Article by Shaurya Malwa, CoinDesk

Translated by Chopper, Foresight News

DeepChaohao Summary: In the frigid Nordic winters, energy-intensive Bitcoin mining is evolving into an innovative side hustle for heat recovery. Finnish startup SunBit is retrofitting Bitmain’s water-cooled miners into home boilers, converting nearly 100% of computational power into 60°C heating water, directly offsetting heating electricity costs with mining revenues.

However, this "free heating" economic model is highly fragile: it not only requires a substantial initial equipment investment of over $20,000 but is also severely constrained by network hash rate difficulty and electricity price volatility. More critically, with the upcoming 2028 Bitcoin block reward halving, this business model can only maintain marginal profitability if Bitcoin’s price doubles to surpass $130,000.

In the town of Nokia, Finland, a 180-square-meter house has completely disconnected from the regional district heating system and now relies entirely on Bitcoin mining machines for heating.

This equipment is SunBit’s “Bitcoin Boiler.” For every kilowatt-hour of electricity consumed, the miner converts nearly all of that energy into heat. The device stores this heat in water, raising the temperature up to 60°C, and then distributes it throughout the home via radiators or underfloor heating pipes—just like a traditional oil or gas boiler—while simultaneously mining Bitcoin.

In simple terms, if the Bitcoin mining revenue covers the electricity cost, residents effectively get heating without continuously paying for energy. However, the system’s installation cost exceeds $20,000, and profitability depends on Bitcoin’s price, electricity rates, and the overall network mining difficulty.

SunBit founder Suomi said: "The heating function itself is unaffected by market conditions; only the payback period changes."

This model also has an unavoidable timeline: Bitcoin is expected to undergo its next halving in spring 2028, cutting the block reward in half. Many users may not yet have recouped their equipment costs when the halving occurs, directly impacting the viability of this "mining-for-heating" business model.

SunBit delivered its first batch of mass-produced Bitcoin boilers in 2025, and currently, 30 systems are operational, CEO Elmeri Suomi told CoinDesk in an interview. All but one of the systems are located in Finland, where they have been used to replace or reduce reliance on natural gas, oil, wood, and municipal district heating.

In 2025, they launched their first overseas project in Leekum, the Netherlands, replacing gas heating with mining equipment. In Kotka, a port city on the southeastern coast of Finland with a population of approximately 50,000, a 200-square-meter residential building integrates mining equipment with an existing oil-fired boiler to form a hybrid heating system.

Image: A SunBit device installed in a home in Finland

In an old manor in Tampere, Finland’s third-largest city, mining equipment has replaced wood-burning stoves to maintain a 1,500-liter water tank at a temperature between 50°C and 60°C. A similar heating system operates in a 3,000-square-meter industrial facility in Vimpeli, equipped with an air-source heat pump and also absorbing excess electricity from a 30-kilowatt solar panel array.

Finland has become a testing ground for using mining waste heat for heating. The local company MARA also captures the waste heat from mining equipment and feeds it into the municipal heating network to warm local residents.

The SunBit solution is designed for everyday consumers: homeowners purchase their own mining equipment and replace their existing boiler, with the device belonging to the homeowner, electricity costs paid by the homeowner, and all mined Bitcoin retained by the homeowner. Due to the high noise level of the mining equipment, it is typically installed in a basement or a dedicated soundproof room.

A mining rig's earnings statement

Taking the homeowner in Nokia Town as an example, the core issue is a simple income-versus-expense comparison: whether mining revenue can cover the electricity costs.

SunBit’s calculation model uses the Bitmain water-cooled mining rig, the Antminer S21 XP Hydro, with a hash rate of 495 TH/s and running on third-party firmware Braiins OS. The device operates continuously 24/7, consuming approximately 5.3 kW of power and about 46,400 kWh of electricity per year. At an electricity rate of $0.11 per kWh, the annual electricity cost is approximately $5,200.

Assuming a Bitcoin price of $82,000 and a global hash rate of 1,040 EH/s, under these conditions, a single mining machine can mine approximately 1/12 of a Bitcoin per year. After deducting SunBit’s 10% service fee, the owner receives Bitcoin worth approximately $6,100; additionally, the mining pool deducts a 0.5% handling fee.

This service fee is optional and includes 24/7 remote monitoring, automated optimization strategies aligned with Finland’s variable electricity prices, a companion mobile app, and upcoming grid peak-shaving functionality. Without purchasing this service, owners receive the full 1/12 of a Bitcoin annually, worth approximately $6,800.

