Just a few years ago, the idea of heating your living room with a Bitcoin miner was almost a maximalist fantasy. Too noisy, too energy-intensive, too "datacenter-like," and ultimately just another geek gadget on the scene.
Today, there are companies like 21energyThis disrupts the landscape by offering a strange and fascinating machine: a designer radiator… that silently mines Bitcoin. A form of modern alchemy where the warmth of your apartment becomes the perfect excuse to accumulate sats, day after day.
This technology, long reserved for garages and warehouses, is now entering homes.
And she does it with unexpected elegance. We've been able to test this machine for a few weeks now, and it's time for us to share our first impressions.
A company born in Austria, obsessed with design and simplicity
Company 21energy is based in Tyrol, Austria. One could almost believe their products were crafted in a local artisan's workshop: thick steel painted white, aluminum, clean lines, and understated colors. The design of the heaters presented possesses an appealing minimalist elegance that blends seamlessly into the decor of a modern apartment.
Their promise can be summed up in a single sentence: to transform the inevitable heat of mining into useful and silent heating. Where traditional ASICs scream at 75 decibels, their models hover around 32 to 35 dB, creating a very low ambient noise. In other words, you forget there's a mining machine doing its job (apart from the noise, but we'll come back to that later in this article).
Since their first model, the Oven, up to their new generation Ofen 2The ambition is clear: to bring mining into European homes without compromising on comfort.
Inside the radiator: a true ASIC, optimized and domesticated
What makes these devices unique is the way they tame the heart of the problem: ASICs, machines specifically designed to calculate SHA-256 in order to mine bitcoin.
In the first generation, the Ofen included an Antminer S9, but pushed well beyond its original performance thanks to Braiins OS+, an open source firmware renowned for its autotuning capable of extracting more hash while reducing consumption.
The second generation, theOfen 2 (the one we tested) goes even further. It's no longer just a rebranded S9: the machine produces up to 40 TH/s for only 1000 watts, a ratio far above what the 16 nm chips of the old era allowed.
Inside, there are 77 carefully optimized ASIC processors, ventilated almost inaudibly, wrapped in a case designed like a designer piece.
The idea is no longer to “hide” a minor: it is to accept him, to integrate him, to make him exist in the domestic space as a discreet and useful object.
Electric heating… that reimburses part of your bill
The electricity consumed by a radiator is 100% converted into heat. This is an unavoidable law of physics. 21energy starts from this basic fact and asks a simple question: why waste this energy when it can be put to work before being dissipated?
With a conventional convector heater, you pay for each kWh of energy that provides nothing more than hot air. With a 21energy heater, that same kWh you pay for also generates Bitcoin.
So, by choosing a Often 2 radiator, you get a radiator that
- heats your apartment (for a maximum surface area of 50m2 if your accommodation is well insulated),
- generates Bitcoin at the same time.
The figures provided by the company are revealing: on an Ofen 2, the average reward is around €0,10 per kWh over one year, and can climb to €0,22 over four years, an estimate that incorporates the cyclicality of bull markets.
Over a full winter, a user can thus recover the equivalent of €200 to €300 in Bitcoin, simply by heating their home as usual.
The real secret, however, is to think long-term. Sats recovered today are sometimes worth x2, x5 or x10 once Bitcoin goes through a new bull cycle.
The patient user and the Bitcoin holder is then more broadly rewarded, if we assume that Bitcoin will continue to increase in value over time.
Profitability: not an investment, but intelligent optimization
Can we really talk about ROI when we buy a mining radiator for €1,650? Yes, but only if we understand that profitability is secondary. The goal isn't to outperform an industrial mining operation. By choosing a mining radiator, the primary objective is to replace traditional electric heating.
We already pay for electricity to heat his apartment. With a small radiator, the idea is to get part of the bill reimbursed.
Over a full winter, an Ofen 2 operating 24/24 can generate a few hundred euros worth of Bitcoin. Over several years, this silent accumulation eventually offsets a significant portion of the purchase price. The actual payback depends on:
- the price per kWh in your country,
- due to the difficulty of the network,
- of the price of Bitcoin,
- and above all… your ability to HODL.
In regions where electricity is very expensive, the logic changes: performance remains attractive, but the user has to do the math. Where 21energy becomes truly formidable and highly beneficial is for those with solar panels: instead of selling their surplus for a few cents, they can literally transform it into sats.
And at that point, the yield becomes unbeatable.
High yield for photovoltaic installations
The Ofen 2 from 21 Energy makes perfect sense when coupled with a photovoltaic installation. In a context where solar electricity is often produced in surplus during the day, this device transforms energy that is sometimes lost or undervalued into two concrete assets: useful heat and Bitcoin hashrate.
