Shelves inside a cryptocurrency mining farm.Alexei Danichev/Sputnik/AP
This story was originally published by Grist and is reproduced here as part of the Climate Desk collaboration.
For someone who cares about climate change, Matt Carlsson had what seemed like a dream job: teaching clients how to decarbonize buildings. But he was frustrated. He could give customers the tools to improve energy efficiency and phase out fossil fuels, but if they couldn’t easily turn his guidance into cost savings, they’d simply ignore him.
“Most of these people are not going to take action,” he realized, “because there’s not going to be a business case.”
Carlsson decided that he’d need to find a job where he could make the case for energy efficiency on economic terms. This led him somewhere surprising: bitcoin.
Mining bitcoin throws off an enormous amount of heat. That’s because the “mining” in question refers to the energy-intensive computational process by which bitcoin transactions are verified. In a typical transaction, a boxy computer attempts to solve what’s essentially a very complex math problem. If it can do this before any of the other “miners” working on the problem across the world, the miner is rewarded with bitcoin of its own.
This process takes a whole lot of power; overall, bitcoin mining accounted for an estimated 0.5 percent of global electricity use in 2024. The more complex the task at hand, the more electricity is needed—and the more heat is created. Essentially, as long as it’s lucrative to mine bitcoin, it’s going to spit out a lot of extra heat as a byproduct. The question becomes: Can that heat be put to beneficial use?
“It’s not a bad thing to be able to heat homes in an affordable way. But does that provide justification for the industry?”
That’s where Carlsson comes in. He’s now helping to heat the homes of 80,000 residents in Finland with waste heat from local cryptocurrency miners, as a part of a project run by his new employer, the bitcoin mining company MARA Holdings.
Water runs through MARA’s miners, which are stored in black metal units in the center of the towns, cooling them off before coming out at a scalding 122 to 172 degrees Fahrenheit (50 to 78 degrees Celsius). From there, the water is pumped underground through the cities’ existing district heating systems, drastically cutting down 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 US homes since its first project came online in 2024.
Carlsson thinks this model could be expanded to cities and buildings across the world—and he’s not the only one. Joint bitcoin mining and heating operations are popping up across Finland, an ideal location because of its cool climate and existing district heating systems that companies can easily plug into. Terahash Energy’s “Genesis” project, for example, is sending waste heat from bitcoin mining to be used in an industrial area in the Nordic nation, plus some nearby homes. The global bitcoin mining infrastructure firm 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. Though there’s a climate case to be made for the operation as well, Makhmetov means “sustainable” in an economic sense. That’s because Hashlabs is now insulated from a crash in the price of bitcoin—if it loses crypto revenue, it’ll still get revenue for its heating services. The heating customers are insulated, too: Hashlabs has promised to continue producing heat, even if the value of bitcoin makes its mining unprofitable.
“It was really a no-brainer in terms of: Why not do this?” said Adam Swick, MARA’s chief strategy officer. That’s because MARA gets to pull in two revenue streams: The company earns bitcoin by mining, of course, but it also earns a fee from the districts for supplying heat—all while receiving the water necessary to cool its miners for free. Each of MARA’s bitcoin heating systems are sized so they provide the minimum heat needed year-round in the cities where they operate. (In the winter, the districts use a combination of electric and biomass boilers to provide extra heat.)
Residents of the two locations where MARA operates, the region of Satakunta and the city Seinäjoki, might not realize that anything has changed, since they’re getting heat from the same pipes that they always have. “That’s kind of the goal, that nobody’s impacted,” Swick said. MARA assumed all equipment costs and is providing heat at a lower price compared to electric heating companies.
Through MARA’s eyes, it’s better for the climate, too. District heating systems in Finland are mostly powered by burning biomass, such as wood chips. While biomass is considered renewable by some, including the European Union, it still emits carbon when burned. (In the two sites where MARA installed its bitcoin miners, the districts were also burning peat.) By cutting down on the amount of biomass and peat the districts need to use, MARA calculates that it has mitigated almost 5,000 tons of greenhouse gas emissions over the 1.5 years that its districts have been operating. (To come up with this tally, the company references the latest official count of emissions caused by producing and consuming electricity in Finland to figure out how many emissions are caused by the miners, and then it compares that to the emissions stemming from traditional district heating in Finland.)
But the scheme won’t make sense for every district heating system in the Nordic nation, because many of them are already highly efficient. Nearly half source their heat from co-generation plants, or power plants that are already burning 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 heating systems from gas to low-carbon thermal energy networks. That weakens the case for heating with bitcoin.
“If a bitcoin operation is already planned, then that heat should definitely be recovered.”
And even where using waste heat from co-generation plants is not possible, reusing the heat from bitcoin mining is by no means the ideal form of efficient heating—although it is undoubtedly better than letting it go to waste. 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. That pales in comparison to the efficiency of electric heat pumps.
But while converting to heat pumps would be far more efficient, that would require costly overhauls; each individual building would have to install a heat pump and the associated infrastructure. Most existing systems are not prepared to bear these costs—another version of the dilemma Carlsson found himself confronting before he joined MARA.
When district heating systems find themselves overly reliant on imported fossil fuel sources, however, waste heat from bitcoin can offer a cost-effective solution that comes with a plausible climate case. Hashlabs got its first contract for a bitcoin heating district after Russia invaded Ukraine, sending energy prices soaring. Some district heating plants that relied on natural gas had gone bankrupt and “needed to either shut down or innovate,” said Makhmetov. 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 one thing better than efficiently using bitcoin’s waste heat is not mining bitcoin at all. Out of all forms of crypto, bitcoin consumes the most electricity—more than a small country—because of the particularly energy-intensive way it verifies transactions, which is called proof of work.
Given that most electricity grids today still run primarily on fossil fuels—unlike in Finland, which is powered by nearly 95 percent carbon-free sources, including nuclear and biomass—this could severely limit the climate case of welcoming bitcoin mining to harness its waste heat.
“It’s not a bad thing to be able to heat homes in an affordable way,” said Johanna Fornberg, a senior research specialist at the environmental advocacy nonprofit Greenpeace. “But does that actually provide justification for the industry? I would argue it does not.”
“We want to avoid believing these claims that bitcoin is providing a solution where there otherwise is not one,” she added. Greenpeace, along with other climate organizations, has advocated for bitcoin to change its verification method, which would cut its energy use drastically.
In a world where decarbonization efforts frequently involve tradeoffs, Carlsson is happy that, in this case at least, bitcoin mining produces what looks to him like a win-win.
“When I first started learning about bitcoin, I was leery of it and trying to figure out if it was a scam,” he said. Seven years later, two tiny miners sit atop 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 have to run 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 definitely be recovered and sent to a district where possible,” he said.
A reduction in energy use stemming from reuse of mining’s waste-heat “is more of a positive side-effect that largely has a negative climate impact,” said Fornberg, “not something that we want to incentivize and become increasingly reliant on in the long term.”
