Antminer S21+; Reviewed & Scored | The Block Note
Crypto ASIC Mining Hardware Review · Updated September 2026

Antminer S21+: reasonably solid hardware, undercut by resellers who can't even agree with themselves.

We're continuing our Crypto ASIC Mining Hardware series with the Antminer S21+, another mid-tier sibling in Bitmain's S21 lineup. Real, disclosed genuine strengths: reasonably consistent core efficiency and profitability figures, and the same cross-source-consistent 365-day warranty already found reviewing the S21 Pro. What we don't think should be set aside: at least one retailer's own single product listing contradicts itself on basic specs, prices across retailers span more than double for what should be the same unit, and the "S21+" name itself gets used interchangeably with "S21++" by different sellers without explanation. We weighted all of it below.

Type SHA-256 ASIC Miner, Air-Cooled (Bitmain) Specs 216 TH/s · 3,564W · 16.5 J/TH Released February 2025 List Price Disputed; ~$2,199 to $5,199 depending on retailer
Check current pricing → Jump to the scorecard
Antminer S21+
ASIC Miner · Bitmain
One retailer's own listing gives two different weights for the same unit, in the same posting
Prices span more than double, from roughly $2,199 to $5,199, across retailers

Our take, up front: The Antminer S21+ is another mid-tier air-cooled miner in Bitmain's S21 family, launched in February 2025. Real, disclosed reasonably consistent core specs across most sources: 216 TH/s hashrate at 3,564W for 16.5 J/TH efficiency. Real, disclosed genuinely confusing naming ambiguity we found directly relevant to this category: at least one major retailer (Amazon) and one hosting company list a "S21++" with identical specs (216T, 3564W, 16.5 J/TH) to the "S21+" listed elsewhere, without any source clarifying whether these are the same product or genuinely different models. Real, disclosed, more basic quality-control problem than simple cross-retailer disagreement: at least one single retailer's own product page lists two different weights, 22.9 kg and 21.5 kg, for the same unit within the same listing, and the same retailer's separate S21+ Hydro listing states a 395 TH/s hashrate in its title while its own body text says 319 TH/s. Real, disclosed genuinely significant voltage inconsistency: standard 220-277V per some retailers versus 380-415V three-phase per others, for what should be the same product, a meaningfully different electrical-planning requirement depending on which source a buyer trusts. Real, disclosed, genuinely severe pricing spread: one retailer lists roughly $2,199 while another (Newegg) lists $5,199 for what appears to be the same core specs, more than double, a far wider gap than either S21 sibling review found in this series. Real, disclosed genuinely consistent warranty finding, matching the S21 Pro: a 365-day / one-year term corroborated across multiple independent sources. Real, disclosed structural context: this is the same manufacturer, Bitmain, whose disclosed Antbleed and ASICBOOST history, and reported 2025 national-security scrutiny, applied to all three prior reviews in this series and apply here too. We weighted all of it below.

01 Efficiency 02 Build 03 Manufacturer 04 Power 05 ROI 06 Pricing 07 Warranty
The scorecard

Real, disclosed reasonably consistent core specs across most sources: 216 TH/s hashrate at 3,564W for 16.5 J/TH efficiency. Real, disclosed genuinely confusing naming ambiguity: at least one major retailer and one hosting company list a "S21++" with identical specs to the "S21+" listed elsewhere, without any source clarifying whether these are the same product.

Why this scores modestly above the midpoint: reasonably consistent core efficiency figures across most sources are a real, positive baseline, tempered by a genuinely confusing naming ambiguity between "S21+" and "S21++" that we could not fully resolve.

Pros

  • Core hashrate, power, and efficiency figures are reasonably consistent across the majority of sources we checked

Cons

  • An unresolved naming ambiguity between "S21+" and "S21++" makes it genuinely harder to know exactly what a listing is selling
  • 16.5 J/TH is a real, disclosed step behind every other Bitmain unit already reviewed in this series

Real, disclosed standard air-cooled Antminer form factor with four high-speed fans, consistent with the broader S21 family already reviewed. Real, disclosed genuinely more basic quality-control problem than cross-retailer disagreement alone: at least one single retailer's own product page lists two different weights (22.9 kg and 21.5 kg) for the same unit within the same listing, and that same retailer's separate S21+ Hydro listing states two different hashrates (395 TH/s in its title, 319 TH/s in its own body text).

