21energy is at the forefront of a transformative sustainable heating solution — turning heat from Bitcoin mining into warmth for homes. The Austrian company’s approach puts the heat generated by computing to practical use, with the environmental benefit depending on the electricity source and the heating it replaces. Bringing the idea into everyday living spaces has meant making the hardware quieter, simplifying setup and giving customers an easy way to control room temperature.
RuuviTag has become an integral part of 21energy’s product development journey, providing room-temperature measurements across successive generations of its Bitcoin heaters.
We spoke with Benjamin Kehrer, Chief Marketing Officer at 21energy, about the company’s journey, why it chose Ruuvi and what customers experience when the two products work together.
From a home experiment to a heating business
The story began in 2021, when 21energy’s founder experimented with using mining equipment to heat his own home.
“He built himself a prototype for the upcoming winter,” Benjamin recalls.
After using it through the heating season, the founder saw an opportunity to make the idea available to a wider audience. Heat that would otherwise need to be removed from the equipment could instead serve a household need.
“Normally the heat is a burden. Why not turn that burden into a usable product?”
The experiment led to the company’s founding in 2022. Based in Innsbruck, Austria, the team set out to turn the concept into a product that people could install and use without becoming mining specialists.
Its earliest customers were already interested in Bitcoin and understood the idea quickly. Over time, interest expanded to people with rooftop solar panels and smart home systems. These customers were exploring ways to use their own electricity and connect heating to the rest of their home.
“Our next step is the general public.”
Reaching that audience meant making the technology fit naturally into people’s homes.
Making a heater people can live with
Making that transition meant addressing noise, ease of use and design.
Conventional mining hardware can be too loud for a living space. As Benjamin puts it:
“It’s like a starting jet plane right next to you in the living room, and you don’t want to have a jet plane in your living room.”
Reducing that noise was essential. The team also developed its own app so customers could connect the heater to Wi-Fi and manage it from a smartphone, without having to learn how to operate the underlying mining equipment.
Appearance mattered too. The earliest devices looked like small black tables. Later designs made their purpose as heaters more recognisable, while the team continued working on how they would fit into people’s homes.
The Ofen range has since progressed through several generations, with RuuviTag included in both Ofen 2 variants and all four Ofen 3 models: Base, Base XL, Pro and Pro XL.
Across that development, the everyday requirement stayed familiar: customers wanted to choose a comfortable temperature and let the system manage the heating.
Why 21energy chose RuuviTag
When selecting a sensor, 21energy evaluated several alternatives. Its first consideration was how easily the measurements could be integrated into its own system.
“We tried a couple of competitors as well, and Ruuvi was the easiest solution to go with,” Benjamin says. “We could easily get the data.”
Ruuvi’s documentation and open-source approach also helped with the integration:
“That made it really smooth to incorporate into our system, and I think that’s a win for you guys.”
The physical design supported the decision. A room sensor becomes part of someone’s home, so its appearance and placement matter alongside its technical capabilities. The team valued RuuviTag’s understated design, low weight and flexibility in where it could be placed.
Using an existing sensor also helped 21energy concentrate its development efforts. The team was still making substantial improvements to its heaters, with a central heating system also on the roadmap.
“Our roadmap is still quite long, with many tasks, and developing our own sensor is not on it right now.”
For 21energy, RuuviTag provided an established component around which the team could build its own heating experience.
From a temperature measurement to a comfortable room
Setup begins with customers unpacking their heater, plugging it in and using the 21energy app to connect it to their home Wi-Fi. Connecting the RuuviTag is also part of the initial setup.
Once configured, customers can choose heating levels manually or set a target room temperature. RuuviTag supplies the temperature measurement, while 21energy’s system provides the thermostat logic and controls the heater.
The distinction matters: the sensor measures conditions in the room, and the heating system uses that information to act on the customer’s chosen temperature.
“RuuviTag is essential for this feature, and it will be essential in the future as well because we’re not developing our own sensors.”
Customers can also see the temperature in the 21energy app. With the heater connected to the internet, the app allows them to manage it remotely.
