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For a directly documented, air-cooled machine, the Antminer S21 XP is the efficiency leader in this comparison: 270 TH/s, 3,645 W at the wall, and 13.5 J/TH at a 25 °C inlet temperature. A lower J/TH means less electricity for each unit of SHA-256 hashing, but the best purchase depends on delivered wall power, cooling overhead, electricity tariff, uptime, and installation cost—not the nameplate number alone.
The short answer
Bitmain’s Antminer S21 XP is the strongest air-cooled reference point in the available specifications. Its published 13.5 J/TH is substantially below the documented figures for MicroBT’s air-cooled WhatsMiner M60S (18.5 J/T) and M60S+ (17 J/T). Bitmain rates the S21 XP at 270 TH/s and 3,645 W, while the M60S family covers lower hashrate and power ranges.
Hydro-cooled hardware can advertise an even lower nominal figure. One current comparison lists the Antminer S21 XP Hydro at about 12 J/TH. That is a different cooling configuration, however. Coolant pumps, heat exchangers, plumbing, controls, facility power and hosting charges must be included before comparing its total electricity use with an air-cooled unit.
The practical decision rule is simple: use J/TH to narrow the list, then compare the complete installed system at your site’s temperature, voltage, tariff and uptime.
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What J/TH means for Bitcoin mining
Joules per terahash
J/TH (also written J/T) is energy consumed at the wall for one terahash of SHA-256 work. Lower is better. It is the most useful first-pass metric when the goal is maximizing Bitcoin production per kilowatt-hour because it normalizes machines with different hashrates.
The basic calculation is:
J/TH = wall watts ÷ hashrate in TH/s
For the S21 XP, 3,645 W divided by 270 TH/s equals 13.5 J/TH. A machine with more TH/s can still be worse for an electricity-constrained operation if it consumes proportionally more watts.
What the number does not include
Manufacturer efficiency is normally a machine-level, wall-power figure. It does not automatically include room ventilation, air-conditioning, pumps, heat rejection, power-distribution losses, networking equipment, hosting charges or downtime. Those items determine the efficiency of the mining installation rather than the ASIC alone.
Published specifications compared
| Model | Cooling | Published hashrate | Wall power | Published efficiency | Specification conditions |
|---|---|---|---|---|---|
| Antminer S21 XP | Air | 270 TH/s | 3,645 W | 13.5 J/TH | Typical values at 25 °C; hashrate can vary about ±3%, wall power and efficiency about ±5% (Bitmain, 2024) |
| WhatsMiner M60S | Air | 170–186 TH/s | 3,145–3,441 W | 18.5 J/T ±5% | At 25 °C (MicroBT, 2024) |
| WhatsMiner M60S+ | Air | 190–210 TH/s | 3,230–3,570 W | 17 J/T ±5% | At 25 °C (MicroBT, 2024) |
| Antminer S21 XP Hydro | Hydro | Not stated in the comparison | Not stated in the comparison | About 12 J/TH | Different cooling system; figure is not directly comparable to an air-cooled wall figure without facility overhead |
The S21 XP’s 13.5 J/TH is about 27% lower than the M60S’s 18.5 J/T and about 21% lower than the M60S+’s 17 J/T when comparing the published nominal values. These are nameplate comparisons, not a guarantee of equal delivered performance in every installation.
Antminer S21 XP: the air-cooled efficiency benchmark
What you get
- 270 TH/s rated hashrate.
- 3,645 W typical wall power.
- 13.5 J/TH typical wall efficiency at 25 °C.
- SHA-256 support for BTC, BCH and BSV.
- 220–277 V AC input and a 20 A single-phase requirement.
Bitmain describes the quoted values as typical rather than fixed. Its specification wording says actual hashrate fluctuates by approximately ±3%, while actual wall power and wall efficiency fluctuate by approximately ±5%. Treat 13.5 J/TH as a design point and verify the delivered unit with a suitable meter.
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Energy use from the nameplate
At continuous 3,645 W operation, the arithmetic is 3.645 kW × 24 hours = 87.48 kWh per day. A 30-day month is approximately 2,624.4 kWh, and a 365-day year is approximately 31,930 kWh. These figures describe the miner only and assume uninterrupted operation at the published power; they exclude cooling, distribution losses and downtime.
Temperature matters
Bitmain’s manual shows efficiency worsening as ambient temperature rises. The 25 °C figure therefore should not be treated as a universal result for a hot room, a restricted intake or a recirculating exhaust stream. Keep the inlet environment within the manufacturer’s limits, measure temperature at the miner intake, and account for seasonal derating when forecasting production.