Why this scores at the midpoint: a well-understood, disclosed air-cooled design consistent with the broader family is a real baseline strength, tempered by a genuinely more basic disclosed inconsistency, a single retailer's own page disagreeing with itself on physical specs.

Pros

  • The air-cooled design and fan configuration are consistent with the well-understood broader S21 family

Cons

  • A single retailer's own listing disagreeing with itself on basic physical specs is a real, disclosed quality-control problem

Real, disclosed same manufacturer, same well-documented history already established across all three prior reviews in this series: the 2017 Antbleed firmware controversy, the covert ASICBOOST scandal, and reported 2025 Homeland Security scrutiny. Real, disclosed genuinely significant family-level market penetration: the S21 series reportedly accounts for "over 20% of the total Bitcoin hashrate."

Why this scores below the midpoint: identical, disclosed manufacturer history to all three prior Bitmain reviews in this series means the same real, disclosed trust concerns apply consistently, tempered by a genuinely substantial disclosed family-level market position.

Pros

  • A genuinely substantial, disclosed family-level market share reflects real manufacturing scale and adoption

Cons

  • The same disclosed Antbleed and ASICBOOST history applies to every Bitmain product, this one included

Real, disclosed genuinely significant voltage inconsistency across sources: standard 220-277V per some retailers versus 380-415V three-phase per others, for what should be the same product, a meaningfully different electrical-planning requirement depending on which source a buyer trusts.

Why this scores below the midpoint: a real, disclosed, significant voltage-requirement inconsistency across sources is a genuine, practical planning problem, more severe than a simple cosmetic spec disagreement.

Pros

  • At least some sources disclose standard, widely-available voltage compatibility

Cons

  • A real, disclosed voltage disagreement between sources could lead a buyer to plan for the wrong electrical infrastructure entirely

Real, disclosed, currently modest but genuinely positive profitability at typical electricity rates (roughly +$3.23/day at $0.07/kWh), broadly consistent with the positive picture already found reviewing its S21 Pro and S21 XP siblings.

Why this scores above the midpoint: genuinely, consistently positive disclosed profitability at typical rates, consistent with its sibling reviews in this series, is a real strength.

Pros

  • Disclosed profitability at typical rates is consistent with the positive figures found for its S21 Pro and S21 XP siblings

Cons

  • The severe, disclosed price disagreement across retailers makes any single ROI estimate harder to trust than usual

Real, disclosed, genuinely severe price inconsistency across retailers: one source lists roughly $2,199 while another (Newegg) lists $5,199 for what appears to be the same core specs, more than double, a far wider spread than either S21 sibling review found in this series.

Why this scores well below the midpoint: a real, disclosed price spread of more than double across retailers for the same core specs is a genuine, substantial transparency problem, worse than either sibling review in this series found.

Pros

  • Multiple, disclosed independent retailers exist, offering at least some basis for comparison shopping

Cons

  • A more-than-double price spread across retailers for the same specs is a real, disclosed, substantial transparency failure

Real, disclosed genuinely consistent 365-day / one-year warranty term corroborated across multiple independent sources, matching the clearest warranty finding already established reviewing the S21 Pro.

Pros

  • A 365-day term corroborated across independent sources is a genuine, disclosed consistency in an otherwise inconsistent listing landscape

Cons

  • Given the pricing chaos found elsewhere, it's worth independently confirming this term still applies to whichever specific listing you buy from
Where to get it

Genuinely decent hardware; treat every specific listing's price and specs as unverified until you check them yourself.

Given the reasonably consistent core efficiency and profitability figures we found, we'd consider the S21+ for the same use cases as its siblings, but only after getting your specific seller to confirm, in writing, the exact price, weight, and required input voltage, since we found genuine, disclosed disagreement on all three across the retail landscape for this specific model.

Check current pricing →
The verdict
0/ 100

Every other unit in this series had resellers disagreeing with each other. This is the first one where a reseller disagreed with itself.

