These Finnish homes are being heated by a surprising source: Bitcoin
For someone who cares about climate change, Matt Carlsson had what seemed like a dream job: teaching his clients how to decarbonize buildings. But he was frustrated. He could give his clients the tools to improve their energy efficiency and phase out fossil fuels, but if they couldn’t easily turn his advice into cost savings, they would simply ignore him.
“Most of these people won’t act,” he realized, “because there won’t be a business case.”
Carlsson decided he would need to find a job where he could advocate for energy efficiency in economic terms. This led him to a surprising place: Bitcoin.
Bitcoin mining releases a huge amount of heat. Indeed, the “mining” in question refers to the energy-intensive computing process by which Bitcoin transactions are verified. In a typical transaction, a square computer attempts to solve what is essentially a very complex mathematical problem. If he manages to do this before any other “miner” working on the problem around the world, the miner is rewarded with his own bitcoin.
This process requires a lot of energy; Overall, bitcoin mining accounted for about 0.5% of global electricity consumption in 2024. The more complex the task at hand, the more electricity is required and the more heat is created. Essentially, as long as it’s lucrative to mine bitcoin, it’s going to generate a lot of extra heat as a byproduct. The question becomes: can this heat be used for beneficial purposes?
This is where Carlsson comes in. He now helps heat the homes of 80,000 people in Finland with waste heat from local cryptocurrency miners, as part of a project led by his new employer, bitcoin mining company MARA Holdings.
Water flows through MARA miners, which are stored in black metal units in the centers of cities, cooling them before exiting at a searing 122 to 172 degrees Fahrenheit (50 to 78 degrees Celsius). From there, water is pumped underground through the city’s existing district heating systems, significantly reducing the need for traditional boilers. As a result, MARA’s two Bitcoin districts have avoided greenhouse gas emissions roughly equivalent to those produced by 700 U.S. households since its first project went live in 2024.
Carlsson thinks this model could be extended to cities and buildings around the world – and he’s not the only one. Joint bitcoin mining and heating operations are popping up across Finland, an ideal location due to its cool climate and existing district heating systems that businesses can easily connect to. Terahash Energy’s “Genesis” project, for example, sends waste heat from bitcoin mining to an industrial area in the Nordic nation, as well as to some nearby homes. Global Bitcoin mining infrastructure company Hashlabs hosts six sites connecting miners to district heating systems elsewhere in Finland, with more in the works.
“It’s a business after all,” said Alen Makhmetov, co-founder of Hashlabs. “I just want to make our business much more sustainable, robust and long-term,” he said. Although there are also climate arguments in favor of the operation, Makhmetov means “sustainable” in the economic sense of the term. This is because Hashlabs is now safe from a fall in the price of bitcoin: if they lose crypto revenue, they will still get revenue for their heating services. Heating customers are also isolated: Hashlabs has promised to continue producing heat, even if the value of bitcoin makes its mining unprofitable.
“It was really obvious: why not do that?” said Adam Swick, MARA’s chief strategy officer. In effect, MARA generates two sources of income: they earn bitcoins through mining, of course, but the districts also pay them fees for heating, while receiving free water needed to cool their miners. Each of MARA’s Bitcoin heating systems is sized to provide the minimum heat needed all year round in the cities where they operate. (In winter, districts use a combination of electric and biomass boilers to provide supplemental heat.)
Residents of the two localities where MARA operates, the Satakunta region and the town of Seinäjoki, may not realize that anything has changed, because they receive heat from the same pipes that they always have. “That’s kind of the goal, that no one gets hit,” Swick said. MARA has covered all equipment costs and provides heating at a lower price than electric heating companies.
In MARA’s eyes, it is also better for the climate. District heating systems in Finland are mainly powered by the combustion of biomass, such as wood chips. Although biomass is considered renewable by some, including the European Union, it still emits carbon when burned. (In both locations where MARA installed its bitcoin miners, the districts were also burning peat.) By reducing the amount of biomass and peat the districts must use, MARA estimates that it has mitigated nearly 5,000 tons of greenhouse gas emissions over the 1.5 years its districts have been operating. (To arrive at this count, the company references the latest official count of emissions caused by electricity production and consumption in Finland to determine how many emissions are caused by miners, and then compares that to emissions from traditional district heating in Finland.)
This power plant has stopped burning fossil fuels. Then Bitcoin came along.
But this project will not make sense for all district heating systems in the Nordic country, because many of them are already very efficient. Nearly half of them get their heat from cogeneration plants or power plants that already burn fuel for the electricity grid. These systems “harvest that heat to be as efficient as possible,” said Eric Bosworth, founder of Thermal Energy Insights, where he advises on projects to transition gas heating systems to low-carbon thermal energy networks. This weakens the case for heating with Bitcoin.
And even where it is not possible to use waste heat from cogeneration plants, reusing heat from bitcoin mining is by no means the ideal form of efficient heating – although it is undoubtedly better than wasting it. Bitcoin miners use the same amount of energy as an electric resistance water heater. Essentially, one unit of energy in produces one unit of heat out. This pales in comparison to the efficiency of electric heat pumps.
But even though converting to heat pumps would be much more efficient, it would require costly overhauls; each individual building should install a heat pump and associated infrastructure. Most existing systems are not prepared to support these costs – another version of the dilemma Carlsson faced before joining MARA.
However, when district heating systems find themselves overly dependent on imported fossil fuel sources, bitcoin waste heat can offer a cost-effective solution accompanied by a plausible climate case. Hashlabs secured its first contract for a Bitcoin heating district after Russia invaded Ukraine, sending energy prices skyrocketing. Some district heating plants that relied on natural gas had gone bankrupt and “had to close their doors or innovate,” Makhmetov said. Bitcoin mining offered a cheaper solution – one that provided heat with far less need for fossil fuels.
Of course, it’s easy to argue that the best thing to do than efficiently use bitcoin’s waste heat is to not mine bitcoin at all. Of all forms of cryptocurrency, bitcoin consumes the most electricity – more than a small country – because of the particularly energy-intensive way it verifies transactions, called proof of work.
Given that most electricity grids today still run primarily on fossil fuels – unlike Finland, which is almost 95% powered by carbon-free sources, including nuclear and biomass – this could seriously limit the climate case for mining Bitcoin to exploit its waste heat.
“It’s not a bad thing to be able to heat homes affordably,” said Johanna Fornberg, a senior research specialist at the environmental advocacy nonprofit Greenpeace. “But does that actually provide justification for the industry? I would say no.”
“We want to avoid believing these claims that Bitcoin provides a solution where there is none otherwise,” she added. Greenpeace, along with other climate organizations, have advocated for Bitcoin to change its verification method, which would significantly reduce its energy consumption.
In a world where decarburization Efforts often involve trade-offs, Carlsson is happy that, in this case at least, bitcoin mining produces what seems to him to be a win-win solution.
“When I first started learning about Bitcoin, I was wary of it and trying to figure out if it was a scam,” he said. Seven years later, two tiny miners sit on his desk. “Now I feel like a missionary, part of a strange cult.”
Still, if operations like MARA’s expand further, it could mean fossil power plants in Finland will have to operate more, increasing overall emissions, just to have enough energy to power bitcoin mining, Bosworth said. “I think the more valid argument is that if a Bitcoin operation is already planned, then that heat should absolutely be harvested and sent to a district when possible,” he said.
A reduction in energy consumption resulting from the reuse of waste heat from mining “is rather a positive side effect that largely has a negative impact on the climate,” Fornberg said, “and not something we want to encourage and increasingly depend on in the long term.”
