BitcoinOverview
The 21energy Ofen 3 Base XL is an electric room heater that mines Bitcoin while it heats. Inside, 80 TH/s of SHA-256 mining chips act as the heating element: every one of the 2.0 kW it draws comes out as heat, exactly as it would from a conventional electric panel heater, but the chips earn Bitcoin at the same time. It is sized for rooms up to 100 m², runs at 40 dB and plugs into a normal household socket.
The Ofen 3 is 21energy's 2026 heater generation and replaces the Ofen 2. It comes in four models across two housings: the slim Base (40 TH/s) and Pro (60 TH/s), and the larger Base XL (80 TH/s) and Pro XL (120 TH/s). The Pro models use more efficient chips (17.5 J/TH against 20 J/TH), which is why they mine about 50% more for almost the same heat output.
Key Features
- 2.0 kW heat output – heats rooms up to 100 m²
- 80 TH/s Bitcoin mining at 20 J/TH chip efficiency
- 40 dB – quiet enough for a living room or home office
- Plug in and go: standard socket, set up over Wi-Fi in about three minutes with the 21energy app (iOS and Android)
- App control: switch on and off, set the heat level and see what it has mined
- Your pool, your wallet: mined Bitcoin is credited to your mining pool account and paid out to a wallet or exchange you choose
- Two finishes: white or black
Technical Specifications
| Manufacturer | 21energy (Austria) |
| Model | Ofen 3 Base XL |
| Type | Bitcoin mining heater |
| Algorithm / Coin | SHA-256 / Bitcoin (BTC) |
| Hashrate | 80 TH/s |
| Heat output / power draw | 2.0 kW |
| Chip efficiency | 20 J/TH |
| Room size | up to 100 m² |
| Noise | 40 dB |
| Dimensions | 63 × 83 × 16 cm |
| Connectivity | Wi-Fi (WLAN), 21energy app |
| Power | Standard household socket |
| Manufacturer guarantee | 12 months, on top of statutory EU rights |
| Condition | Brand new |
Mining Profitability
A Bitcoin heater is not judged like a data-centre miner. You are paying for the heat either way, so the question is how much of the electricity bill the mining gives back.
| At today's numbers | Ofen 3 Base XL |
|---|---|
| Mining revenue per day | $3.27 |
| Electricity per day (48.0 kWh at the EU household average of €0.2896/kWh) | $15.85 |
| Share of the heating bill paid back by mining | about 21% |
| Mining revenue over a 180-day heating season | about $589 |
Figures use the Bitcoin hashprice of $40.93 per PH/s per day on 21 September 2026 (Hashrate Index) and move with the Bitcoin price and network difficulty. 21energy quotes a higher seasonal "cashback" (€881) because it assumes the four-year average Bitcoin price rather than today's hashprice. Mining revenue per terahash is expected to roughly halve at the next halving, around April 2028.
Honest comparison: the Ofen 3 competes with direct electric heaters, oil-filled radiators and infrared panels, where the same electricity would produce the same heat and earn nothing. If your home already runs on a heat pump, a heat pump delivers roughly three times more heat per kWh, and a Bitcoin heater will cost more to run than that heat pump. Our 21energy heater guide works through both cases.
What’s in the Box
- 21energy Ofen 3 Base XL heater
- Power cable
- User manual (setup video available from 21energy)
Why Buy from BullMiners?
- Genuine, new hardware: sourced through authorised channels, never refurbished units sold as new
- EU support: help with setup, pool configuration and warranty claims in your time zone
- Keep 100% of what you mine: it mines to your own pool account and wallet – we never touch your coins
- Crypto checkout: pay in Bitcoin, USDT/USDC on your preferred network, or 25+ other coins
- Honest numbers: every figure on this page is dated and sourced, so you know exactly what you are buying