Short answer: lower J/TH usually lowers the energy needed for a unit of hash output, but it is only one purchase input. Before choosing a miner, compare the exact SKU’s stated test condition with measured wall power, pool-side accepted hashrate, your complete tariff, electrical capacity, cooling path, and any heat you can actually use.
J/TH: The Efficiency Number, Defined
J/TH = watts ÷ terahashes per second. One watt divided by one TH/s equals one J/TH. Lower is better when both numbers use the same boundary and operating condition. J/TH is an energy-intensity metric, not a profitability guarantee.
Nameplate, Measured Wall Power, and Accepted Hashrate
| Metric | Definition | Best use |
|---|---|---|
| Nameplate J/TH | Stated wall watts divided by stated TH/s at the manufacturer’s stated test condition. | Initial SKU screening. |
| Measured miner-wall J/TH | Interval-average true AC watts at the miner input, including the onboard PSU and fans, divided by interval-average device hashrate. | Commissioning and troubleshooting. |
| Net productive J/TH | Interval-average miner or facility watts divided by pool-side accepted/effective hashrate over a stated window. | Operating economics. |
Do not mix these measurements. Miner-wall power normally includes the unit’s onboard power-supply losses and fans. Facility power can also include PDU or transformer losses, pumps, dry coolers, ventilation, and controls. Report heat recovery separately rather than subtracting it from J/TH.
Measure Productive Output, Not Just the Dashboard
Device hashrate is the miner’s local report. Pool-side effective or accepted hashrate is inferred from accepted shares, so rejected and stale shares, connection losses, and normal share variance affect it. For an operating decision, record the pool, pool fee, reject rate, outages, firmware/profile, inlet condition, meter boundary, and a 24-hour window; use a longer window for lower-hashrate devices.
Calculate the True Daily Cost
Electricity cost/day = facility kW × 24 × all-in electricity rate
The all-in rate may include energy, delivery, riders, taxes where applicable, demand charges, and time-of-use or tier effects. A full ownership model also includes delivered hardware cost, tax/duty/freight, electrical work, cooling equipment, pool fees, downtime, repair/spares, warranty, and resale assumptions. Recalculate as network conditions and tariffs change.
Heat Recovery Is a Separate, Bounded Credit
Nearly all electricity consumed by a miner ultimately becomes heat. At 3,500 W, that is about 11,943 BTU/h at steady state. Whether it has economic value depends on when and where it is needed.
Net heat credit/day = min(useful recovered heat, heating demand) × avoided heating cost per kWh-thermal − added recovery electricity
The credit cannot exceed the heating expense actually avoided. It may be zero when heat is unwanted, when ventilation discards it, or when the displaced heating system has different fuel or efficiency characteristics. Electricity remains a cost; heat recovery can improve project economics but does not change the miner’s J/TH.
Choose the Exact SKU and Installation, Not a Generation Label
- Enter the complete tariff and any demand-charge exposure.
- Confirm the exact miner’s voltage, phase, plug, current, branch circuit, noise path, and exhaust or heat-recovery plan.
- Compare delivered cost and lifecycle risks, not only purchase price.
- Use the exact SKU’s stated source document and test condition; record the revision and tolerance.
- After commissioning, compare a true-power meter with the pool’s accepted/effective hashrate and investigate material deviations.
Source-Controlled Example Specifications
These are manufacturer nameplate examples, not a current-market ranking or a promise of measured output. The exact revision, inlet condition, tolerance, electrical service, and cooling requirements remain part of the comparison.
| Retained nameplate example | Primary source |
|---|---|
| S21: 200 TH/s, 3,500 W, 17.5 J/TH at 25°C inlet air | Manufacturer specification |
| S21 Pro: 234 TH/s, 3,510 W, 15 J/TH at 25°C inlet air | Manufacturer specification |
| S21 XP: 270 TH/s, 3,645 W, 13.5 J/TH at 25°C inlet air | Manufacturer specification |
| S21 XP Hyd: 473 TH/s, 5,676 W, 12.0 J/TH at 35°C coolant inlet | Manufacturer specification |
| S19j Pro+: 109/113/117/120 TH/s bins, 27.5 J/TH at 25°C inlet air | Manufacturer specification |
The 270 TH/s, 3,645 W, 13.5 J/TH specification belongs to the air-cooled S21 XP, not the S21 XP Hyd. Do not transfer a specification between similar product names or cooling formats.
