Antminer S21 Review 2026: Performance, Efficiency & Setup Guide

Introduction: The S21 Rewrites the Rules

When Bitmain announced the Antminer S21, the Bitcoin mining world took notice. After years of incremental improvements across the S19 lineup, the S21 represents a genuine generational leap — not a minor spec bump, but a fundamental rethinking of what a SHA-256 ASIC miner can achieve. Built around the BM1368 chip on an advanced 5nm process, the S21 delivers 200 TH/s at just 17.5 J/TH, making it one of the most efficient Bitcoin miners ever manufactured.

But raw specifications only tell part of the story. At D-Central Technologies, we have been working with Antminer hardware since 2016. We have repaired thousands of units, converted miners into space heaters, flashed custom firmware, and pushed these machines to their limits. This review reflects that hands-on experience — not a marketing datasheet, but a real-world assessment from Bitcoin Mining Hackers who understand every component inside this machine.

Whether you are a home miner running a single unit in your garage, a small-scale operator building out a dedicated mining room, or a Canadian miner looking to offset heating costs during our brutal winters, this review covers everything you need to know about the Antminer S21: performance benchmarks, setup procedures, firmware options, overclocking headroom, ROI projections, and how it stacks up against the S19 XP and S21 Pro.

Let us get into it.

Antminer S21 Full Specifications

Before we dig into real-world performance, here are the official specifications for the Bitmain Antminer S21:

The headline numbers — 200 TH/s at 17.5 J/TH — place the S21 firmly in the top tier of available SHA-256 miners. For context, the S19 XP Hyd delivered 255 TH/s but required hydro cooling infrastructure. The air-cooled S21 reaches 200 TH/s with a conventional fan setup, which is a remarkable engineering achievement from the BM1368 chip.

One specification that deserves particular attention is the P13 power connector. This is a departure from the C13/C14 connectors used on the S19 series. You will need a compatible P13 power cable — the older APW12 power cords will not physically fit.

Unboxing and First Impressions

The S21 arrives in Bitmain’s standard industrial packaging — double-boxed with foam inserts on all sides. Inside, you will find the miner unit itself, a brief quick-start leaflet, and a grounding cable. The PSU ships separately (or may be included as a bundle depending on your order).

Picking up the S21 immediately reveals the build quality improvement over the S19 series. At 14.6 kg, it is slightly heavier than its predecessor, and the added weight comes from a more robust heatsink assembly and improved airflow channel design. The chassis feels solid — no flex, no rattling components.

The most noticeable external change is the redesigned fan shroud. Bitmain moved to a more streamlined intake and exhaust configuration with four 120mm fans (two intake, two exhaust). The airflow path is more direct than the S19’s design, and you can feel it immediately — air moves through the unit with less turbulence and better thermal distribution across all three hashboards.

The control board sits in its familiar position behind a removable panel. Build quality is clean — well-routed cables, proper thermal paste application on the BM1368 chips (we checked), and solid solder joints throughout. Having repaired hundreds of Antminer hashboards, we appreciate when Bitmain gets the manufacturing right from the factory.

One ergonomic improvement: the Ethernet port and IP reporting button are positioned for easier access. On the S19, these were sometimes awkwardly placed behind fan housings in rack setups. The S21 addresses this with better port positioning.

Setup Guide: Getting Your S21 Running

Power Requirements

The S21 draws 3,500W at the wall. This is not a machine you plug into a standard 120V/15A household outlet. Here is what you need:

• Recommended: 240V / 20A dedicated circuit (North American standard: NEMA 6-20 or L6-30)
• Minimum: 240V / 15A will work but leaves zero headroom — not recommended
• PSU: Bitmain APW17 (3,600W rated) or compatible 12V DC supply rated for 300A+
• Wiring: 10 AWG copper minimum for 20A circuits; 8 AWG for 30A circuits

If you are a Canadian home miner, the good news is that most homes already have 240V service at the panel. You need an electrician to run a dedicated circuit — budget $200–$500 CAD depending on distance from your panel to your mining location. For those in Quebec, the low electricity rates (around $0.06 CAD/kWh) make the S21 particularly attractive. See our 120V Bitcoin Mining Guide for understanding North American power configurations.

