Frequently asked questions

We typically ship all products within 2-3 business days. Following that, your order will reach you within a few business days, depending on the delivery location. Any pre-orders or delays will be indicated in the description or in a separate message.

Currently, we ship to the EU, Switzerland, Norway and Great Britain. If you want to find out if we deliver to your address, you can easily test this in the checkout process by entering your address there.

The shipping costs vary depending on the delivery location. To calculate your personal shipping costs, you can go through the checkout process. After entering the delivery address, the costs will be displayed to you. All orders over €200 qualify for free shipping!

For all customers within the EU, there are no additional costs due to taxes and customs. All customers outside the EU pay only the net price in the store when ordering. Therefore, taxes and duties will be incurred upon import and are to be paid there.

Yes, every customer has a 30-day right of withdrawal. Within this period, you can cancel your order without providing any reasons. The paid amount will be refunded to you via the originally selected payment method.

No, these products do not require more electricity than traditional heaters. They efficiently convert 100% of the electrical energy into heat, simultaneously utilizing it to mine Bitcoin, effectively leveraging energy in a dual capacity.

If the same heating method (electric heating) with the same heat demand is applied as before, the electricity bill usually does not change, as the entire electrical energy continues to be converted into heat.

All our devices offer several heat levels you can choose from.

The heating area of each heater is specified in the product descriptions, which may vary significantly depending on their characteristics. For all individual hardware devices, the heating area can be determined using various calculators available online, based on the specified power output.

Our heaters are only allowed to be operated at the maximum power specified in the description and/or user manual. Overclocking poses a high risk and will void the warranty immediately. Similarly, each individual Bitcoin mining device should only be operated at its maximum standard power.

Bitmain specifies a coolant inlet temperature of 20 to 40 °C for the S19 XP+ Hyd.

Treat 40 °C as your operating ceiling and leave yourself some headroom. A miner running right at its limit will shut down as soon as anything in the loop is slightly off, for example a hot day, reduced flow or a heat exchanger that needs cleaning.

Never run the miner without a filled, connected cooling loop.

The permitted range differs between models, so check the datasheet for the machine you actually have before you set your loop temperature.

All of our heaters and miners are CE compliant. They have been tested against the relevant European safety standards.

Yes. Our devices run an operating system that constantly monitors the temperature and shuts the device down once it reaches the defined limit. This protection can only do its job when the device is operated within its specification. The airflow must not be blocked and the dust filter has to be kept clean, as described in the user manual. The protection also needs the firmware that we install at the factory. Third party firmware or changed temperature settings can switch it off.

We give a voluntary manufacturer's guarantee of 12 months from the date of purchase. It covers faults in material and workmanship, as long as the device was installed and operated according to the user manual. This applies to our heaters and to the Bitcoin miners we sell, both new and refurbished. This voluntary guarantee is in addition to your statutory consumer rights and does not limit them.

Please contact our support first and we will arrange the next steps with you. When you send a device back, please use its original packaging so it is protected during transport.

Please run your device at the default power that is stated in the product description or in the user manual. Running it above its factory default settings, for example by raising the clock speed or voltage to get more power, is called overclocking and is operation outside the specification. This puts heavy stress on the hardware and can damage it for good. You should also never turn off the protective functions. If overclocking causes a defect, the principle described above applies.

We strongly advise against installing different or custom firmware. The device is set up to run on the firmware that we install before delivery, and that is how it is meant to be used. Custom firmware is mostly used to overclock or to change voltage and temperature settings, which takes the device outside its specification and can damage it. If you still choose to install it, you do so at your own risk. Custom firmware voids the voluntary manufacturer's guarantee, and any damage it causes does not count as a product defect. Faults that have nothing to do with the firmware change are not affected.

Please do not open the device or change its hardware. Opening the device or changing any of its parts takes it away from the condition it was delivered in, and the same goes for repairs you carry out yourself. If something is wrong, please contact our support first and we will find the best solution together with you. If an unauthorized change or repair causes a defect, the principle described above applies.

You will find the allowed temperature and humidity for your device in its user manual. Please keep the device within these conditions at all times so that it runs safely and reliably.

Miners and heaters are sensitive to an unstable supply and to incorrect fusing. Please make sure the power supply is stable and correctly fused, and that it is connected the way the user manual describes, so that your device is protected against problems coming from the grid.

No. A hydro cooled miner may only run inside a closed cooling loop that is properly filled. If you start it without a connected cooling system, it can be damaged beyond repair within a very short time. Always check that the cooling loop is connected and filled before you start the device.

