21energy Ofen 3 Base

• Heat output: 1.0 kW
• Suitable for rooms up to: 50 m²
• Hashrate: 40 TH/s
• Efficiency: 20 J/TH
• Noise level: about 35 dB
• Dimensions (w × h × d): 90 × 32 × 14 cm
• Weight: about 17 kg
• Power connection: regular wall outlet, 230 V
• Network: Wi-Fi
• Controls: 21energy app (iOS, Android), Home Assistant, open API
• Thermostat: yes, via the included RuuviTag
• Colors: white, black
• Warranty: 12-month manufacturer's warranty plus statutory rights
• Delivery time: 3 to 5 business days
• Made in: Austria

Buy the 21energy Ofen 3 Base: heat your room and mine bitcoin at the same time

The 21energy Ofen 3 Base is a 1 kW wall heater with a bitcoin miner inside. The heat is exactly the same as from any other 1 kW electric heater; the difference is that the chips producing the heat work on the Bitcoin network in the meantime, at 40 TH/s, and you get sats back for it. It's the entry model of the series and, at 14 centimeters deep, the slimmest of the four. At 35 dB it's quieter than a fridge, so it can go in a living room, bedroom or home office. This is the Ofen to start with if you've never had a miner in your home.

How the Ofen 3 works

A bitcoin miner turns almost all the electricity it uses into heat; that's physics, not a side effect. 21energy builds a heater around it: chips in a closed housing with a quiet fan, warm air out the top, and in the meantime the miner works on the Bitcoin network. You set it up in three minutes with the 21energy app: connect to Wi-Fi, enter your pool details, done. Schedules, a thermostat via the included RuuviTag, Home Assistant and an open API are all built in. The mined bitcoin arrives in your pool account and you send it on to your own wallet.

Honest about the costs

At the average Dutch electricity rate, electric heating costs more than gas or a heat pump, even with a miner inside. The Ofen 3 is, however, the cheapest way to heat electrically, because every other electric heater gives nothing back. It fits three situations: solar panels with a dynamic contract, a room without central heating (garage, workshop, studio, tiny house), or you're a bitcoiner and you simply want one. Heating a regular home with gas and mainly looking to save money? Then this isn't your product, and we'd rather tell you now than after delivery.

Reference date late August 2026: electricity €0.30 per kWh, hashprice 38 USD per PH/s per day, 1 USD = 0.90 EUR, gas €0.15 per kWh of heat. The hashprice moves daily with the price and the network, so what you mine is never a fixed amount. What is certain: the Ofen uses exactly as much as a regular heater of the same power, and everything the miner earns comes off that. The full calculation is on the category page bitcoin heating.

Base or Pro?

The Base and the Ofen 3 Pro share the same housing, give the same heat and make the same noise. The only difference is the miner inside: 40 TH/s at 20 J/TH in the Base, 60 TH/s at 17.5 J/TH in the Pro. The Pro gets about a third more hashrate per kilowatt-hour from the same electricity and costs about 800 euros more. If you heat a few hours a day in winter, the Base is the logical choice. If the heater runs for hours every day for half the year, look at the Pro.

All four models side by side

What's in the box

• The Ofen 3 itself, in white or black
• Basic stand to set it up freestanding
• RuuviTag temperature sensor for the thermostat function
• Power cable for a regular wall outlet
• Quick start guide

A wall mount or the premium stand is sold separately.