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For a buyer focused on Bitcoin mined per kilowatt-hour, the strongest directly documented air-cooled choice in this comparison is Bitmain’s Antminer S21 XP. Its published figures are 270 TH/s, 3,645 watts at the wall and 13.5 J/TH at a 25 °C inlet temperature. Lower joules per terahash means less electricity for the same amount of SHA-256 work.
The S21 XP is not automatically the most profitable machine at every site. Electricity tariffs, demand charges, uptime, pool fees, ambient temperature, ventilation, wiring and the cost of removing heat can outweigh a nominal efficiency advantage. Hydro-cooled miners can publish lower J/TH, but their pumps, heat exchangers, plumbing, controls and hosting requirements must be included in a fair comparison.
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What “Bitcoin per kilowatt-hour” actually measures
Bitcoin ASICs perform SHA-256 calculations. A miner’s hashrate is measured in terahashes per second (TH/s), while its electrical draw is measured in watts. The first-pass efficiency metric is joules per terahash (J/TH, also written J/T): the energy used to perform one terahash of work. Because one watt equals one joule per second, J/TH can be calculated as:
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1Scan for outdated or missing drivers - takes under a minute2Clear out junk files and repair common Windows errors3Fix the driver behind crashes, sound loss and screen glitchesJ/TH = power in watts ÷ hashrate in TH/s.
Lower is better. A 13.5 J/TH machine uses less electricity than an 18.5 J/TH machine when both are delivering their rated hashrate. This metric is a practical proxy for Bitcoin mined per kilowatt-hour because the Bitcoin network rewards valid work, not the number of machines you operate.
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It is not a promise of a fixed number of bitcoins. Your actual coins per kWh also depend on network difficulty, the block subsidy and transaction-fee market, pool payout rules, rejected shares, downtime and firmware behavior. Use J/TH to screen hardware first, then model the whole installation.
Efficiency comparison: the documented miners
| Miner | Cooling | Published hashrate | Published wall power | Published efficiency | Electrical notes |
|---|---|---|---|---|---|
| Bitmain Antminer S21 XP | Air-cooled | 270 TH/s | 3,645 W | 13.5 J/TH at 25 °C | 220–277 V AC; 20 A single-phase input |
| MicroBT WhatsMiner M60S | Air-cooled | 170–186 TH/s | 3,145–3,441 W | 18.5 J/T ±5% at 25 °C | 220–240 V AC; Ethernet; IEC C19 high-current cable |
| MicroBT WhatsMiner M60S+ | Air-cooled | 190–210 TH/s | 3,230–3,570 W | 17 J/T ±5% at 25 °C | 220–240 V AC; Ethernet; IEC C19 high-current cable |
| Bitmain Antminer S21 XP Hydro | Hydro-cooled | Not stated in the cited comparison | Not stated in the cited comparison | Approximately 12 J/TH in a current comparison | Requires a liquid-cooling installation; full auxiliary load not stated |
The S21 XP specification is from Bitmain’s 2024 documentation. Bitmain characterizes the hashrate, wall power and wall efficiency as typical values: actual hashrate can fluctuate by about ±3%, while actual wall power and efficiency can fluctuate by about ±5%. MicroBT gives the M60S and M60S+ figures as ranges with a ±5% efficiency tolerance. The values therefore should be treated as operating specifications, not guaranteed laboratory results for every unit.
Why the Antminer S21 XP leads the air-cooled comparison
At 13.5 J/TH, the S21 XP has the lowest directly documented air-cooled figure in this set. Its 270 TH/s rating also gives it considerably more hashrate per chassis than the M60S family. That combination can reduce the number of machines, network connections and physical spaces needed for a target farm hashrate.
The headline efficiency is measured at a 25 °C inlet temperature. As intake air gets hotter, ASIC chips generally need more electrical power or must reduce frequency to remain within thermal limits. Bitmain’s S21 XP manual shows efficiency worsening as ambient temperature rises, so a room that is comfortable for people but hot at the miner intake can erase part of the paper advantage.
Bitmain identifies the S21 XP as a SHA-256 miner for Bitcoin (BTC), Bitcoin Cash (BCH) and Bitcoin SV (BSV). Mining a different SHA-256 coin does not change the machine’s electrical demand; it changes the market value and payout you receive for the work.
When the M60S or M60S+ makes more sense
WhatsMiner M60S
The M60S is specified at 170–186 TH/s and 3,145–3,441 W, with an efficiency figure of 18.5 J/T ±5% at 25 °C. It is less efficient than the S21 XP on the published numbers, but a lower purchase price, an existing fleet, local service capability or better availability can change the total return on capital.
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WhatsMiner M60S+
The M60S+ raises the documented range to 190–210 TH/s and 3,230–3,570 W, at 17 J/T ±5%. It is the more efficient of the two MicroBT alternatives and sits between the S21 XP and M60S on both hashrate density and power efficiency.
Both models require 220–240 V AC, an Ethernet connection, substantial airflow and an IEC C19 high-current cable. Confirm the exact power-supply unit, connector and breaker arrangement for the seller’s revision; a cable that fits physically is not necessarily rated for the voltage, current or continuous duty of the installation.
