Buy a Bitcoin miner in this order. Confirm you have the electricity, space and noise tolerance for it, choose a machine whose published specifications fit those limits, verify the seller before any money moves, and test the unit as soon as it arrives. Most bad purchases come from skipping the first or the third step, not from picking the wrong model.
Key points
- A full-size air-cooled miner typically draws 3 to 4 kW around the clock. Your electricity price decides whether it can cover its own running cost.
- Read power at the wall, J/TH, input voltage, condition and availability status on a listing, not only hashrate.
- Verify the seller through contact details you found yourself, and treat any change of payment details as fraud until you have confirmed it by phone.
- Know who pays import duty and tax, and what the dead-on-arrival window is, before you pay.
- Film the unboxing and run the machine for at least a full day before the reporting window closes.
Decide four things before you shop
Electricity price
Electricity cost per day = kW × 24 × price per kWh
An illustrative 3.5 kW machine uses 3.5 × 24 = 84 kWh per day. At an illustrative $0.10 per kWh that is $8.40 per day, or $252 over 30 days. Use your all-in tariff including delivery charges and taxes.
Revenue moves with network difficulty and the Bitcoin price, so no article can tell you whether that cost is covered today. Put your tariff and the machine's figures into the calculator. If your tariff is above the break-even electricity price (daily revenue ÷ daily kWh), the machine loses money every day it runs, whatever you paid for it.
Electrical supply
Most full-size miners do not run from a 120 V household socket. Bitmain's published specification for the air-cooled Antminer S21, for example, gives 3,500 W and a single-phase input range of 220 to 277 V. At 240 V and a power factor near 1, that is 3,500 ÷ 240 = 14.6 A, continuously.
That is the typical figure, not the one to size a circuit from. Current rises at lower voltage and at the upper power tolerance (3,675 ÷ 220 = 16.7 A), and Bitmain publishes a maximum input current of 20 A for this model. Under North American practice (NEC), continuous loads are commonly limited to 80% of the breaker rating, so a 20 A breaker carries only 16 A continuously. Other regions follow their own codes. Each machine needs its own dedicated circuit, sized by a qualified electrician from the manufacturer's current rating and local code, not from watts ÷ volts. Do not use adapters or extension leads to work around an unsuitable supply. See 220V Bitcoin Mining.
Heat and noise
Nearly all the power a miner draws becomes heat. 3.5 kW × 3,412 = 11,942 BTU/h, released for as long as the machine runs. It needs a path for cool air in and hot air out. A closed room will overheat.
Bitmain publishes a noise level of 76 dB(A) for the Antminer S21. Machines of this class belong in a garage, outbuilding or hosted facility, not a living space. If noise is your limit, look at home miners, which trade hashrate for low noise.
Cooling type
| Type | What you need besides the miner | Suits a first purchase |
|---|---|---|
| Air | Ventilation, a suitable 200 to 240 V class circuit | Yes |
| Hydro | Coolant loop, pump, heat rejection, usually a three-phase supply | Only with the infrastructure in place |
| Immersion | Tank, dielectric fluid, pump, heat rejection | Only with the infrastructure in place |
Bitmain's published input range for the Antminer S21 XP Hyd. is 380 to 415 V three-phase. A hydro unit is not a plug-in purchase. Air vs Hydro Bitcoin Miners covers the difference.
How to read a listing
| Field | What it tells you | What to check |
|---|---|---|
| Hashrate (TH/s) | Your share of network work, which drives revenue | Which hashrate version is being sold, and the tolerance |
| Power (W) | Wall draw, which sets cost and circuit size | The stated tolerance and test temperature |
| Efficiency (J/TH) | Watts ÷ TH/s. Lower means less electricity per unit of hashrate | Recompute it. 3,500 ÷ 200 = 17.5 J/TH |
| Voltage and phase | Whether it runs on your supply | Single-phase or three-phase, and the range |
| Cooling | Air, hydro or immersion | The extra equipment it implies |
| Condition | New, refurbished, used grade or for parts | For used units, tested hashrate and repair history |
| Availability | Whether the unit exists and where | See the list below |
| Power supply | Whether the PSU and power cords are included | Connector type for your outlet or PDU |
| Warranty | Who stands behind the unit and from what date | The terms in writing |
| Spec source | Where the numbers came from | A link to the manufacturer's page |
Hashrate and power are typical values. Bitmain's listing for the Antminer S21 states that hashrate can vary by ±3% and power by ±5%. A unit running slightly under its label is within specification.
Availability terms mean different things, and the difference is where your money sits while you wait:
- In stock or limited stock means the units are physically held and can be dispatched.
- Incoming means they are in transit to the seller.
- Available to source means the seller does not hold them and will procure them after you order.
- Futures or preorder means they come from a future production batch, and delivery depends on the manufacturer's schedule.
- Availability on request means nothing is confirmed. Ask.
Sourced and futures orders are legitimate, but you are paying before the goods are in the seller's hands. Get the delivery estimate and the refund terms for a slipped batch in writing.
Vet the seller and pay safely
The ASIC market has real fraud. The common patterns are impersonation of a genuine distributor through a lookalike domain or a cloned messaging account, payment details that change mid-deal, and stock that does not exist.
- Reach the seller yourself. Type the domain by hand. Compare it character by character with the email address and the invoice. Use contact details from the seller's own site, such as its verification page, not from the message that reached you.
- Confirm the legal entity. Look the company up in the official business registry of the country it claims. The registered name, the name on the invoice and the bank account beneficiary should match.
- Ask for proof of these goods. Request a video of the actual units showing the serial number labels and a sheet of paper with today's date and your name. Catalogue photos prove nothing.
- Get a proforma invoice. It should state model, hashrate version, condition, quantity, unit price, delivery term, estimated dispatch, warranty terms and what happens if delivery fails.
- Verify payment details on a second channel. Call a number from the official site and read back the bank details or wallet address. A message announcing new bank details or a different wallet is a well-known route to loss. Stop and call. Compare with the seller's published payment information.
- Treat crypto as final. A wire is hard to reverse and a crypto transfer cannot be reversed. Confirm the network as well as the address, since USDT exists on several networks. For a large amount, send a small test payment, have receipt confirmed, then send the balance to the same address.
- Distrust the outlier. A price far below every other quote for a current model, combined with pressure to pay within hours, is a warning and not a bargain.
After you order
- Confirm the delivery term. Ask who pays freight, insurance, import duty and tax, and who deals with customs. Charges at the border depend on your country. How to Import Bitcoin Miners explains the roles.
- Track the shipment and answer the carrier or customs broker promptly. Unanswered clearance requests lead to storage charges.
- Inspect before signing. Look for crushed corners, punctures and water marks. Write any damage on the delivery receipt and photograph it.
- Film the unboxing, including the serial number label.
- Let a cold unit warm up to room temperature before powering it, so condensation does not form on the boards.
- Look and listen without opening it. Check through the fan grilles for loose parts and listen for rattling when you move the unit gently. Opening a machine can affect its warranty.
- Run it. On the correct circuit, connect Ethernet, set your pool and let it run for at least a day. Check that average hashrate is within tolerance of the listing, every hashboard and fan is reporting, and temperatures are steady.
- Report faults inside the window. Dead on arrival (DOA) means the unit does not work correctly when first powered. Send the seller your video, the status page and the log before the stated deadline.