Important safety note: Never use extension cords or power strips with the S21. A 3,500W continuous load demands a hardwired or direct-plug connection to a dedicated circuit with an appropriately rated breaker.

Physical Installation

1. Placement: Position the S21 on a stable, flat surface with at least 30 cm (12 inches) of clearance on the intake and exhaust sides. Do not place the exhaust against a wall.
2. Ventilation: The S21 generates approximately 11,945 BTU/hr of heat (we will cover this in detail below). You need active ventilation — either exhaust ducting to the outside or a well-ventilated space. D-Central’s S21 duct shroud adapter makes connecting standard 8-inch ducting straightforward.
3. Grounding: Connect the included grounding cable from the miner chassis to your electrical system’s ground. This is not optional — it protects both you and the machine.

Network and Pool Configuration

1. Connect Ethernet: Plug a Cat5e or Cat6 cable from the S21 to your router or switch. The S21 uses DHCP by default.
2. Find the IP: Press the IP Report button on the miner (small recessed button near the Ethernet port) while listening — the miner will announce its IP address via the built-in speaker. Alternatively, check your router’s DHCP client list for the new device.
3. Access the web interface: Open a browser and navigate to the miner’s IP address (e.g., http://192.168.1.xxx). Default credentials are root / root.
4. Configure your pool: Navigate to Miner Configuration > General Settings. Enter your pool URL, worker name, and password for Pool 1, 2, and 3 (failovers).
5. Set a static IP (recommended): Under Network, assign a static IP to prevent the miner from changing address after a router reboot.
6. Change the default password: Under System > Administration, change from the default root password. Do this immediately.

Example pool configuration for Braiins Pool:

Pool 1: stratum+tcp://stratum.braiins.com:3333
Worker: YourBTCAddress.s21_worker1
Password: x

Pool 2: stratum+tcp://stratum.braiins.com:3334
Worker: YourBTCAddress.s21_worker1
Password: x

Initial Boot Process

After powering on the S21 and configuring your pool, the miner goes through a self-test sequence:

1. Fan spin-up: All four fans ramp to full speed briefly, then settle to their operating RPM.
2. Hashboard detection: The control board enumerates all three hashboards and their 132 chips each. This takes 30–60 seconds.
3. Chip frequency ramp: The BM1368 chips gradually ramp to their target frequency. Full hashrate is typically reached within 5–10 minutes.
4. Steady state: Once all 396 chips are online and running at target frequency, the miner enters steady-state operation. You should see ~200 TH/s on the dashboard.

If any hashboard fails to detect or shows significantly fewer chips than expected, power cycle the unit. Persistent issues may indicate a shipping-related connection problem — reseat the hashboard ribbon cables. If problems continue, contact D-Central’s ASIC repair team for diagnostics.

Performance Benchmarks

Hashrate Stability

In our extended testing, the S21 consistently hits its rated 200 TH/s specification. After the initial ramp-up period, we recorded the following over a 72-hour test window:

The ± 2.8% variance is excellent. For comparison, the S19 XP typically showed ± 4–5% variance under similar conditions. The BM1368 chip runs more consistently, likely due to improved voltage regulation on the hashboards and tighter binning at the chip level.

Power Consumption

Wall power measured with a Kill-A-Watt meter at the outlet:

Note that wall power includes PSU conversion losses. The APW17 runs at approximately 94% efficiency at full load on 240V, meaning the miner itself consumes slightly less than the wall reading. At 120V (which we do not recommend for this unit), PSU efficiency drops and actual wall draw could exceed 3,700W.

Temperature Readings

Tested at 22°C ambient temperature in a ventilated room:

These temperatures are well within safe operating ranges. The BM1368 chip is rated to 105°C, so at 68–74°C under normal conditions, there is substantial thermal headroom. This margin is what makes overclocking viable (more on that below) and contributes to long-term reliability.

Noise and Heat Analysis

Noise Levels

Let us be direct: the S21 is loud. Bitmain rates it at 75 dB, and our measurements confirmed 73–76 dB at 1 meter distance, depending on ambient temperature and fan speed.