Use only the coolant that the manufacturer recommends and keep the water temperature, the flow rate and the pressure within the limits given in the manual. A good choice is deionized or distilled water with a corrosion inhibitor and a biocide. You can also use a ready mixed non conductive coolant. Please follow the pH value that the manufacturer specifies. Tap water or running the system outside the specified values can damage the device.

Air cooled devices are not made for immersion cooling. Converting one so that it can be submerged in fluid is technically demanding, and even a small mistake with the fluid or the conversion can cause a short circuit and damage the device beyond repair. A conversion like this is operation outside the specification, and the principle described above applies to any damage that results from it. If you want to run immersion, please talk to us first, because there are devices that are built for it.

21energy heaters and computers (mining devices) generate revenue through the process of Bitcoin mining, wherein specialized hardware solves cryptographic puzzles to validate and secure transactions on the blockchain network. As a reward for their computational work, miners receive newly minted bitcoins and transaction fees.

Your mining earnings depend on various factors such as the price of Bitcoin, market rates for computations, global hashing power, duration of operation, and hardware model. For your individual situation, we have developed a profitability calculator. The significant distinction from any other electric heater is that cash flow is generated while heating.

Please feel free to submit an inquiry through our contact form on the website. Please provide all necessary information so that we can process your request as efficiently as possible.

Yes, we have specific pricing tiers for certain products starting from a certain quantity. Please feel free to send us an inquiry through our contact form for more information.

Please feel free to email us at office@21energy.com and we will get back to you.

Please have a look at our open positions.

No, we do not offer hosting.

We sell the hardware, and we support you in running it at your own location.

There are two housings and four models.

• Ofen 3 Base: about 1 kW, rooms up to 50 m²
• Ofen 3 Pro: about 1 kW, rooms up to 55 m²
• Ofen 3 Base XL: about 2 kW, rooms up to 100 m²
• Ofen 3 Pro XL: about 2 kW, rooms up to 110 m²

As a rule of thumb: if a single radiator already keeps the room comfortable, a 1 kW model is enough.

Same heat, more mining. Both put out about 1 kW in the same housing, so they warm the same room.

The difference is the mining hardware inside: 40 TH/s in the Base, 60 TH/s in the Pro. The Pro earns roughly 50% more from every kilowatt hour it uses, so more of your electricity bill comes back each winter.

The two large models pair up the same way: 80 TH/s in the Ofen 3 Base XL, 120 TH/s in the Ofen 3 Pro XL, both at about 2 kW.

The mining runs whenever the heater runs, and the Bitcoin it earns pays back part of the electricity you used.

The Base models return around €0.10 per kilowatt hour consumed, the Pro models around €0.13, both measured at the four year Bitcoin average as of August 2026. What that is worth to you depends on your own tariff: at €0.25 per kWh a Pro covers roughly half of the power it draws.

See what that looks like at your own electricity price in our profitability calculator. Mining income moves with the Bitcoin price and with network difficulty, so treat every figure as an estimate rather than a fixed payout.

No. Every electric heater turns the electricity it draws into heat, so a 1 kW Ofen 3 uses exactly as much power as any 1 kW electric radiator at the same setting.

What is different is what comes back: the Ofen 3 mines while it heats, and that income pays part of the same bill.

If you heat with oil, gas or a heat pump today, the comparison depends on your own tariff and on your fuel price.

Yes, that is exactly what it was designed for. The Ofen 3 Base and the Ofen 3 Pro run at about 35 dB, quieter than a fridge. The two XL models sit at about 40 dB.

With the 21energy app, on iOS and Android. Setup takes about three minutes: you connect the heater to your Wi-Fi and the app handles the rest. After that you switch it on and off, set the heat level, and see what it has mined. Every 21energy heater lives in the same app, so a second one just shows up alongside the first.

Yes, and it does the device no harm. Schedules are built into the 21energy app: you set the on and off times and the heat level for each.

One thing worth knowing: the firmware needs a short warm-up after every restart before it reaches full efficiency, so a lot of very short cycles will cost you a little hashrate.

Yes. The Ofen series has an official Home Assistant integration. Any other smart home system can connect through the open API on the device, and you find the interface specification in the 21energy app under Automations.

The Ofen 3 needs very little bandwidth, under 1 Mbit/s. What matters far more is that the connection is stable, since the heater stays connected to a mining pool the whole time it is on.

The Bitcoin the Ofen 3 mines is credited to your mining pool account first. From there you decide where it goes: to your own Bitcoin wallet if you want to hold it yourself, or straight to an exchange to be paid out in euros. You only need a wallet for the first route. The app walks you through the setup, and the user manual covers it in detail.

You get a voluntary manufacturer's guarantee of 12 months from the date of purchase, on top of your statutory consumer rights and without limiting them. It covers faults in material and workmanship as long as the heater was installed and operated according to the user manual.

