These Finland homes get free heat from bitcoin miners (as long as BTC stays above $70,000)

A 180-square-meter house in icy Nokia, a small town in Finland that gave the once-popular phone maker its name, has fully disconnected from the district heating network and now heats its rooms with a bitcoin miner.

The machine sits inside what SunBit, a Finnish company, sells as a Bitcoin Boiler. Every kilowatt-hour a mining computer draws comes out as heat. SunBit captures that heat in water at up to 60°C and pushes it through a building’s radiators and floor pipes the way an oil or gas boiler would. The boiler earns bitcoin the whole time it runs.

Essentially, the idea is that if the bitcoin earned covers the electricity consumed, the homeowner effectively gets heat without an ongoing net energy bill. But the system costs roughly $20,000 or more to install, and its profitability depends on bitcoin's price, electricity costs and the amount of computing power competing for mining rewards.

“The heating itself works regardless of the market, and only the payback time moves,” Suomi said.

There's also a deadline built into that calculation. Bitcoin's next halving, which is expected in spring 2028, will cut the amount of new bitcoin awarded to miners in half. That could happen well before homeowners recover the cost of their heating systems, potentially throwing a wrench in the pitch for the Bitcoin Boiler.

SunBit, which delivered its first production batch of Bitcoin Boilers in 2025, now has 30 systems running, founder and CEO Elmeri Suomi told CoinDesk this week. All but one are in Finland, and between them they have replaced or cut back on gas, oil, wood and district heating.

At a commercial property in Lekkum, in the Netherlands, SunBit’s first export project in 2025, a miner replaced gas heating. In Kotka, a port city of about 50,000 on Finland’s southeast coast, a 200-square-meter house runs one alongside its existing oil boiler as a hybrid system.

A bitcoin mining machine installed in a Finnish home. (Sunbit)

At an old manor house in Tampere, Finland’s third-largest city, mining replaced wood heating, and the miner keeps a 1,500-liter water tank at 50°C to 60°C. A 3,000-square-meter industrial hall in Vimpeli runs one alongside an air-to-water heat pump, and it soaks up surplus power from a 30-kilowatt solar array.

Finland is already the testbed for heating with mining. MARA’s systems feed waste heat from its miners into district heating networks in Satakunta and Seinäjoki, warming about 80,000 residents.

SunBit is bringing the concept closer to the consumer: the property owner buys the mining machines, installs them where the boiler used to be, so the household owns the machines, pays for their power and keeps the bitcoin. The machines sit in a basement or an attached room insulated for sound, since mining rigs are loud.

The math on one miner

For an owner like the one in the town of Nokia, it comes down to the power bill and whether the bitcoin covers it.

SunBit’s financial calculator assumes one machine, a 495-terahash variant of Bitmain’s water-cooled Antminer S21 XP Hydro running Braiins OS, third-party firmware SunBit uses to tune its miners. Running nonstop at about 5.3 kilowatts, it uses roughly 46,400 kilowatt-hours a year.

At about 11 cents per kilowatt-hour, that power costs roughly $5,200 a year (this converts SunBit's original figures, from euros at Sunday’s rate of about $1.11).

SunBit assumes bitcoin at about $82,000 and the network’s total computing power at 1,040 exahashes per second.

Under those assumptions, the company estimates the miner would mine about one-twelfth of a bitcoin a year. After SunBit’s 10% service fee, the owner keeps about $6,100 worth. Mining pool fees take about 0.5% more on top, Suomi said.

The fee is optional. It pays for SunBit’s remote-control service, which covers 24/7 monitoring, optimization around Finland’s spot power market and a phone app, with grid balancing planned. An owner who skips the service keeps the full twelfth of a bitcoin, about $6,800 a year, according to Suomi.

With the service, the owner could see a surplus of roughly $900 over the modeled electricity bill, before paying for the system itself. The heat costs nothing extra on top of that, though a typical house can’t use all of it, as shown below.

“Mining currently earns slightly more per kWh than the electricity costs, so the heat is essentially a free by-product,” Suomi told CoinDesk.