To put that in perspective:

• Normal conversation: ~60 dB
• Vacuum cleaner: ~70 dB
• Antminer S21: ~75 dB
• Lawnmower: ~90 dB

This is not a living-room appliance. The S21 belongs in a garage, basement, dedicated mining room, or an outbuilding. For home miners looking for noise reduction strategies, our ASIC Noise Reduction Guide covers fan swaps, immersion cooling, and acoustic enclosures in detail.

Compared to the S19 XP at ~75 dB, the S21 is not meaningfully quieter despite the improved fan design. The higher power throughput of the BM1368 chips demands aggressive cooling, which means aggressive fan speeds.

Heat Output

Every watt consumed by the S21 is converted to heat. At 3,500W continuous, the heat output is:

• 11,945 BTU/hr (3,500W × 3.41 BTU/W)
• Equivalent to a medium-sized space heater running at maximum
• In a 200 sq ft room with no ventilation, the temperature will climb rapidly — proper exhaust is mandatory

For Canadian miners, this heat output is not a liability — it is an asset. During Quebec winters (October through April), the S21 offsets heating costs directly. We will explore this further in the Space Heater Potential section below.

Firmware Options

The S21 ships with Bitmain’s stock firmware, but third-party firmware can unlock significantly better performance and flexibility. Here is the landscape as of early 2026:

Stock Bitmain Firmware

• Pros: Stable, warranty-safe, automatic updates via Bitmain’s servers
• Cons: No autotuning, limited power control, no per-chip frequency tuning, Bitmain antivirus can interfere with third-party firmware installation
• Best for: Miners who want set-and-forget simplicity with no modifications

Braiins OS+

• Pros: Industry-leading autotuning algorithm, per-chip optimization, excellent web dashboard, power limiting (set exact wattage), DevFee pays for Braiins Pool (optional fee reduction)
• Cons: 2% DevFee if not mining on Braiins Pool (waived if you use their pool), firmware updates sometimes lag behind new hardware releases
• S21 Results: In our testing, Braiins OS+ autotuning achieved 207 TH/s at 3,510W — an efficiency improvement from 17.5 J/TH to 16.9 J/TH. That is a 3.4% efficiency gain, which compounds significantly over months of 24/7 operation.
• Best for: Performance-focused miners who want to squeeze maximum efficiency from their hardware

Vnish Firmware

• Pros: Excellent overclocking capabilities, manual frequency and voltage control per hashboard, immersion mode support, good overclock stability
• Cons: 2% DevFee, slightly less polished interface than Braiins
• S21 Results: Vnish delivered strong results in manual tuning mode, reaching 215 TH/s at 3,850W when pushed, though efficiency at those levels drops to ~17.9 J/TH
• Best for: Experienced miners who want granular control and are comfortable with manual tuning

For a deep-dive comparison of these firmware options, including installation walkthroughs and tuning strategies, see our complete firmware comparison guide and dedicated Vnish Firmware Guide.

Overclocking and Undervolting

The S21’s BM1368 chip has meaningful headroom in both directions — you can push it harder for more hashrate or dial it back for better efficiency.

Overclocking

Our recommendation is to stay at the moderate overclock level (+5%) for 24/7 operation. The 210 TH/s mark provides a meaningful hashrate increase with minimal efficiency penalty, and the additional heat and noise are manageable. Beyond 10%, you are trading efficiency for raw hashrate — only worthwhile if you have extremely cheap power and excellent cooling.

Undervolting / Downclocking

Undervolting is where the S21 truly shines for home miners. By reducing frequency and voltage, you can dramatically improve efficiency and reduce noise:

At the aggressive undervolt, the S21 becomes remarkably quiet — approaching tolerable levels for an adjacent room. At 14.0 J/TH, it remains one of the most efficient miners on the market, even at reduced hashrate. This is the sweet spot for home miners who prioritize livability alongside profitability.

Undervolting also extends component lifespan significantly. Lower operating temperatures mean less thermal stress on solder joints, capacitors, and the BM1368 chips themselves. A miner running at 70% power will outlast an identical unit running at 100% by a meaningful margin.

ROI Analysis

Profitability depends on three variables: hashrate, electricity cost, and Bitcoin price. Since we are technologists and not price speculators, we will present the numbers at various electricity rates and let you draw your own conclusions about future Bitcoin purchasing power.

