Antminer S21+ 216T Review: Specs and Power Draw

The Antminer S21+ ships rated 216 TH/s, 3,564 W at the wall, 16.5 J/TH efficiency, SHA-256 algorithm, air cooling. Those four numbers — hashrate, wall draw, efficiency and cooling method — decide everything else: what circuit you need, how much heat the room absorbs, and how the machine behaves when network difficulty climbs. Everything a spec sheet lists beyond that is packaging.

Treat the rated figures as a ceiling rather than a promise. Air-cooled units typically settle two to five percent below datasheet output once intake air passes 30 degrees Celsius, while liquid-cooled siblings hold their numbers far more consistently. We bench every Antminer S21+ before it ships and record the actual hashrate and wall draw on the test sheet that travels with the unit.

Efficiency (16.5 J/TH) is what determines survival through difficulty growth. Machines above roughly 30 J/TH are cash-flow plays for operators with very cheap or curtailed power. Units between 18 and 28 J/TH are the value tier. Anything under 16 J/TH is current-generation hardware you can plan a multi-year deployment around.

The S21+ is a modest refresh of the S21 with slightly better efficiency at 16.5 J/TH. Compare the Antminer S21+ against alternatives on delivered price per terahash next to efficiency: paying more per terahash is only rational when the extra capital buys materially lower energy draw for the same output.

At 3,564 W continuous the Antminer S21+ consumes roughly 86 kWh per day. At six cents per kilowatt hour that is about $5 of power per day; at twelve cents it doubles to roughly $10. Multiply by 30 and you have the only fixed cost that never negotiates.

Because power is the dominant cost, your electricity rate — not the purchase price — decides whether this machine belongs in your fleet. Run the numbers with hashprice cut by 30 percent before you buy. If the Antminer S21+ still clears its own power bill in that stressed scenario, the purchase survives a bad quarter; if it does not, you are betting on price appreciation rather than on mining.

An air-cooled Antminer S21+ produces 72 to 80 dB continuously and dumps its entire 3.6 kW into the room as heat. That rules out living spaces without a garage, outbuilding, ducted enclosure or hosting contract. Noise, not electricity, is the reason most home mining purchases get resold within a month.

Whatever the cooling method, intake temperature is the metric to instrument. Log intake, exhaust and chip temperatures, alarm on 75 degrees Celsius chip temperature, and clean filters on a fixed schedule. Thermal discipline is the difference between a five-year machine and an eighteen-month one.

Keep firmware on a known-good stock release unless you have a specific reason to change. Vendor firmware includes thermal protections that custom builds sometimes relax, and a machine that hashes five percent faster while running ten degrees hotter is a bad trade over three years. Take a config backup before any flash, and never flash a fleet without testing one unit first.

Point the Antminer S21+ at two or three pools in priority order so a pool outage does not cost you a day of hashrate. Set worker names per machine, monitor accepted versus rejected shares, and alarm on any unit that drops below 95 percent of its benchmarked hashrate — that is usually a failing hashboard long before it fails outright.

Compare with the S21 Pro at 15 J/TH — often the better buy per delivered terahash. Do not compare on headline hashrate alone; two machines with the same output can differ by 40 percent in electricity cost, which is the entire margin at most power rates.

Our sales desk will model two or three candidates against your actual electricity rate, available amperage and budget, then quote delivered pricing so you can compare like with like. That takes an afternoon of spreadsheet work off your plate and usually changes the shortlist.