.

The first step is to massively improve the energy efficiency of buildings. That way we’d need less heating (because we’d be using what we have more efficiently, but we’d still need some. Right now, using electricity for heating seems like the best solution. Enter the heat pump.

Heat pumps use electricity to harvest low-grade heat (as in not-very-hot-heat) from the surrounding area and use it to heat space and water in buildings. It’s essentially moving heat from one place to another, using some simple physics to amplify its effects. Putting just one unit of electrical energy in will produce three to five units of heat energy.

What about low carbon cooling? Heat pumps look pretty good here too - the same device can be used to provide heating in winter and cooling in summer. Not bad.

Heat pumps can gather heat from a few different places: the air, the ground, and water. Some can power just one or two houses and others whole streets, businesses and shopping centres.

Read more about how heat pumps work

It’s not as simple as whipping out your gas boiler and plugging in a heat pump. Heat pumps work best when draughts are plugged, so major energy efficiency upgrades are needed. Plus, pipes and radiators will need upgrading too. But, a report commissioned by the Mayor of London estimated that 38% of London’s total heat demand could be met in this way without lots of refurb.

Where it’s happening already

Gathering heat from underground waterways is not a new idea. Here are two examples of buildings already doing it.

Borders College, Scotland

In 2015, the Borders college campus at Galashiels became the first place in the UK to install a heat pump in a sewer. The system extracts heat from the waste water flowing into a local treatment works and provides heating and hot water. It should meet 95% of the college’s heating needs.

State Ministry Building, Stuttgart, Germany

In 2012, a new building for Baden-Württemberg’s Interior Ministry was constructed. It sits right on top of the Nesenbach, Stuttgart’s very own lost river which now flows underground. The building was designed to be super energy efficient, but the small amounts of heating and cooling it needs are provided by a heat pump in the Nesenbach.

Where it could happen next

Together with energy experts Scene, we’ve poured over maps, gathered river flow data and searched for heat demand info. Here are five places we’ve prospected that could use a lost river to power their heating.

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Buckingham Palace

Yep - for real.

Buckingham Palace has just started a big refurbishment to modernise the heating, plumbing and wiring and to cut their carbon emissions by 40%. They’re planning to install a biogas boiler, but that will only provide 5% of the palace’s heating and hot water.  In other words, Her Majesty could do with some more low carbon heat.

The River Tyburn flows from Hampstead, under Regent’s Park and into Green Park. Just 250m north of the palace there’s a heavy flow of water. And lots of flow means lots of potential heat to be harvested.

A heat pump here could produce far more heat than the palace uses even on the coldest day! Of course in such an old building it’s unlikely they could use all of that resource - the refurbishments needed would be mega. But the Tyburn could certainly going some way to keeping the royal family nice and toasty.

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Hammersmith Town Hall

Work is about to start renovating and rebuilding Hammersmith Town Hall. The plan is to pull down an 1970s extension and in its place build housing, a cinema, shops, offices and a public plaza.

Stamford Brook runs almost entirely underground. The brook is formed of three streams which come together at Ravenscourt Park. Until the early 19th century you could sail up lower part of the stream. Barges used to unload right where the town hall now stands.

50 metres south of the building there’s a large heat resource to be tapped. The council investigated the feasibility of including a heat pump in their plans, but sadly are unlikely to pursue it.

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Acland Burghley School

Every day 1000 students fill Acland Burghley secondary school, Tufnell Park. Over the winter, the school uses a lot of heat, racking up 100 tonnes of CO2 emissions per year and mega energy bills to match.

The River Fleet used to be one of the largest of the Thames’ tributaries - carrying boats and powering mills. One of its tributaries flows right near the school. A heat pump installed in it could easily meet all of the school’s heating needs - and more!

And get this. The school has 186 solar panels on the roof. They could provide half the electricity needed to run the pump - making it truly renewable heating.  

Somers Town Heat Network

Downstream of Acland Burghley School, the Fleet continues right by St Pancras Station. Across the road, a former ground-level car park houses the three gas boilers that currently power the Somers Town Heat Network.

This heat network provides heat to four nearby housing estates, and is being extended to supply another 184 homes, a school and a community centre.

Although the heat network is lower carbon than the individual gas boilers it replaced, it still uses gas. But, the buried River Fleet could provide about a third of the energy the network needs.

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Brockwell Lido

The hardy swimmers of south London don’t care, but Brockwell Lido falls to 2 or 3°C in winter!

The lido is right next to the lost River Effra. The Effra traces a route from Upper Norwood to Vauxhall Bridge via Dulwich, Herne Hill and Brixton. Urban legend has it that Elizabeth I and King Cnut both once travelled up the Effra.

Tapping into just one tenth of the heat resource of the Effra could keep the lido at a comfortable temperature for swimming in spring and autumn. By extracting a bit more heat in winter, the lido could get up to 25°C all year!

Let’s do this

Heat pumps installed in underground waterways have huge potential. Lost rivers criss cross London - and the same technology can be applied to drainage networks across the country. With the threat of climate change looming ever larger, we need to get moving on decarbonising our heating and heat pumps offer a smart solution. It’s time to take the plunge.


10:10 Climate Action is all about finding positive, practical solutions to tackle climate change. We’ve installed solar on schools, campaigned for better policy for renewables and looked for innovative ways for people to make the most of their local energy resources.

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We’ve produced a report with more details about our work and findings. Download it here.


Banner photo: Steve Walker, cc