With a paid service, you can still save approximately $900 after deducting electricity costs, and the accompanying heating is essentially free. Of course, a typical residential home cannot fully utilize all the heat generated by the mining equipment.

Suomi told CoinDesk, “Currently, the revenue generated per kilowatt-hour of electricity consumed in mining is slightly higher than the electricity price, so heat is essentially a free byproduct.” At the time of the report, the price of Bitcoin was approximately $81,500. SunBit’s break-even point—after deducting service fees, where mining revenue exactly equals electricity costs—is around $70,000. This figure does not include the cost of purchasing the mining equipment itself and assumes constant network hash rate. If more mining machines come online, the revenue per machine will decrease.

Finland provided a screenshot of the mining pool dashboard from an early customer who purchased a S21+ Hydro water-cooled miner with 358 TH/s hashrate. Over the past year, the device mined 0.039 BTC, worth approximately $3,160 at the prevailing market price. This equipment can replace about 2,000 liters of heating oil annually. SunBit can only access data from the initial pilot users; subsequent customers use independent private mining pool accounts, so their data is not visible on the platform.

Better than oil boilers, but can't beat heat pumps.

SunBit calculated a comparison for journalists: a single-family home consumes 2,300 liters of heating oil annually, at a price of approximately $2.19 per liter, resulting in annual fuel costs of about $5,000.

Switching to mining rig heating could theoretically eliminate this fuel expense. According to the model, after deducting electricity costs, you could still achieve an annual surplus of approximately $920. The total equipment installation quote is around $20,200, excluding additional upgrades. Without accounting for maintenance or loan interest, the payback period is approximately 3.5 years. The original oil-fired boiler can still be retained as a backup during the coldest days.

However, there is a drawback: more than half of the generated heat is unusable. The external air-cooled radiator (a fan-equipped cooling unit) that comes with the equipment directly vents the excess heat outdoors, especially noticeable in summer (late May to mid-September in southern Finland). Finland has a long heating season, with winter lasting approximately 100 days in the southwest and up to 200 days in Lapland.

Air-source heat pumps are the stronger competitors. For every 1 kWh of electricity consumed, heat pumps can transfer heat from the air or soil to produce 2.5 to 3 kWh of thermal energy; whereas mining rigs can only convert 1 kWh of electricity into 1 kWh of heat.

For example, a house requires 25,000 kWh of heat per year. SunBit calculates that the annual operating cost of an air-source heat pump is approximately $1,100, while municipal district heating costs about $3,170. If the mining rig does not run continuously throughout the year but operates only enough to meet the 25,000 kWh heating demand, the mining revenue minus electricity costs would still yield an additional profit of $490.

The trade-off is clear: heat pumps use less electricity and offer higher heating efficiency; miners consume more power, but mining rewards can offset electricity costs. The advantage of miners comes entirely from mining profitability, not from heating efficiency itself.

Finland suggests that mining rigs have an advantage in winter: "The heat output of mining rigs is unaffected by outdoor temperatures. While air-source heat pumps experience a sharp drop in efficiency at temperatures as low as -25°C, mining rigs are different: every kilowatt-hour of electricity is consistently converted into heat up to 60°C, 365 days a year." However, the profitability of mining rigs is tightly tied to Bitcoin’s price and the network’s mining difficulty, whereas heat pumps are completely unaffected by cryptocurrency prices. The total installation cost for the entire system ranges from $20,400 to $31,400, with an estimated payback period of 3 to 6 years.

The 2028 halving is the greatest risk.

Users who place an order and install now will most likely encounter the 2028 Bitcoin halving before recouping their investment. The block reward will decrease from 3.125 BTC per block to 1.5625 BTC.

SunBit's return calculator does not account for the impact of halving; it estimates payback time based solely on current mining rewards. Regardless of whether the coin price is $100,000 or $20,000, the company does not guarantee fixed returns.

Suomi said: "I won't try to predict coin prices or hash rate trends. We clearly explain the history of halvings to every client and inform them about the impact halvings have had on returns in the past."

Under the same original calculation conditions, after the halving, the mining revenue per kilowatt-hour will decrease from 13 cents to 7 cents, below the electricity price of 11 cents. At this point, heating costs must be borne independently, with each kilowatt-hour of heat costing approximately 4 cents—close to the operating cost of an equally efficient air-source heat pump.

Households installing equipment this winter have approximately 18 months left to enjoy the current high profit margins. According to this formula, for "free heating" to continue after the 2028 halving, the price of Bitcoin would need to rise to approximately $131,000.

Thus, these dozens of houses in Finland have a unique heating solution: betting on Bitcoin’s continued price increase.