Where conventional heating would simply consume electricity, the Ofen 2 allows for the intelligent recycling of excess kilowatt-hours, thus improving the overall efficiency of the solar installation.
This synergy reduces grid dependence, smooths the profitability of photovoltaics, and gives a second economic life to the energy produced. For both individuals and professionals equipped with solar panels, the Ofen 2 is not just an innovative heating solution: it's an energy optimization tool that transforms the constraint of intermittency and surplus energy into a measurable opportunity.
A product designed for Europe, for apartments, and for patient bitcoiners.
21energy is not intended for an industrial miner. It is a European product, designed for European interiors: rooms of 20 to 50 m², long winters, well-insulated homes and inhabitants who, quite naturally, seek to reduce their bills or optimize their energy.
It's also a product for Bitcoiners. Not for speculators who want a 6-month ROI, but for those who understand the long-term dynamics of Bitcoin: accumulating slowly, patiently, mechanically.
This is the perfect embodiment of painless “stack sats”.
Limitations and drawbacks to be aware of
No product is magic. Not even when we're talking about radiators with built-in miners.
Here are some limitations to consider:
- The price may be high for some budgets. A standard radiator costs twenty times less. But it will never mine a single satoshi.
- The reward is not guaranteed: if the difficulty increases significantly and the price of BTC stagnates, the gains will decrease. That's the nature of the game, and you should be aware of this before buying.
- Finally, it's not a complete heating system: an Ofen 2 heats a living room or office very well, but it won't replace a boiler in a 200 m² chalet. However, some users might opt for several radiators in such a case.
- Even when the radiator is switched off, a slight noise can be heard. To turn it off completely, it needs to be unplugged. This can be confusing, even though a special plug would suffice to do it automatically.
Verdict: an excellent optimization tool… for an informed audience
The 21 Energy Ofen 2 is neither a simple heater nor a consumer product in the traditional sense. It is an energy and financial optimization tool, designed primarily for experienced Bitcoiners already comfortable with mining, noise management, yield volatility, and the associated technical constraints.
While it offers a rare double value (producing heat while generating hashrate), it is important to keep in mind that Bitcoin returns are neither guaranteed nor constant.
The network difficulty increases over time, which mechanically tends to reduce mining revenue, especially for home setups. Furthermore, despite careful attention to design and integration, the Ofen 2 remains an audible device, which may limit its use in certain living spaces.
However, when used in the right context (photovoltaic surplus, dedicated premises, clear understanding of the issues of the Ofen 2) it can become an excellent lever for intelligent self-consumption.
For those less experienced or sensitive to noise, there are alternatives: remote mining solutions, conventional heating coupled with Bitcoin purchased directly, or quieter but less efficient mining devices such as the Avalon nano s for example.
👉 Read: The 10 Bitcoin-powered heaters you can use in your home.
Summary table: Advantages and limitations of the 21 Energy Ofen 2
| Criterion | Evaluation |
|---|---|
| Heat generation | Excellent, useful and consistent heat |
| Valuing surplus solar energy | Very good, relevant energy optimization |
| Bitcoin Yield | Variable – depends on the network, difficulty, and price |
| Evolution of earnings over time | On the decline (structural, like any mining) |
| Sound level | Present, but not suitable for very quiet environments. |
| Effortless Access | Correct, but requires basic mining knowledge. |
| Target audience | Experienced Bitcoiners / Technical Profiles |
| An alternative for beginners | Yes, simpler and quieter solutions |
Final word: a radiator to transform a constraint into sovereignty
The 21 Energy Ofen 2 is not a miracle product, but a coherent, well-thought-out and honest tool, provided it is approached realistically.
It is aimed at those who understand that home mining is a long-term strategy, more about energy optimization than quick profits. For this specific audience, it perfectly fulfills its promise.
In a world where energy is becoming political, where heating your own apartment can sometimes become a source of anxiety, the idea of recovering part of your heating in the form of Bitcoin is almost a saving grace in a way.
For a European who heats their home several months a year, the device makes sense. For a committed Bitcoiner, it becomes almost obvious. The only real risk is trying it out… and wanting a second one.
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Read also:
- Comparison: The 10 Bitcoin heaters you can have in your home
- Heating the world with Bitcoin: when mining becomes a useful energy source
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Disclaimer This article is provided for informational purposes only and does not constitute financial or investment advice. Bitcoin mining involves risks, including those related to network volatility, changing difficulty levels, and energy costs. Some links may be affiliate links, but this will not affect the final price paid to the reader.
Heating your apartment with 21energy? We tested it for you […]