The result is a familiar interaction with an unusual heating technology: choose the temperature you want, check the room’s conditions and adjust the heating through the app.
What customers ask about Ruuvi
For customers, the sensor’s role becomes practical as soon as they set up their heater. At 21energy, the most common customer questions about RuuviTag concern placement:
“What is the perfect height in the room? Where should I place it? Should I place it in the corner or somewhere else?”
People want to know how to position the sensor so that the system receives a useful picture of room temperature. Clear setup guidance helps them get started with the thermostat feature and use it confidently in their own homes.
The next step: central heating and hot water
21energy’s upcoming central heating solution will extend Bitcoin heating beyond individual rooms, connecting a water-cooled miner to a storage tank to supply radiators, underfloor heating and domestic hot water. The system is planned for launch in Q4 2026, with a waiting list already open for interested customers.
For 21energy, hot water is an important part of that development. Households need it throughout the year, extending the opportunity beyond the usual room-heating season.
“Whether you need warm air or warm water, both are based on Bitcoin.”
The new system would extend 21energy’s concept to that continuing demand.
The principle remains the same: use the heat produced by mining for a household need. Any financial benefit depends on factors including electricity costs, operating conditions and mining returns.
A shared focus on everyday usability
21energy’s journey shows how much work sits between a technical idea and a product people can use comfortably at home. Quieter hardware, approachable controls and a suitable design all play a part.
RuuviTag contributes the room-temperature measurement that makes a key feature possible. For 21energy, choosing an existing sensor helped keep development focused on the heating products. For its customers, it means being able to set a target temperature and see how warm the room is through the same app they use to manage their heater.
As 21energy develops its next generation of heating solutions, that focus on everyday usability continues to shape its direction.
Put RuuviTag to work in your own setup
Reliable wireless monitoring for temperature, humidity, air pressure and motion.
39,90€
Ruuvi is based in Finland. If you’re an EU consumer, VAT is included. If you’re a non-EU customer, you don't pay VAT. If you're an EU business, insert your VAT ID at checkout.
RuuviTag Sensor (4in1)
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RuuviTag Sensor (4in1)
| Quantity | Unit Price(€) |
|---|---|
| 1 | 39,90 |
| 2 | 37,40 |
| 3-5 | 36,90 |
| 6-8 | 35,90 |
| 9-12 | 34,90 |
| 13-25 | 33,90 |
| 26-99 | 32,90 |
Are you looking for bigger quantities? Contact us for pricing.
Made in Europe, Finland. Worldwide free shipping on orders over 120€.
RuuviTag is a Bluetooth sensor that monitors environmental conditions and sends the data directly to your mobile device. The Ruuvi Station mobile app allows you to view real-time accurate measurements and historical graphs. The app also provides customisable alerts to notify you of critical conditions, such as a melting freezer, excessively high bedroom temperatures that could disrupt sleep, or elevated humidity levels in your basement.
Onboard Sensors (4-in-1)
Temperature: °C, °F, K; typical accuracy ±0,2 °C @ 5-60 °C (±0.36 °F @ 41-140 °F).
Air humidity: RH-%, g/m3, dew point; typical accuracy ±3 RH-% @ 20…80 %. Range: 0-95 %.
Air pressure: Pa, hPa, mmHg, inHg; typical accuracy ±1 hPa. Range: 500-1155 hPa.
Motion: Movement counter. Counter is incremented when acceleration exceeds the threshold on any axis.
Operational Conditions
Operating temperature (with stock battery): -20 °C to +70 °C (-4 °F to 158 °F).
Absolute maximum operating temperature: -40 °C to +85 °C (-40 °F to +185 °F).
Housing: IP67, splash-proof, non-condensing location.
Battery: User-replaceable CR2477 (included). Supports extended operating temperature range battery CR2477T.
Battery lifespan: Estimated 12 to 24 months.
Certifications: CE, FCC, ISED, TELEC, IFETEL, NOM, RTCA DO-160 category H, RoHS, IC, HVIN, IMDA, OFCA, ICASA, POTRAZ.