WhatsMiner M60S and M60S+: documented alternatives
WhatsMiner M60S
The M60S is specified at 170–186 TH/s and 3,145–3,441 W, with 18.5 J/T ±5% at 25 °C. The range reflects configurations rather than a single guaranteed operating point. At the low and high power figures, continuous energy use is approximately 75.48–82.58 kWh per day before facility overhead.
WhatsMiner M60S+
The M60S+ is rated at 190–210 TH/s and 3,230–3,570 W, with 17 J/T ±5% at 25 °C. Its continuous miner-only energy arithmetic is approximately 77.52–85.68 kWh per day. It offers more hashrate than the M60S while retaining a higher published J/T than the S21 XP.
Shared deployment requirements
MicroBT specifies 220–240 V AC, Ethernet connectivity, substantial airflow and an IEC C19 high-current cable for both models. Confirm the exact inlet connector, cable rating and protection device for the batch you are buying; a household extension lead is not an adequate substitute for correctly rated distribution equipment.
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Air cooling versus hydro cooling
Air-cooled systems
Air cooling is simpler to deploy: connect the miner to correctly rated power and Ethernet, provide a controlled intake and exhaust path, and maintain filters and fans. The trade-offs are high heat output, high noise and sensitivity to room temperature and airflow restrictions. Every watt consumed becomes approximately one watt of heat that the room must remove.
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Hydro cooling can produce a lower ASIC-level J/TH, with the S21 XP Hydro listed at about 12 J/TH in one comparison. It also adds a thermal loop. Pumps, coolant, heat exchangers, manifolds, leak management, controls and a way to reject heat all consume money and, in some designs, additional electricity. A hydro unit may be superior at a facility designed for liquid cooling, but the nominal 12 J/TH cannot be used as a stand-alone site-efficiency result.
How to make a fair comparison
- Record the ASIC’s actual wall watts and hashrate.
- Add power for pumps, fans, controls, heat exchangers and other cooling equipment.
- Include power-distribution losses and networking loads.
- Divide total facility watts by delivered hashrate to obtain an installed J/TH.
- Compare uptime and maintenance requirements over the same period.
Electrical service and cabling
S21 XP electrical planning
The S21 XP calls for 220–277 V AC and 20 A single-phase input. Have an electrician verify that the service, breaker, receptacle or power distribution unit and continuous-load calculations comply with local electrical rules. The miner’s 3,645 W nameplate is close to the practical limit of a 20 A circuit once continuous-load derating and other connected equipment are considered.
M60S-series planning
The M60S and M60S+ specify 220–240 V AC and an IEC C19 high-current cable. Match the cable, connector, PDU and breaker to the actual voltage and current. Ethernet is required for management and pool connectivity, so plan a reliable wired network rather than relying on marginal wireless coverage.
Commissioning checks
- Measure voltage under load at the miner’s input.
- Use a meter or monitored PDU that can report real wall power.
- Inspect plugs and connectors for heat discoloration after the first hours of operation.
- Keep intake and exhaust paths physically separated to prevent hot-air recirculation.
- Label each circuit so a fault can be isolated without shutting down unrelated equipment.
Electricity cost and the halving effect
Electricity is usually the dominant operating expense in a mining operation. An AlixPartners/AMINA analysis of weighted public-miner data reported electricity at about 68% of cash costs before the halving and 71% after the halving in its 2025 analysis. The exact share varies by operator, tariff, hardware age and hosting arrangement, but the direction is clear: a small J/TH advantage can matter more than a modest difference in purchase price.
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Calculate your miner-only energy bill
Use:
daily kWh = wall watts ÷ 1,000 × 24
daily electricity cost = daily kWh × your all-in tariff
For the S21 XP’s 87.48 kWh per day, an illustrative tariff of $0.05/kWh produces $4.37 per day, while $0.10/kWh produces $8.75 per day. Over 30 days those arithmetic results are approximately $131 and $262, respectively. These examples are not forecasts: replace the tariff with your energy charge, demand charge, taxes and hosting rate, then add cooling and distribution overhead.
Include demand and facility charges
A tariff can contain energy, demand, network, taxes and fixed charges. A 3.6 kW miner that runs continuously may create a different demand profile from a briefly operated appliance. If you use colocation, ask whether the quoted rate includes cooling, power conversion, internet access, repairs, curtailment and restart fees. Compare the complete monthly invoice rather than the energy line alone.