It is built to run unattended through a heating season. The Ofen 3 is CE compliant and tested against the relevant European safety standards, and its operating system watches the temperature continuously and shuts the device down before it reaches the defined limit.

For that protection to do its job, keep the airflow clear, keep the dust filter clean and leave the factory firmware in place.

Yes, there is a USB port on the back of the Ofen 2, through which you can connect a LAN cable using a suitable adapter.

The Ofen 2 can be controlled via the 21energy App. You can turn it on and off, adjust the heating levels, connect it to a thermostat, create schedules, and integrate it into your Home Assistant setup.

A Bitcoin wallet is required if you want to store the earnings from your mining pool yourself. Alternatively, you can send the earnings directly to an exchange and have them paid out in euros.

The Bitcoins mined by the Ofen 2 are first credited to your mining pool account. From there, you can transfer them to your Bitcoin wallet or directly to an exchange. More details can be found in theuser manual, section 5.4.

The Ofen 2 requires very little bandwidth (<1 Mbit/s). The most important factor is that the connection is stable and reliable.

This is not recommended by default and should only be done if the Ofen 2 is placed and secured carefully and safely. The wall mount is designed only for horizontal installation.

Yes, there is a USB port on the back of the Ofen 2 Pro, through which you can connect a LAN cable using a suitable adapter.

The Ofen 2 Pro can be controlled via the 21energy App. You can turn it on and off, adjust the heating levels, connect it to a thermostat, create schedules, and integrate it into your Home Assistant setup.

A Bitcoin wallet is required if you want to store the earnings from your mining pool yourself. Alternatively, you can send the earnings directly to an exchange and have them paid out in euros.

The Bitcoins mined by the Ofen 2 Pro are first credited to your mining pool account. From there, you can transfer them to your Bitcoin wallet or directly to an exchange. More details can be found in theuser manual, section 5.4.

The Ofen 2 Pro requires very little bandwidth (<1 Mbit/s). The most important factor is that the connection is stable and reliable.

This is not recommended by default and should only be done if the Ofen 2 Pro is placed and secured carefully and safely. The wall mount is designed only for horizontal installation.

Yes. The Ofen 2, Ofen 2 Pro and Port are all controlled through the 21energy App. For Home Assistant there is an official integration. Every other system can control the device through its open API. You will find the full interface specification in the app under "Automations".

Yes. Occasional on/off cycles don't harm the hardware.

The 21energy Port is a small controller that sits between your network and your miners. With it, this is all built in: switching miners on and off, changing power levels, setting time schedules, all from the 21energy app. Coupling the miner to your solar system runs through our Home Assistant integration.

On miners running Braiins OS, the autotuning firmware needs a short warm-up after each restart before it reaches full efficiency, so very frequent cycles cost a bit of hashrate. Never run a water-cooled miner without a filled and connected cooling loop.

Yes, via the 21energy Port. It works with all Bitmain Antminer devices that have Braiins OS installed. You connect your miner to the Port, and the Port connects to Home Assistant through our official integration. The miner then appears as a normal device: switch it on and off, change power levels, build it into your own automations, for example together with your solar system.

If you run a different smart home system, you don't need Home Assistant. The Port has its own local REST API, so any system that can send HTTP requests can control it directly, for example Loxone, ioBroker, openHAB or Node-RED. Only the effort differs: with Home Assistant the integration is ready to install, otherwise you build the automation yourself. Get in touch if you want to go that route and we'll send you the API documentation.

For a standalone ASIC miner running Braiins OS, control works through the public Braiins OS gRPC API. There is no finished integration, so you write the automation yourself. It works, it just takes more setup than the Port.

Work through this in order.

1. Check the LEDs on the miner’s LAN socket. Green and yellow should be lit or blinking. No LEDs means there is no physical link at all.
2. Swap the network cable, then try a different port on your switch or router.
3. Make sure the miner sits on the same network segment as your computer. No guest Wi-Fi, no separate VLAN, no client isolation on the router.
4. Scan your network for the device. Braiins Toolbox finds miners running Braiins OS. Otherwise use a scanner like Angry IP Scanner or Advanced IP Scanner, and look for a device named "miner".
5. On Antminers with stock firmware you can also use Bitmain’s IP Reporter tool. Hold the IP Report button on the control panel until it beeps and the IP appears on your screen.
6. If a static IP was set earlier and nobody knows it, or it clashes with another device: power the miner on, let it run for five minutes, then hold the reset button for ten seconds. That restores factory settings, including DHCP.
7. If it still does not appear, reboot your router and check that DHCP is switched on and has not run out of addresses.