Commissioning Checklist
- Record the exact model, hashrate bin, model/revision, cooling type, voltage/phase, and source-document version.
- Measure true AC input power at the stated boundary after the machine reaches a stable operating condition.
- Record the device report and pool-side accepted/effective hashrate for the same time window.
- Record inlet temperature or coolant-inlet temperature, firmware/profile, reject rate, outages, and auxiliary loads.
- Keep nameplate, measured, and facility results as separate fields.
Source and Review Standard
Device specifications in this guide are retained only when an exact primary source is linked. A sourced row must state the SKU/bin, revision where available, test condition, tolerance, source date, and editorial verification date. If a manufacturer revises a specification or a newer generation changes the choice set, review the row before presenting it as current.
Related D-Central Resources
Use these related guides, tools, repair references, and product paths after checking the inputs above. A link is not a performance or profitability promise.
- solo mining
- Antminer S9
- Antminer S21
- Antminer S21 Pro
- Antminer S21 XP Hyd
- Mining Profitability Calculator
- Antminer Loki Edition
- Bitcoin Space Heaters
- space heater
- chips
- ASIC repair shop
- Parts
- ASIC Repair
- Antminer S21 Pro
- Antminer S21
- Antminer S21 XP Hyd
- Antminer S19j Pro+
- Bitaxe
- D-Central shop
- Bitaxe Hub
- Bitcoin Space Heaters
- Loki
- ASIC Miner Comparison Tool
- Mining Profitability Calculator
- ASIC Repair
- reach out to our consulting team
- mining training program
- mining hosting in Quebec
Frequently Asked Questions
What does J/TH mean for an ASIC miner?
J/TH means joules per terahash: watts at the measurement boundary divided by terahashes per second. Lower J/TH means less energy per unit of hash output, but comparisons are valid only when the power boundary, operating condition, and hashrate basis are stated.
Is a manufacturer J/TH rating the same as measured performance?
No. A nameplate value is a stated test result for an exact SKU under stated conditions. Measured performance depends on the unit, inlet temperature, firmware profile, meter boundary, and runtime. Record those conditions before comparing the two.
Why can pool-side hashrate differ from the miner display?
The miner display reports local device output. Pool-side effective hashrate is inferred from accepted shares over a time window, so rejected or stale shares, outages, and normal share variance can create a difference. Use a stated 24-hour or longer window for operating decisions.
Does a mining heater make electricity free?
No. Electricity is still purchased. Heat recovery can offset only the avoidable cost of the heating service actually displaced, during periods when that heat is useful, after any added fan, pump, or control energy is counted.
How do I calculate a miner’s daily electricity cost?
Multiply facility kilowatts by 24 and by the all-in electricity rate. Include delivery, riders, taxes where applicable, demand charges, and time-of-use or tier effects. Add cooling and other auxiliary loads when the calculation is for the whole installation.
Can I use a fixed electricity-rate or J/TH profitability threshold?
No fixed threshold guarantees profitability. Use measured power and accepted hashrate with the current network conditions, pool terms, uptime, acquisition cost, repair risk, and several price and difficulty scenarios.
What should be checked before installing a high-power miner at home?
Confirm the exact unit’s input voltage, phase, plug, maximum continuous current, branch-circuit design, airflow path, noise exposure, and heat destination. Use a qualified electrician where required; a family name alone does not establish circuit compatibility.
How should I compare liquid-cooled and air-cooled miners?
Compare the exact SKU and operating boundary. Include the miner wall power, accepted hashrate, inlet condition, electrical service, and the added pumps, heat exchangers, controls, and maintenance required by the cooling system. Do not compare miner-only J/TH with facility-level J/TH.
