In Finland's harsh winter, they keep warm by mining Bitcoin.

Author: Shaurya Malwa, CoinDesk

Translator: Chopper, Foresight News

TechFlow Guide: During the frigid winter of Northern Europe, energy-intensive Bitcoin mining is evolving into an innovative side business for capturing thermal energy. Finnish startup SunBit is attempting to convert Bitmain's liquid-cooled mining rigs into home boilers, converting nearly 100% of computational power consumption into hot water circulation at 60 degrees Celsius, using mining proceeds to directly offset heating electricity costs.

However, the economic equation of this "free heating" model is highly fragile: it faces high initial equipment costs exceeding $20,000 and is severely constrained by network-wide hash rate difficulty and electricity price fluctuations. More critically, with the 2028 block reward halving approaching, this business model can only maintain a marginal profit balance if Bitcoin's price doubles, surpassing $130,000.

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

This setup is the "Bitcoin Boiler" launched by SunBit. For every kilowatt-hour of electricity consumed by the mining rig, almost all energy is converted into heat. The device stores this heat in water, reaching temperatures up to 60 degrees Celsius, which is then circulated throughout the house via radiators and underfloor heating pipes. Operating on the same principle as oil or gas boilers, the machine continuously mines Bitcoin while running.

In simple terms, if the Bitcoin mining revenue covers the electricity bill, residents no longer need to pay continuous energy fees for heating. However, installation costs for this system exceed $20,000, and its profitability depends on Bitcoin prices, electricity rates, and network-wide hash rate competition.

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

This model also faces an unavoidable timeline. Bitcoin is expected to undergo its next halving in the spring of 2028, cutting block rewards in half. Many households may not have yet recouped their equipment costs before the halving occurs, which would directly impact this "mining-based heating" business model.

SunBit delivered its first batch of mass-produced Bitcoin boilers in 2025, with 30 systems currently in operation, CEO Elmeri Suomi told CoinDesk in an interview. Aside from one located overseas, all others are in Finland, already being used to replace or reduce the usage of gas, oil, firewood, and municipal central heating.

In 2025, they launched their first overseas project in Lelystad, Netherlands, replacing gas heating with mining rigs. In Kotka, a coastal port city in southeastern Finland with a population of around 50,000, a 200-square-meter residence combines mining rigs with existing oil boilers to form a hybrid heating system.

Image: A SunBit unit installed in a Finnish household

In an old estate in Tampere, Finland's third-largest city, mining rigs replaced wood burning, maintaining a 1,500-liter water tank between 50°C and 60°C. In Vimpeli, a similar heating system operates within a 3,000-square-meter industrial facility, equipped with an air-source heat pump that also absorbs excess power from a 30-kilowatt solar panel array.

Finland has become a testing ground for utilizing mining waste heat for district heating. Domestic company MARA also collects exhaust heat from mining rigs and connects it to the municipal heating grid to warm local residents.

This SunBit solution caters more to ordinary consumers: homeowners purchase the mining rigs themselves, replace their existing boilers, own the equipment, pay their own electricity bills, and keep all mined Bitcoin. Due to the loud noise of mining rigs, they are typically installed in basements or separate soundproof rooms.

The Profit Math of a Single Mining Rig

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

SunBit's calculation model uses Bitmain's liquid-cooled miner, the Antminer S21 XP Hydro, with a hash rate of 495T, running on third-party firmware Braiins OS. The device runs continuously 24/7, consuming approximately 5.3 kilowatts of power and drawing about 46,400 kWh annually. At an electricity rate of 11 cents per kWh, annual electricity costs amount to roughly $5,200.

Assuming a Bitcoin price of $82,000 and a network hash rate of 1040 EH/s, a single rig would mine approximately 1/12 of a Bitcoin per year. After deducting SunBit's 10% service fee, the homeowner receives Bitcoin valued at roughly $6,100; the mining pool additionally charges a 0.5% fee.

This service fee is optional and includes 24/7 remote monitoring, automatic strategy optimization aligned with Finland's floating electricity prices, a companion mobile app, and future grid peak-shaving capabilities. Without purchasing this service, homeowners receive the full 1/12 Bitcoin, valued at approximately $6,800 annually.

With the paid service, after covering electricity costs, there remains a surplus of roughly $900, making the accompanying heating effectively free. Of course, a standard residential property cannot fully utilize all the heat generated by the mining rig.