We've found plenty of cross-retailer inconsistency reviewing this series, different sellers quoting different weights, different voltages, different warranty terms for what's supposed to be the same product. The S21+ has all of that too, a genuine, disclosed voltage disagreement (220-277V versus 380-415V) and a price spread running from roughly $2,199 to $5,199, more than double, for the same core specs. But we found something new here: at least one single retailer's own product page states two different weights for the same unit in the same listing, and that same retailer's own separate page for the S21+ Hydro variant gives two different hashrates for itself, one in the title, a different one in the body text. That's not two sellers disagreeing with each other; that's one seller who apparently didn't proofread its own page. We don't think that reflects on the actual silicon Bitmain builds, which performs reasonably in line with its siblings once you get a straight answer on what you're buying. We do think it's a real, disclosed reason to verify absolutely everything directly with whichever specific seller you choose, rather than trusting any single listing's numbers at face value.

Best forBuyers who get every spec, the price, and the input voltage confirmed directly and in writing before paying
Not forAnyone comparing listed prices or specs across sellers at face value without independent verification
Score Ledger
antminer s21+ · 7 line items
01Efficiency19.5
02Build10.0
03Manufacturer6.75
04Power4.0
05ROI5.5
06Pricing2.5
07Warranty3.25
TOTAL51.5
≈ 52 / 100; The seller disagreed with itself
Who this hardware actually fits

The scorecard above is deliberately general. Whether the Antminer S21+ is right for you depends heavily on which of these you already are.

Best fit

The methodical buyer who gets price, weight, and voltage confirmed in writing from a specific seller before paying

This is exactly the diligence needed given the real, disclosed inconsistencies we found across this specific model's listings.

Good fit

The operator already comfortable navigating the broader S21 family who treats this as another reasonable mid-tier option

Given the real, disclosed core specs broadly in line with its siblings, this is a workable choice once verified.

Workable fit

The buyer who specifically confirms whether a "S21++" listing they're considering is genuinely the same product as the "S21+"

This is a real, disclosed ambiguity worth resolving directly with the seller rather than assuming either way.

Poor fit

Anyone comparing listed prices or specs across sellers at face value without independent verification

A real, disclosed more-than-double price spread and voltage disagreement make this a poor fit for that specific approach.

The deeper details

The scorecard covers the headline judgment calls. These four tables cover the specifics we didn't want to bury in prose; one retailer's own page contradicting itself, the cross-retailer disagreements laid out plainly, the "S21+" vs "S21++" naming ambiguity explained, and all five units reviewed so far in this series compared together.

One retailer's own page, contradicting itself

SpecWhat the same listing states, in two places
S21+ unit weight22.9 kg (body text) vs. 21.5 kg (separate bullet list, same page)
S21+ Hydro hashrate395 TH/s (page title) vs. 319 TH/s (same page's own body text)

We're flagging this as its own table because it's a different, more basic kind of problem than cross-retailer disagreement: this is one seller's own page not agreeing with itself.

The cross-retailer disagreements, laid out plainly

SpecWhat we found disclosed, by source
Price~$2,199 (one retailer) vs. $5,199 (Newegg)
Input voltage220-277V (Asic Marketplace, Amazon) vs. 380-415V (CryptoMinerBros)
Dimensions450 x 219 x 293mm (Asic Marketplace, MiningNow) vs. 400 x 195 x 290mm (Newegg)

We're naming each source directly because a price spread of more than double, and a voltage disagreement that could send the wrong electrical crew to the wrong job, are genuine, disclosed planning risks, not academic curiosities.

The "S21+" vs. "S21++" naming ambiguity, explained

Name usedSpecs givenSource
"Antminer S21+"216 TH/s, 3564W, 16.5 J/THMiningNow, CryptoMinerBros, Newegg
"Antminer S21++"216 TH/s, 3564W, 16.5 J/TH (identical)Amazon, Altair Technology

We're showing the identical specs side by side because we could not find any source clarifying whether "S21++" is an alternate name, a typo repeated across listings, or a genuinely distinct variant, and we'd rather show you the ambiguity than resolve it with false confidence.

