This innovative project promises to decarbonize the heating of an entire city

In addition to distributing heat without any carbon emissions, the project will also offer citizens and tourists tropical forests and hot water pools.
Hot Heart

Hot Heart is an innovative project that promises to decarbonize Helsinki’s heating. Unveiled in March 2021, it will also offer citizens and tourists tropical forests and hot water pools.

Hot Heart was one of the winners of the Helsinki Energy Challenge, which was launched to find a solution to one question – “How can we decarbonize the heating of Helsinki, using as little biomass as possible?”

The Hot Heart system comprises of 10 cylindrical reservoirs of 225m (~740 feet) diameter. These reservoirs will be filled with approximately 10 million cubic meters of hot water. To do this, Hot Heart will first use energy from existing renewable sources, converting them into heat using seawater heat pumps. Then, it will store this thermal energy in the reservoirs for when it is needed.

Finally, the reservoirs will be connected to Helsinki’s existing district heating system in order to distribute heat across the city at lower prices, without any carbon emissions. On its website, the Helsinki Energy Challenge explains that by the end of the decade, Hot Heart expects to cover the full heating demand of the city (6,000 GWh).

Hot Heart diagram

Additionally, the project will also attract tourists as four of the ten cylinders will house all-year tropical forests and hot water pools at sea — all while embodying various elements of Finnish Culture: islands, nature, etc.

The Hot Heart project aims to become known as “the Helsinki model” by 2028. In other words, it hopes that by the end of the decade, other countries will be able to apply the system to their own cities in order to benefit from its numerous features.

This project has been developed by a diverse and multidisciplinary team as Carlo Ratti Associati (Italy) collaborated with Ramboll (Finland), Transsolar (Germany), Danfoss/Leanheat (Finland), Schneider Electric (Finland), OP (Finland), Schlaich Bergermann Partner (Germany) and Squint/Opera (UK).


The Hot Heart project was one of the winners of the Helsinki Energy Challenge, which was launched to help decarbonize heating systems in Finland's capital by 2030.

Expected to be fully implemented in 2028, Hot Heart consists of a series of islands that store thermal energy and can support tropical forest ecosystems from all over the world. The islands are actually 10 basins that are cylindrical in shape. Each measures 225m (~740 feet) in diameter. The basins serve as hot water reservoirs that are capable of storing millions of gallons of water. The system works like a thermal battery.

Four of the 10 reservoirs are enclosed in transparent domes, and this is where the floating forests will thrive. These tropical ecosystems will serve as social gathering spots, and the domes will be warm even during the harsh Helsinki winters.
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Action point

If you're a public official dreaming to leave something behind your tenure at your municipality, you may want to consider a big and bold project like Hot Heart. It, obviously, will require co-operation and coordination between multiple parties, but at the end of the day - it will be well worth the effort. This is a green project that also saves money, though the initial investment required for it may be too much for smaller towns. Except if they find a way to export their heating to nearby cities.

A project like Hot Heart is something that can hardly be achieved by any single company. Rather, it requires a team effort and a lot of money. Perhaps a federal government could help fund it or perhaps it could be a public-private partnership. In any case, this is a challenging project only the brave and bold (and well-capitalized) companies can dive into. Having a case study, or at least an approved project from Finland, may help you push something like this to municipalities your business serves.