Suomi told CoinDesk, "Currently, the revenue generated per kilowatt-hour of electricity consumed in mining slightly exceeds the electricity cost, meaning heat is essentially a free byproduct." At the time of publication, Bitcoin traded at approximately $81,500. SunBit's break-even point (where mining revenue exactly equals electricity costs after service fees) sits around $70,000. This figure excludes equipment purchase costs and assumes a static network hash rate. As more rigs come online, individual earnings will decline.

Suomi shared a screenshot of a mining pool backend for an early client who purchased the 358T liquid-cooled S21+ Hydro miner. Over the past year, it mined 0.039 Bitcoin, worth approximately $3,160 at the time. This equipment can substitute for roughly 2,000 liters of heating oil annually. SunBit can only access data from initial pilot users; subsequent clients operate on independent private pool accounts, leaving the platform unable to view their metrics.

Better Than Oil Boilers, But No Match for Heat Pumps

SunBit ran a comparative breakdown for reporters: a standalone house consumes 2,300 liters of heating oil annually, at roughly $2.19 per liter, totaling approximately $5,000 in yearly fuel costs.

Switching to mining rig heating could theoretically eliminate this fuel expense. Based on the model, after deducting electricity costs, there remains an annual surplus of about $920. The complete installation package is priced at around $20,200, excluding optional add-ons. Without accounting for maintenance or loan interest, the payback period spans approximately 3.5 years. Homeowners can still retain their original oil boiler as backup during the coldest days.

However, there is a significant drawback: over half of the generated heat goes unused indoors. The included external dry cooler (a fan-equipped heatsink) vents excess heat directly outside, which is particularly pronounced in summer (late May to mid-September in southern Finland). Finland's heating season is lengthy, with winter lasting about 100 days in the southwest and up to 200 days in Lapland.

Air-source heat pumps are far stronger competitors. While a heat pump extracts heat from air or soil to produce 2.5 to 3 units of thermal energy per kilowatt-hour of electricity consumed, a mining rig converts only 1 unit of heat per kilowatt-hour.

For example: a house requires 25,000 kWh of heat annually. SunBit calculates that an air-source heat pump costs about $1,100 to run year-round, compared to roughly $3,170 for municipal central heating. If a mining rig isn't run 24/7 but only throttled down to meet exactly 25,000 kWh of heating demand, the mining revenue minus electricity costs yields an additional $490.

The trade-off is clear: heat pumps consume less electricity and offer higher heating efficiency, whereas mining rigs draw more power but allow mining profits to offset electricity bills. A rig's advantage stems entirely from crypto profitability, not thermal efficiency.

Suomi noted that mining rigs hold an edge during harsh winters: "Heat generation from rigs is unaffected by outdoor temperatures. Air-source heat pumps see efficiency plummet below -25°C, but rigs operate differently: across 365 days a year, every kilowatt-hour reliably converts into heat up to 60°C." However, a rig's operational returns are tightly bound to Bitcoin market trends and network mining difficulty, while heat pumps remain completely immune to crypto price swings. Installation costs range from $20,400 to $31,400, with estimated payback periods of 3 to 6 years.

The 2028 Halving Posits the Greatest Risk

Users placing orders for installation today will likely encounter the 2028 Bitcoin halving before recouping their investment. Block rewards will drop from 3.125 BTC to 1.5625 BTC.

SunBit's profit calculator does not account for halving impacts, calculating payback times solely based on current mining revenues. Regardless of whether Bitcoin trades at $100,000 or $20,000, the company makes no guarantees of fixed returns.

Suomi remarked: "I won't predict crypto prices or hash rate trajectories. We thoroughly explain halving history to every client, detailing how previous halvings impacted returns."

Holding original calculation parameters constant, post-halving mining revenue per kilowatt-hour would drop from 13 cents to 7 cents, falling below the 11-cent electricity rate. At that point, residents would have to pay out-of-pocket for heating, with thermal costs rising to roughly 4 cents per kWh, closely mirroring the operational expenses of comparable-efficiency air-source heat pumps.

Households installing equipment this winter will enjoy the current high-profit margin for roughly 18 more months. Applying this formula: to maintain "free heating" after the 2028 halving, Bitcoin's price must climb to approximately $131,000.

Thus, these dozens of homes in Finland have adopted a unique heating strategy: betting on continuous Bitcoin price appreciation.