Hydro cooling: lower chip efficiency is not the same as lower site energy
A current comparison lists the Antminer S21 XP Hydro at approximately 12 J/TH, below the 13.5 J/TH air-cooled S21 XP figure. That number describes a different cooling configuration. It should not be compared with an air-cooled nameplate unless you add the energy and capital required for pumps, coolant circulation, heat exchangers or dry coolers, controls, filtration, plumbing and the facility that rejects heat.
Hydro cooling can be attractive where rack density, noise or outdoor heat rejection makes fans impractical. It can also introduce leak risk, coolant maintenance, specialized commissioning and a larger minimum project size. Ask the supplier for total system power at the measured inlet temperature, not only the ASIC board figure. If auxiliary consumption is unavailable, mark the hydro option’s site-level J/TH as unknown rather than assuming the nominal 12 J/TH is comparable.
Translate the nameplate into electricity consumption
At continuous operation, the S21 XP’s 3,645 W nameplate equals 3.645 kW. Running for 24 hours uses approximately 87.48 kWh before downtime, pool equipment or cooling overhead; a full year at uninterrupted nameplate power would be about 31,930 kWh. These are arithmetic estimates, not a guarantee that the miner will run at that power every hour.
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| Miner | Approximate daily ASIC energy at published power | Approximate annual ASIC energy at published power |
|---|---|---|
| Antminer S21 XP | 87.48 kWh/day | 31,930 kWh/year |
| WhatsMiner M60S | 75.48–82.58 kWh/day | 27,550–30,140 kWh/year |
| WhatsMiner M60S+ | 77.52–85.68 kWh/day | 28,290–31,280 kWh/year |
For a farm, add the measured consumption of network switches, control systems, ventilation, pumps, lighting and any cooling plant. A facility that draws 10% extra power for cooling and infrastructure has a site efficiency 10% worse than the ASIC-only number, even if the miner itself performs exactly to specification.
Electricity service and cabling requirements
| Requirement | S21 XP | M60S and M60S+ |
|---|---|---|
| Voltage | 220–277 V AC | 220–240 V AC |
| Input arrangement | 20 A single-phase input | High-current single-phase service; verify the exact PSU specification |
| Power connection | Use the manufacturer-specified connector and cable | IEC C19 high-current cable specified |
| Networking | Ethernet control connection | Ethernet control connection |
| Facility needs | Dedicated circuits, airflow and heat removal | Dedicated circuits, airflow and heat removal |
Do not run these machines from ordinary household outlets or extension cords unless an electrician has verified their continuous-current rating, conductor size, connector temperature and protective devices. A 3,645 W load at 220 V is roughly 16.6 A before power-factor and wiring considerations, leaving little margin on a 20 A circuit once continuous-load rules and other equipment are considered.
Have a qualified electrician confirm panel capacity, breaker coordination, grounding, phase balance, disconnects and local electrical code. The miner’s published voltage range does not remove the need to check the actual service voltage under load.
How to compare miners on a real site
1. Start with wall-measured J/TH
Use a calibrated power meter at the miner’s input and record the stable hashrate from the miner dashboard or pool. Divide watts by accepted TH/s. Measure after the machine has reached a steady temperature; startup readings can be misleading.
2. Keep the inlet temperature consistent
Record the air or coolant temperature entering the miner. A 25 °C specification cannot be fairly compared with a test performed at 35 °C. Repeat measurements at the hottest expected operating condition because thermal throttling often appears only during warm periods.
3. Include rejected shares and uptime
Pool-reported hashrate is more useful than a brief dashboard peak. A miner that averages lower uptime or produces more rejected shares can deliver fewer accepted terahashes per kWh than its nameplate suggests. Track accepted, rejected and stale shares over several days.
4. Add every site load
Include fans, air handlers, pumps, heat exchangers, controls, networking, lighting and standby equipment. For hosted mining, ask whether the quoted rate includes cooling, demand charges, repairs and curtailment. If it does not, model those costs separately.
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5. Apply the tariff correctly
Electricity may include an energy charge per kWh, demand charges based on the highest interval load, taxes and time-of-use rates. A miner that runs 24/7 creates a persistent demand peak. Use the utility’s bill structure rather than multiplying a retail headline rate by kWh alone.
Electricity dominates the operating decision
An AlixPartners/AMINA analysis of a weighted public-miner sample found electricity represented about 68% of cash costs before the Bitcoin halving and 71% after the halving. The percentages describe that sample and period, not every home, data center or hosting contract, but they show why a small efficiency difference can matter over thousands of operating hours.
Build a monthly model with these inputs:
- Measured ASIC watts and expected uptime.
- Electricity energy rate, demand charges and taxes.
- Cooling and auxiliary power as a separate load.
- Pool fee and the pool’s payout method.
- Hosting, internet and maintenance charges.
- Purchase price, shipping, installation and expected useful life.
- Bitcoin revenue based on a clearly stated hashrate, network difficulty and BTC price assumption.