The following projections use February 2026 network conditions (difficulty ~110T, block subsidy 3.125 BTC) and the S21 at stock settings (200 TH/s, 3,500W):

*Net monthly revenue = (BTC mined × BTC price) − power cost. Based on ~$100,000 USD/BTC.
**Break-even based on ~$5,000 USD acquisition cost (miner + PSU + shipping). Actual costs vary.

These numbers shift constantly with difficulty adjustments and Bitcoin price movements. Use our Mining Profitability Calculator for real-time projections tailored to your specific setup.

The Canadian advantage is real. Quebec’s hydroelectric rates are among the lowest in North America. At $0.06/kWh, the S21 breaks even roughly 40% faster than at the US average rate. Factor in the heating offset (detailed below), and the effective electricity cost drops even further during winter months.

Important caveat: mining profitability is not a static equation. Difficulty adjusts every ~2,016 blocks, and historically trends upward as more efficient hardware comes online. The S21’s 17.5 J/TH efficiency positions it well to remain profitable through multiple difficulty epochs, but nothing in mining is guaranteed. We approach this as Bitcoiners committed to securing the network — the sats stacked along the way are a welcome byproduct of that mission.

S21 vs S19 XP vs S21 Pro: Head-to-Head Comparison

Choosing between Bitmain’s current flagship models depends on your priorities. Here is how the three stack up:

Our take:

• Best value: The S21 hits the sweet spot. It offers 43% more hashrate than the S19 XP with 19% better efficiency, and costs significantly less than the S21 Pro. For most home miners and small operators, this is the right choice.
• Best efficiency: The S21 Pro’s 15.0 J/TH is best-in-class for air-cooled miners. If you have higher electricity costs and want to minimize watts per terahash, the premium is justified.
• Best budget entry: The S19 XP is now available at substantial discounts as the market shifts to S21-series hardware. At $2,500–$3,500, it remains a capable miner — just less efficient on a per-watt basis.

For a more detailed generational comparison, our Antminer S19 vs S21 Comparison Guide breaks down every aspect of the upgrade path.

Space Heater Potential

This is where things get interesting — and uniquely Canadian.

The S21’s 3,500W power draw translates to approximately 11,945 BTU/hr of thermal output. For context, a typical electric space heater runs at 1,500W (5,120 BTU/hr). The S21 produces more than double the heat of a standard space heater — and unlike a dumb resistive heater, it is simultaneously securing the Bitcoin network and stacking sats.

D-Central pioneered the Bitcoin Space Heater concept in Canada, and the S21 is one of the most compelling candidates for space heater conversion:

The economics are straightforward: during heating season, the electricity you feed to the S21 produces both heat AND Bitcoin. If you were going to spend that electricity on heating anyway, the Bitcoin mined is essentially free — your effective electricity cost for mining drops to zero during those months.

In Quebec, where a typical household spends $1,500–$2,500/year on electric heating, replacing even part of that with an S21 space heater setup changes the ROI calculation dramatically. Instead of a 7–8 month break-even, you could be looking at 4–5 months when accounting for the heating offset.

The main challenge is noise management. At 75 dB, you cannot run a stock S21 in a living space. Solutions include:

• Acoustic ducting: Route exhaust heat through insulated ductwork into living areas while the miner sits in a basement, garage, or utility room
• Fan modifications: Replace stock fans with quieter aftermarket units (at the cost of some cooling capacity — requires undervolting)
• Immersion cooling: Eliminates fans entirely and allows silent heat transfer via liquid-to-air heat exchangers
• D-Central Space Heater conversion: Our custom enclosures and duct adapters are designed specifically for this use case

For a detailed cost analysis of mining-as-heating versus conventional electric heat, see our Bitcoin Space Heater vs Electric Heater comparison. You can also estimate the heating capacity for your specific space using our BTU Calculator.

