At the hashprice we derived this morning, the 216-terahash Antminer S21+ covers its own electricity at 7.766 pence per kilowatt hour. Octopus published 44 of today's 48 half-hourly Agile rates for Eastern England. The cheapest was 11.02p. Not one reached the line.
The arithmetic comes from live network data, not a calculator site. Difficulty gives a network hashrate of 950.02 exahashes, and the last 144 blocks paid 3.13838253 BTC a block including fees. At £65,303 to the bitcoin, net of a one per cent pool fee, that is £0.030754 per terahash per day. The 216T bin earns £6.64 a day and burns 85.536 kilowatt hours doing it.
Against a real British tariff
The Ofgem cap in force today, covering 1 October to 31 December 2026, is 26.32p per kilowatt hour on direct debit. At that rate the machine loses £15.87 a day; at today's Agile median of 24.49p, £14.30; at the cheapest half-hour, £2.78; at the dearest, 52.50p at teatime, £38.26.
One honest wrinkle. The Agile feed returned identical values in its exclusive and inclusive VAT fields today, which is not usual. Ofgem's own page explains it: there is no VAT on electricity from 1 October 2026 to 31 March 2027. So the cap and the Agile rates compare directly, with no adjustment. Both are specific to Eastern England and to today.
Zero of 44 published half-hours were below break-even. The cheapest was 42 per cent above it.
The one thing it has over the range
Bitmain's product manual specifies single phase, 220 to 277 volts, 20 amps maximum input. Every hydro and immersion variant in the S21 family is 380 to 415 volt three phase and cannot go in a British home at all — and nor, per Bitmain's current manual, can the Antminer T21 we reviewed last week.
The S21+ will run on a UK supply. It will not run on a UK socket. At 230 volts a 13-amp plug tops out at 2,990 watts and this draws 3,564, so it needs a dedicated radial circuit, a 20-amp breaker and an industrial outlet. It throws 3.564 kilowatts of heat continuously and rates 76 dBA. And the detail most reviews skip: Bitmain's own EU declaration of conformity rates it EMC Class A and warns that residential operation “could cause radio interference”.
What you are actually buying
Bitmain no longer sells the air-cooled S21+; its live catalogue returned 37 products this morning without it. The range has moved to the S23 series, whose S23 XP Hyd. is quoted at 8.9 joules per terahash — so at 16.5, the S21+ burns 85 per cent more energy per terahash than the current flagship.
So this is a reseller purchase. The Mining Shop UK listed the 216T bin at £1,700 excluding VAT, in stock — £7.87 per terahash ex-VAT, or £9.44 inclusive.
Warranty is where the secondary market bites. The user guide promises 365 days from shipping. Bitmain's overseas repair guide gives 180 days to “S9 and series launched after S9, except 19 series”, not naming the 21 series at all — and that table decides whether a repair is free. Either way the cover is not yours: Bitmain's terms state the warranty “is non-transferable and is enforceable only by the original purchaser”.
The verdict
The bull case is narrow but real: £7.87 a terahash is cheap, and the machine is single phase at British voltage when most of its family is not. The bear case is that no published British rate today, cap or Agile in this region, comes near 7.766p — so every hour it runs it loses money, while needing an electrician, a 20-amp circuit and a reseller's goodwill instead of a maker's warranty.
| Hashrate, power, efficiency | 216 TH/s, 3,564 W, 16.5 J/TH |
| Network hashrate from difficulty | 950.02 EH/s |
| Block reward, last 144 blocks | 3.13838253 BTC incl. fees |
| Bitcoin price | £65,303 |
| Hashprice, net of 1% pool fee | £0.030754 /TH/day |
| Gross revenue, consumption | £6.64 a day, 85.536 kWh |
| Break-even electricity | 7.766 p/kWh |
| Revenue per megawatt | £1,863.89 a day |
| Ofgem cap, 1 Oct to 31 Dec 2026 | 26.32 p/kWh → −£15.87 a day |
| Agile today: median, cheapest | 24.49p, 11.02p — 0 of 44 below |
| Supply, and reseller price | 1-phase 220–277 V 20 A; £1,700 ex-VAT |
Retrieved and derived 5 October 2026. Difficulty, block reward and fees from mempool.space; bitcoin price in sterling from CoinGecko; half-hourly rates from the Octopus Agile API for Eastern England, product AGILE-24-10-01, of which 44 of 48 were published when we wrote. The 26.32 p/kWh cap is Ofgem's published direct-debit figure for the period in force today; Ofgem also states there is no VAT on electricity from 1 October 2026 to 31 March 2027, which is why the Agile feed returned identical exclusive and inclusive VAT values and why no VAT adjustment is applied. Specifications, electrical requirements, noise, the declaration of conformity and warranty terms are from Bitmain's own S21+ product manual 1.1.3, user guide 1.2.0, terms and overseas repair guide, re-read from Bitmain's asset host while checking this piece; catalogue absence from Bitmain's product API; reseller price from The Mining Shop UK. Contested: the manual gives the middle bin as 226 TH/s and the user guide 225; warranty is 365 days in the user guide against 180 in the repair guide table, which does not name the 21 series. Profitability is derived from live network data, not a calculator, and every rate is specific to Eastern England and to today. Not a recommendation to buy, sell or hold anything, or to mine.