Pencil drawing of the 21energy Ofen 3 Base

Space heater Floor standing In production

21energy Ofen 3 Base

The entry model of 21energy's Ofen 3 range: a slim 1 kW heater whose warmth comes from mining chips (up to 40 TH/s). Five heat levels, a thermostat mode, app and Home Assistant control. Made in Austria, shipping since October 2026; the shop quotes about one to two weeks for delivery.

Best price $1,845

$46.13 per TH · New · In stock at 21energy · excl. tax

delivery window shown Nov 11-18 (white or black, same price)

Reviews from Nostr ↓

Hashrate40 TH/s worst 250 GH/sbest 1.16 PH/s 136th best of 197 (the bar uses a log scale)
Power (stock)1,000 W lowest 11 Whighest 22 kW 148th highest of 199 (the bar uses a log scale)
Efficiency25 J/TH worst 100 J/THbest 8.9 J/TH 148th best of 195
Earns per kWh$0.061 worst $0.010best $0.171 148th best of 195
Heat output3,412 BTU/h worst 38 BTU/hbest 75,067 BTU/h 148th best of 199 (the bar uses a log scale)
Noise35–45 dB worst 76 dBbest 25 dB 30th best of 68
Price per TH$46.13 worst $539.96best $1.82 124th best of 156 (the bar uses a log scale)

Where to buy

Store Trustpilot Condition Availability Listed price In your currency Per TH Checked Link
21energy Ships from Austria · Maker's own shop delivery window shown Nov 11-18 (white or black, same price) TrustScore 4.8 out of 5, 1,194 reviews New In stock €1,658 excl. tax $1,845 $46.13 4 Nov 2026 Visit

Prices as listed on each store's page on the date shown, without shipping. Prices marked excl. tax leave out VAT or sales tax, and others may too. Per TH uses the hashrate of the unit each store sells. Converted at ECB rates of 11 Nov 2026. Trustpilot scores are for the store, not the device. Each store's name opens its page, with everything it sells and its reviews.

Heat, running cost and sats

Heat per day
—
Electricity per day
—
Mining earns per day*
—
Net cost per day
—
Net cost per kWh of heat
—
Solo: chance of a block per year
—
Earns per kWh, on 3-month averages
—
Payback
—

*What a pool would pay on average at today's difficulty, block reward and bitcoin price, before pool fees. Solo miners usually earn nothing, and very rarely a whole block. A plain electric heater turns the same electricity into the same heat, so the mining income is what makes the difference.

Payback is how long the bitcoin a device earns takes to add up to its price. It leaves out electricity, which buys the heat: compare earnings per kWh with your electricity price to see whether mining alone covers it. It uses the average of the last 3 months, to 12 Nov 2026: bitcoin at $79,558, 969 EH/s on the network and 3.15 BTC a block, less a 2% pool fee, for the hours you set. It cuts the block subsidy in half at each halving, the next around Apr 2028, and otherwise assumes those carry on unchanged, which they won't. Income at today's difficulty and price is about 17% below that average. Hashrate usually rises, though miners that stop paying after a halving may switch off, which leaves more for the rest. How we work it out.

Specifications

Brand21energy
ModelOfen 3 Base
SKUH-21-OF3-XXXXW40-N-X (white) / H-21-OF3-XXXXB40-N-X (black)
TypeSpace heater · Home
Form factorFloor standing
CoolingAir
Production statusIn production
Launch dateOct 2026 *
Hashrate40 TH/s
Power consumption (stock)1,000 W
Mining efficiency25 J/TH *
ASIC chipNot known yet
Heat output3,412 BTU/h
Input voltage230 V AC
Frequency50 Hz
Net dimensions (W × D × H)900 × 140 × 320 mm (35.4 × 5.5 × 12.6 in) *
Net weight17 kg (37.5 lb)
Noise35–45 dB *
Operating temperature10–35 °C (50–95 °F)
Area heated50 m² (maker's claim)
ColoursWhite, Black
Company based inAustria
Made inAustria

* Not confirmed by the maker's own documents yet.

Heat modes

ModeHashratePowerHeat
Level 112 TH/s300 W1,024 BTU/h
Level 218 TH/s450 W1,535 BTU/h
Level 328 TH/s650 W2,218 BTU/h
Level 432 TH/s825 W2,815 BTU/h
Level 540 TH/s1,000 W3,412 BTU/h

Features

  • Five heat levels plus thermostat mode
  • 21energy app over Wi-Fi (Bluetooth pairing)
  • Official Home Assistant integration and open local API
  • Schedules and automations
  • Basic stand included; premium stand or wall mount optional
  • CE compliant, tested to EN 60335-2-30 room-heater standard
  • 12-month manufacturer guarantee

Colours

WhiteBlack

Reviews

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Sources and data notes

Not yet confirmed from the maker's own documents: dimensions orientation (published as 90 x 32 x 14 cm); minimum noise (product page says about 35 dB; manual gives max 45 dB at 1 m); launch date (first deliveries announced for Oct 2026; actual first shipment date not confirmed); efficiency (computed from the maker's power and hashrate; 21energy's page states 20 J/TH, which does not match its own 1.0 kW / 40 TH/s and 2.0 kW / 80 TH/s figures).

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