A simple electricity-only cost is daily kWh × electricity rate. For the S21 XP, that is 87.48 × your per-kWh rate before cooling and other charges. To compare capital, divide the fully installed cost by expected lifetime accepted TH/s, then add operating costs. Avoid treating a temporary coin price or promotional electricity rate as a permanent return.
Step-by-step deployment checklist
- Confirm the site service. Verify that the panel, breakers, voltage and continuous-load capacity match the miner. Obtain an electrician’s approval before ordering multiple units.
- Choose the cooling layout. For air cooling, design a separated intake and exhaust path so hot exhaust cannot recirculate. For hydro cooling, specify coolant, pumps, heat rejection, leak detection and service access.
- Provide network access. Run Ethernet to each miner or to a managed switch, isolate management interfaces from untrusted networks and document device addresses.
- Install the correct cable. Use the manufacturer-approved connector and a cable rated for the measured voltage, current and continuous operation. Inspect plugs for heat discoloration during the first hours.
- Start one unit first. Record inlet temperature, wall watts, fan or pump behavior, accepted hashrate and rejected shares. Add more units only after the first installation is stable.
- Configure the pool. Enter the pool’s primary and backup stratum addresses, worker name and password. Confirm that the pool sees the expected hashrate and that shares are being accepted.
- Set monitoring and alerts. Alert on loss of hashrate, rising temperature, fan or pump faults, abnormal power draw, high rejected-share percentage and network loss.
- Log a baseline. Save a timestamped record of wall power, hashrate, inlet temperature, firmware version and pool statistics. Use it to detect gradual degradation.
Heat, noise and maintenance constraints
Nearly all electrical power consumed by an ASIC becomes heat. The S21 XP’s 3,645 W load is therefore approximately 3.645 kW of continuous heat at the miner, before room equipment. Exhausting that heat outdoors requires a duct, fan capacity and a weather strategy; recirculating it raises inlet temperature and can trigger throttling.
Air-cooled miners produce substantial fan noise and dust loading. Keep filters and heat sinks clean, but do not restrict airflow with undersized filters or tightly packed racks. Inspect connectors, fans and dust accumulation on a schedule suited to the site. Hydro systems reduce fan dependence but replace some airflow work with coolant quality, pump and heat-exchanger maintenance.
Common mistakes and how to correct them
Comparing J/TH from different cooling systems
Problem: Treating a hydro-cooled 12 J/TH figure as directly equivalent to an air-cooled 13.5 J/TH figure. Correction: calculate total facility watts, including pumps and heat rejection, at the same operating temperature.
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Using a peak hashrate as the economic input
Problem: Forecasting revenue from a short dashboard peak. Correction: use multi-day accepted hashrate and include downtime, stale shares and maintenance windows.
Ignoring temperature derating
Problem: Budgeting from the 25 °C specification in a hotter room. Correction: measure the hottest expected inlet condition and leave airflow capacity for seasonal peaks.
Undersizing circuits or cables
Problem: Plugging a continuous 3-kW-plus load into a general-purpose circuit. Correction: have a qualified electrician design dedicated circuits and verify the IEC C19 or other connector rating.
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Problem: Omitting demand charges, cooling, hosting and capital recovery. Correction: model the complete delivered cost per accepted TH/s.
Which miner fits which priority?
| Priority | Best documented fit | Reason | Qualification |
|---|---|---|---|
| Lowest air-cooled J/TH | Antminer S21 XP | 13.5 J/TH at 25 °C, 270 TH/s | Typical values with stated tolerances; needs 220–277 V AC and 20 A single-phase input |
| Higher efficiency with a MicroBT fleet | WhatsMiner M60S+ | 17 J/T ±5%, 190–210 TH/s | Still requires industrial 220–240 V service and substantial airflow |
| Existing M60S deployment | WhatsMiner M60S | Documented 170–186 TH/s range and 18.5 J/T ±5% | Replacing a working fleet may not recover its capital cost quickly |
| Potentially lower ASIC-only J/TH in a liquid facility | Antminer S21 XP Hydro | Approximately 12 J/TH in a current comparison | Total cooling-system power and infrastructure must be established first |
Due-diligence questions before buying
- Is the quoted hashrate a typical value, a guaranteed minimum or a range?
- At what inlet temperature were power and efficiency measured?
- What tolerance applies to hashrate, wall power and J/TH?
- Does the price include the power supply, approved cables and firmware?
- What warranty covers fans, hash boards, control boards and liquid components?
- Can the seller provide a recent wall-power measurement from the exact revision?
- What are the return, repair and shipping arrangements if a unit arrives defective?
- For hosting, are cooling, demand charges, curtailment and labor included in the quoted rate?
The most defensible starting point is the Antminer S21 XP when the site can supply the required voltage, remove its heat and obtain electricity at a rate that supports continuous operation. The M60S+ and M60S are documented alternatives when fleet compatibility, availability or installed cost matters more than the lowest published J/TH. A hydro-cooled design can win at the facility level, but only after its complete cooling and electrical system is measured.
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