Ofen 3

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.