Bluetooth range: 5-20 meters (indoor), 20-100 meters (outdoor). The sensitivity of the receiving mobile device’s antenna, obstacles and wall materials affect the range. For increased range, use the Ruuvi Gateway router as a receiver.
App Features
Free and easy: User-friendly free app, signing in is optional.
Platforms: Android and iOS.
Alerts: Configurable Bluetooth push alerts with customisable messages.
Real-time measurements: Track data in real time.
Historical data: Detailed historical graphs available for up to 10 days (offline).
History export: 10-day history export.
Dashboard: See all your sensors at a glance.
Personalise sensors: Use custom backgrounds and names.
Multilingual: Available in English, Finnish, Swedish, French, and German.
Compatibility
Integrations: Victron Energy, Home Assistant, Homey, and more.
Remote monitoring: When not within Bluetooth range, online remote monitoring is available with the Ruuvi Gateway and Ruuvi Cloud, both sold separately.
Technical Specifications
Data sheet: Download (pdf)
Read more info below:
Excellent. Super technology that seamless integrated to my Victron CerboGX/VRM. I highly recommend!
⭐⭐⭐⭐⭐ Excellent sensors for RV monitoring and Victron VRM integration
I am extremely satisfied with my Ruuvi sensors.
I use several of them in different locations inside my motorhome: in the refrigerator, battery compartment, living area, kitchen area and other positions. Installation was very simple and the sensors have been working flawlessly from day one.
What impressed me most is the excellent integration with the Victron ecosystem. Through Victron VRM I can monitor all sensor data remotely 24/7, which is incredibly useful when living and travelling off-grid.
The accuracy is outstanding. The pressure readings of different sensors are almost identical, showing only minimal differences, which gives me great confidence in the quality of the measurements. Temperature and humidity readings have also proven to be very reliable.
I have even used the sensors to evaluate the performance of a portable compressor cooler. Thanks to the precise temperature logging, I was able to see that the cooler dropped from 20°C to 0°C in about 30 minutes and reached -20°C in less than an hour. Without Ruuvi sensors, such testing would have been much more difficult.
Battery life has been excellent, setup is easy, and the overall user experience is outstanding.
For anyone using Victron equipment, RVs, boats, off-grid systems, refrigerators, freezers or environmental monitoring, I can highly recommend Ruuvi sensors.
Hard to say anything bad. It does exactly what it promises.
Excellent!
After integrating four RuuviTags into my Victron Cerbo GX / VRM system in our Rapido motorhome, I can honestly say they have transformed the way I monitor the vehicle.
The setup now provides live temperature, humidity and pressure monitoring directly inside the VRM portal, allowing me to monitor critical areas including:
Battery Box
Orion DC-DC Charger Compartment
Engel Fridge
Main Rapido Fridge Area
What impressed me most was how seamlessly the RuuviTags integrated with the Cerbo GX via Bluetooth. Once connected, the data appears natively inside VRM and can be used for real alarms and automation.
I have now configured:
High temperature alarms
Low temperature alarms
VRM email notifications
Relay-triggered audible siren alarms
The system is now capable of warning me immediately if:
the lithium battery compartment gets dangerously cold
the battery box overheats
the Orion compartment becomes too hot
ventilation or airflow problems occur
The accuracy and stability of the readings have been excellent. The tags update reliably and provide a very clear picture of what is happening inside the motorhome.
One of the major advantages is that the system no longer relies on older digital-input alarm methods or complex workarounds. The RuuviTag + Cerbo GX combination feels like a modern, professional-grade monitoring solution.
The compact size, long battery life and wireless operation make installation extremely easy. No extra wiring was required for the sensors themselves.
For anyone building a Victron-based off-grid system, especially in a motorhome, caravan, marine or lithium battery installation, I would highly recommend RuuviTags.
They add a level of visibility and protection that is difficult to achieve any other way at this price point.
Works well and bluetooth connection works from quite far away even with a few walls in between.