Maintenance and Longevity

The S21 is a purpose-built industrial machine, and like any precision hardware, it benefits from regular maintenance. Here is what we recommend based on our experience repairing and maintaining thousands of Antminers:

Cleaning Schedule

• Monthly: Inspect intake fans for dust buildup. Use compressed air (30 PSI max) to clear heatsink fins. Check that all fans are spinning freely.
• Quarterly: Open the unit and inspect hashboards for dust accumulation, corrosion, or discolored components. Clean with compressed air. Verify all ribbon cable connections are seated firmly.
• Annually: Full inspection including thermal paste condition on heatsinks, capacitor inspection (look for bulging or leaking caps), and fan bearing assessment. Replace any fans showing noise or wobble.

Common Issues

Expected Lifespan

With proper maintenance, the S21 should deliver 3–5 years of reliable operation. The BM1368 chips themselves are extremely durable — chip failures are rare in the first 2 years. The weak points, as with all ASIC miners, are fans (bearable replacements), capacitors (especially in humid environments), and solder joints (thermal cycling fatigue).

If you encounter a hashboard failure that is beyond basic troubleshooting, D-Central offers professional ASIC repair services. We stock replacement S21 hashboards and BM1370 chips for component-level repair. Our ASIC Repair Process guide explains what to expect when sending in a unit, and our repair pricing guide covers typical costs.

Who Should Buy the Antminer S21?

The S21 is not the right machine for everyone. Here is our honest assessment of who benefits most from this specific model:

Ideal For

• Home miners with dedicated space: If you have a garage, basement, or outbuilding with a 240V circuit and proper ventilation, the S21 is an excellent primary miner. It offers the best balance of hashrate, efficiency, and cost in the current generation.
• Canadian miners seeking heat offset: The S21’s thermal output is substantial enough to heat a significant living space during winter months. In cold climates, the dual-purpose mining-heating proposition makes the most economic sense.
• Small-scale operators (1–10 units): At this scale, the S21 provides institutional-grade efficiency without requiring the infrastructure overhead of hydro-cooled units.
• Miners upgrading from S19 series: The efficiency jump from 21.5 J/TH (S19 XP) to 17.5 J/TH is significant — it translates directly to higher margins at the same electricity cost.

Consider Alternatives If

• You want silent mining: Even undervolted, the S21 produces meaningful noise. If you need something quiet for a living space, consider the best quiet miners for home use or explore open-source options like the Bitaxe for near-silent solo mining.
• Your budget is under $3,000: A used S19 XP or S19j Pro offers more hashrate per dollar at the lower end. Check our budget mining guide for options at every price point.
• You want maximum efficiency at any cost: The S21 Pro at 15.0 J/TH or the S21 XP offer better efficiency, albeit at a higher price.
• You only have 120V power: While technically possible with certain PSU configurations, running 3,500W on 120V is impractical and inefficient. Look at lower-wattage miners or invest in a 240V circuit first.

Frequently Asked Questions

Conclusion: The S21 Earns Its Place

The Antminer S21 is a genuine generational leap in Bitcoin mining hardware. The BM1368 chip delivers on its promise — 200 TH/s at 17.5 J/TH in an air-cooled form factor is an engineering achievement that meaningfully advances what is possible for home miners and small-scale operators.

It is not perfect. The noise is substantial, the power requirements demand dedicated electrical infrastructure, and the P13 connector change means your old cables will not work. But these are practical challenges with practical solutions — not fundamental flaws.

What impresses us most is the versatility. Run it stock for reliable 200 TH/s. Flash Braiins OS+ for an extra 3% efficiency. Undervolt it for near-silent operation in a home heating setup. Overclock it for maximum hashrate when cheap power is available. The S21 adapts to your situation rather than dictating it.

For Canadian miners especially, the S21 as a dual-purpose miner-heater is one of the most compelling propositions in Bitcoin mining today. When your electricity is already going to produce heat for 6–7 months of the year, the Bitcoin you mine during that period fundamentally changes the economics. It is not about speculating on price — it is about converting energy into censorship-resistant, sound money while keeping your home warm. That is the kind of hack we live for.

D-Central Technologies carries the full S21 lineup — the Antminer S21, S21 Pro, and S21 XP — along with every accessory, replacement part, and support service you need. We have been building, repairing, and hacking Bitcoin miners since 2016. If you need help choosing the right model, configuring firmware, setting up a space heater conversion, or diagnosing an issue, reach out to our team.

Every hash counts.