Still nothing after all that? Contact our support with your device model and what you have already tried.

For a standalone miner, send us two things: screenshots of the web interface and the log archive you can export from the firmware. Together these usually pin down the issue.

We can't log into a standalone miner directly. On 21energy devices such as our Ofen and the Port it is technically possible, since they connect through the 21energy app.

A hydro-cooled ASIC miner is connected to your central storage tank instead of an oil or gas burner. It runs Bitcoin computations and turns nearly 100% of the electricity into heat, warming the water that feeds your radiators, underfloor heating and hot water, while the computing earns you Bitcoin.

Both. With around 7 kW of output and outlet temperatures of 70 °C and above, it can be the primary heat source for a single-family home. You can also run it as a smart add-on alongside an existing heat pump, gas or oil boiler.

Yes. It's retrofittable, it connects to standard storage tanks and water-based heating circuits and works with both radiators and underfloor heating. There's no need to replace what already works.

About the same as any electric heater: near 100% of the electricity becomes usable heat. The difference is that this one also earns, part of your heating bill comes back to you as Bitcoin Cashback, paid out daily and fully transparent.

No, it works on any electricity supply. If you do have solar, you can mine with your PV surplus instead of feeding it into the grid, for up to 5× the return of a standard feed-in tariff.

It's engineered and made in Austria and launches in Q4 2026. Join the waitlist to be first in line and get notified the moment it's available.

An ASIC miner (also called a BTC miner or crypto miner) is hardware built for a single job: mining Bitcoin using the SHA-256 algorithm. Unlike a PC or graphics card, an ASIC (Application-Specific Integrated Circuit) does only this, but does it extremely efficiently. Efficiency is measured in joules per terahash (J/TH): the lower the number, the less electricity each unit of mining work costs.

No. All our miners ship from our warehouse in Austria. Customers inside the EU (including Germany, Austria, France, Finland, Sweden, and more) pay no customs or import duties. The shop price is the final price.

Customers outside the EU will pay country-specific import duties on delivery, we only display the net price for such orders.

In-stock miners typically arrive within 2–3 business days across the DACH region.

For pre-orders or custom configurations, the expected lead time is stated directly on the product page. All orders over €200 inside the EU qualify for free shipping.

All new, originally packaged ASIC miners we sell come with a 12-month warranty, provided the operating conditions (ambient temperature, power supply, no overclocking) are observed.

Repairs or replacements are handled directly through our European support, no return to China or the US required.

Technically, every ASIC miner converts ~100% of its electricity into heat, that is the physical reality. For residential heating use, we recommend our Ofen 2 series: insulated housing, quiet operation, designed as furniture, and a control app.

Plain ASIC miners (e.g. Antminer S21) can also be used as a heat source for basements, offices, or workshops, but they are louder and less living-room friendly.

We accept SEPA transfer, credit and debit cards (Visa, Mastercard), Apple Pay, Google Pay, and Klarna (pay-over-time).

For B2B orders and larger quantities, we offer custom payment terms, contact our business team for details.

Yes to all three. We sell the Bitaxe 603 Gamma at 1.54 TH/s, the Bitaxe 602 Gamma Premium at 1.3 TH/s, plus the Nerdaxe Gamma Premium at 1.3 TH/s and around 19.5 W.

They ship from our warehouse in Austria, so there is no customs hassle inside the EU. You get a 12 month warranty, support runs through our European team, and nothing has to go back to China or the US.

We are happy to help you get it set up.

Between 900 and 2,760 watts. At stock it runs 2,415 to 2,760 W; with Braiins OS you can underclock it to as low as 900 W to cut power use.

Loud at full speed, comparable to a vacuum cleaner. The S19 Silent Kit brings it down to as low as 50 dB (at reduced performance), and underclocking with Braiins OS helps too.

Yes. It needs a 200 to 240 V circuit and an Ethernet connection. Plan for noise and heat (2 to 2.8 kW), so a garage or utility room works well, or the S19 Silent Kit for living spaces.

Up to 18 J/TH with Braiins OS, about 23 J/TH on stock Bitmain firmware.

Braiins OS for most home miners: better efficiency (down to 18 J/TH), autotuning, and adjustable power from 900 W. Stock Bitmain OS is simpler but less efficient and not tunable that low.

Refurbished for the best price per terahash (fully tested); new for maximum remaining lifespan. Both come in 105, 110, 115, and 120 TH.

It needs 200 to 240 V (not 110 to 120 V) via a C19/C20 cable. A dedicated 230 V circuit is fine in Europe; in North America use a 240 V circuit.

It depends on your electricity price, the Bitcoin price, and network difficulty. Estimate your own numbers with our profitability calculator.