Bitcoin traded near $81,500 as of U.S. morning hours Friday, CoinDesk data shows. SunBit puts the owner’s break-even, the price at which mining income after its fee just covers the power bill, at just under $70,000, roughly 15% lower. That figure leaves out what the system cost to buy.

The calculator also holds the network’s computing power fixed at today’s level. If more machines join the network, each one earns less.

One of SunBit’s first customers, who bought a cheaper 358-terahash Antminer S21+ Hydro, has mined about 0.039 bitcoin over the past year, worth roughly $3,160 at current prices, according to a screenshot of the customer’s mining pool account that Suomi shared with CoinDesk. That system replaced about 2,000 liters of heating oil a year. SunBit can see pool data only for its first pilot customers, Suomi said, since subsequent customers get their own private accounts.

Oil is easy to beat. Heat pumps aren’t

In a worked example SunBit gave CoinDesk, a detached house burns 2,300 liters of heating oil a year at about $2.19 a liter, a bill of roughly $5,000.

Replacing that oil consumption with a miner could theoretically eliminate the fuel bill and, under SunBit's current assumptions, may generate about $920 in mining income after electricity costs, roughly $6,000 a year against SunBit’s quoted installed price of about $20,200, which Suomi said covers the basic system with no extra costs.

That puts payback at about three and a half years before maintenance or financing, and the old oil boiler can stay for the coldest days, the company's calculation showed.

There’s a catch, however.

More than half of that heat never reaches the house. A dry cooler outside, essentially a radiator with fans, dumps whatever the house can’t use into the Finnish air, most of it in summer, which in southern Finland runs from late May to mid-September, according to the Finnish Meteorological Institute. The rest of the year is heating season, and the deep winter alone lasts about 100 days in the southwest and 200 in Lapland.

Heat pumps are a tougher rival, however. They pull warmth from outside air or the ground and deliver 2.5 to 3 kilowatt-hours of heat for every kilowatt-hour of electricity, while a miner turns each kilowatt-hour into exactly one.

For a house using 25,000 kilowatt-hours of heat a year, SunBit puts an air-to-water heat pump’s running cost at about $1,100 and district heating at about $3,170. Run only long enough to cover that house’s 25,000 kilowatt-hours, rather than nonstop, the miner instead earns about $490 more than its electricity costs.

This shows the trade-off: a heat pump requires much less electricity to deliver the same amount of heat, whereas a bitcoin miner consumes more electricity but can generate revenue that offsets its operating costs. The miner's apparent advantage depends on mining profitability rather than superior heating efficiency.

Suomi says winter is where a miner pulls ahead. “A miner’s output does not depend on outdoor temperature. Unlike an air-source heat pump, its efficiency does not drop at –25 °C: 100% of the electricity becomes heat at up to 60 °C, every hour of the year,” he said.

A miner’s running cost, though, also hangs on bitcoin’s price and how much computing power competes for each block.

“The trade-off is that the economics depend on Bitcoin price and network difficulty, which a heat pump doesn’t,” Suomi said, putting payback at three to six years for systems that cost about $20,400 to $31,400 installed.

The 2028 halving

Anyone who buys a system now will hit bitcoin’s next halving in 2028 before it pays for itself. The event is scheduled to halve the new coins awarded for each block from 3.125 to 1.5625 bitcoin.

SunBit’s calculator leaves it out. It prices payback based on today’s profitability, whether bitcoin trades at $100,000 or $20,000, because the company can’t guarantee income.

“I personally don’t want to give price predictions and difficulty predictions,” Suomi said, adding that SunBit explains the halving to every customer instead, using its past effect on profitability.

Holding SunBit’s own inputs fixed, mining income would drop from about 13 cents per kilowatt-hour to about 7 cents, below the 11-cent power price. The heat would then cost the owner about 4 cents per kilowatt-hour, close to what an air-to-water heat pump costs to run at SunBit’s assumed efficiency. A household that installs this winter gets roughly 18 months at today’s margins before the cut.

On that math, a miner-heated house in Finland keeps its free heat after 2028 halving only if bitcoin trades above roughly $131,000, about 60% above Friday’s price. So, for a few dozen buildings in Finland, the 'number go up' is now a heating plan.