Hashrate, uptime and pool results
J/TH is necessary but not sufficient. Bitcoin output also depends on uptime, pool fees, firmware stability, rejected shares, thermal throttling and maintenance intervals. A less efficient machine that runs reliably can outperform a more efficient one that is frequently offline or derated.
Measure delivered performance
- Log wall watts, inlet temperature and reported hashrate after the miner reaches steady state.
- Record pool-side accepted hashrate over several days, not only the local dashboard figure.
- Track restarts, rejected shares, thermal alarms and fan faults.
- Calculate observed J/TH from measured wall watts divided by accepted or averaged hashrate.
- Recheck after ambient temperature changes or firmware updates.
Use the manufacturer tolerance when setting expectations. For the S21 XP, a ±5% power variation means a measured result around the nominal value is not automatically a defect; investigate sustained deviations, unstable temperatures and repeated alarms.
Best Value
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Choosing by operating environment
Choose the S21 XP when
- You need the lowest documented air-cooled J/TH in this comparison.
- Your site can supply 220–277 V AC on a properly designed 20 A single-phase circuit.
- You can remove approximately 3.6 kW of continuous heat per unit and tolerate industrial fan noise.
- Your tariff makes every percentage of energy efficiency valuable.
Choose an M60S when
- Your available budget or supply chain favors the documented 170–186 TH/s configuration.
- The 220–240 V AC service and IEC C19 distribution are already available.
- You can accept the higher 18.5 J/T nominal efficiency in exchange for the specific unit’s price or availability.
Choose an M60S+ when
- You want 190–210 TH/s in the M60S family.
- Your facility can support up to 3,570 W per unit and the associated airflow.
- The purchase and hosting terms compensate for its 17 J/T nominal efficiency relative to the S21 XP.
Consider hydro cooling when
- You already operate a liquid-cooling loop or a host provides one as part of the contract.
- Air temperature, noise or heat rejection is the limiting constraint.
- You have a documented total-system power figure, not only the ASIC’s nominal J/TH.
Installation checklist
- Confirm the electrical design. Verify voltage, phase, breaker capacity, continuous-load calculations, receptacles, PDU ratings and cable type.
- Plan heat removal. Size intake and exhaust paths for continuous operation; do not assume a domestic room can dissipate several kilowatts indefinitely.
- Provide network access. Use wired Ethernet, reserve an address or documented discovery method, and restrict management access from the public internet.
- Install monitoring. Capture wall watts, temperature, fan status, hashrate and pool-side accepted work.
- Commission gradually. Start one unit, inspect voltage and connector temperature, then add machines while checking the facility’s total load.
- Document maintenance. Keep records of dust cleaning, fan replacement, firmware changes, thermal events and downtime.
Common mistakes and how to avoid them
Comparing only TH/s
TH/s measures throughput, not energy efficiency. Divide wall watts by hashrate and compare J/TH at the same inlet temperature.
Treating a hydro figure as an air figure
A hydro-cooled 12 J/TH listing does not prove a 12 J/TH installed facility. Add the liquid loop and heat-rejection loads before making a purchase decision.
Using room temperature instead of inlet temperature
The air entering the miner may be hotter than the thermostat reading because of recirculation or poor ducting. Measure at the intake and account for the manufacturer’s temperature dependence.
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Typical values are not guarantees. The S21 XP’s stated tolerances are approximately ±3% for hashrate and ±5% for wall power and efficiency; the M60S specifications include ±5% efficiency tolerance.
Under-sizing infrastructure
Power, Ethernet and cooling must be designed for continuous load. A cable or breaker that is acceptable for a brief appliance load may be unsuitable for an always-on ASIC.
Decision framework
| Priority | What to compare | Why it matters |
|---|---|---|
| Energy efficiency | Measured wall J/TH at your inlet temperature | Determines electricity required for a given amount of hashing |
| Capacity | TH/s and number of units your service can support | Sets total output and electrical load |
| Thermal design | Airflow or complete liquid-loop power and heat rejection | Prevents derating and captures facility overhead |
| Reliability | Uptime, accepted pool hashrate, faults and maintenance | Turns theoretical output into realized output |
| Economics | Energy, demand, hosting, cooling, capital and resale assumptions | Determines whether efficiency translates into acceptable operating cost |
On the published numbers alone, the S21 XP is the first air-cooled model to evaluate. The M60S and M60S+ remain credible alternatives when their acquisition, hosting or electrical circumstances are better. Hydro equipment deserves a separate installed-system calculation rather than a direct ASIC-only ranking.
Quick Recap
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