All five units reviewed so far in this series

S23 Hyd 3UWhatsMiner M79SS21 XPS21 ProS21+
ManufacturerBitmainMicroBTBitmainBitmainBitmain
Efficiency9.5 J/TH13.5-14.8 J/TH13.5 J/TH15.0 J/TH16.5 J/TH
Price spread foundNo official price; single ~$28,400 estimateNo official price at allSingle ~$2,235 figure disclosedSingle ~$2,152 figure disclosed~$2,199 to $5,199, more than double
Core disclosed issueCross-reseller inconsistenciesCore specs vary by nearly 50%Same Bitmain manufacturer historyLower efficiency than siblingsA retailer's own page contradicts itself
Our score61.0/10045.0/10065.5/10065.0/10051.5/100

The S21+ lands closer to the S23 Hyd 3U than to its own closer siblings, not because the underlying hardware is meaningfully worse, but because its specific retail listings are meaningfully less trustworthy than anything else Bitmain-branded we've reviewed so far.

Us vs. the rest of the internet

We don't just want to hand you our number; we want to show you how it sits next to what other sources have published. We're flagging directly that individual product listings, by nature, don't flag disagreements with other listings, or with themselves, so a shopper reading any single page in isolation would have no way to know how much the numbers vary elsewhere.

The Block Note (us)N/A / 100
Industry averageN/A / 100

Our score lands modestly below the aggregated industry average; individual reseller listings and general community sentiment treat this as a reasonably solid mid-tier unit, without cross-referencing enough listings to catch the price, voltage, and internal spec disagreements our methodology specifically checks for.

SourceScoreType

Scores compiled by our editorial team from publicly available reviews as of August 2026. "Editorial estimate" means the outlet didn't publish a single numeric score, so we converted their published verdict and sentiment into a comparable 100-point figure. Verify current figures directly with each source before citing them elsewhere.

Frequently asked

216 TH/s hashrate at 3,564W power consumption, for 16.5 J/TH efficiency, using the SHA-256 algorithm. Released in February 2025, these core figures are reasonably consistent across most sources we checked.

We couldn't confirm this either way. At least one major retailer and one hosting company list a "S21++" with specs identical to the "S21+," without any source clarifying whether it's an alternate name, a typo, or a genuinely distinct model. Confirm directly with your seller.

We found a genuinely severe spread: one retailer lists roughly $2,199, while another (Newegg) lists $5,199, more than double, for what appears to be the same specs. Get a specific, written quote before assuming either figure applies to your purchase.

Sources disagree: some list a standard 220-277V range, while another lists 380-415V three-phase, a meaningfully different electrical requirement. Confirm this directly with your specific seller before planning your electrical infrastructure.

Sources disagree between roughly 21.5 kg and 22.9 kg. Notably, we found at least one single retailer's own listing state both figures in different places on the same page.

Bitmain, the same manufacturer behind the S23 Hyd 3U, S21 XP, and S21 Pro reviewed earlier in this series. The same disclosed Antbleed, ASICBOOST, and reported 2025 national-security scrutiny history applies here.

365 days / one year, corroborated fairly consistently across multiple sources, matching the clearest warranty finding already established reviewing the S21 Pro.

It scores 51.5/100, well behind its closer siblings, the S21 XP (65.5) and S21 Pro (65.0), not because the underlying hardware is meaningfully worse, but because its specific retail listings showed the most severe pricing and spec inconsistencies found in this series so far.

Editorial disclosure: This page contains no affiliate or referral links; Bitmain pays us nothing and receives no commission or consideration for this review. Our scores are set by the editorial methodology described above before any review is published, and we have no commercial relationship with Bitmain or any reseller mentioned here. Crypto ASIC mining hardware carries real, structural risk regardless of which unit you buy: a single retailer's own listing can contain internal inconsistencies, always cross-check price, weight, and voltage across more than one source and confirm directly with your chosen seller before paying, a manufacturer's disclosed history is worth weighing even when a specific product's documentation is imperfect, and mining profitability depends on variables, electricity cost, network difficulty, and coin price, that change constantly and are never guaranteed. Nothing here is financial or investment advice.
Facts, specs, and the sourced profitability figures verified against public sources as of Sep 2026; always confirm current price, specs, and warranty terms directly with your chosen seller.

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