Antminer S19 vs S21: Complete Comparison Guide for Home Miners

The Upgrade Decision: Keep Your S19 or Buy an S21?

This is the question that keeps home miners up at night. You are running an S19-series miner — maybe an S19 Pro you bought in 2021, maybe an S19j Pro you picked up used last year, maybe an S19 XP that still feels relatively modern. It is hashing. It is earning sats. It is heating your basement. And then you see Bitmain’s S21 lineup: 200 TH/s at 17.5 J/TH. The S21 Pro at 234 TH/s. The S21 XP at a staggering 270 TH/s and 13.5 J/TH. Numbers that make your S19 look like a relic from a different era of Bitcoin mining.

So do you sell the old machine, eat the depreciation, and buy the new generation? Or do you keep running what you have, stack sats at a lower efficiency, and wait for the next generation to make the S21 look dated?

The answer is not as simple as “newer is better.” It depends on your electricity rate, your available circuits, your heating needs, your budget, your risk tolerance, and your timeline. An S19j Pro at $0.04/kWh in Quebec is a fundamentally different proposition than an S19j Pro at $0.15/kWh in California. An S21 makes sense for a miner building a new operation from scratch but might not justify the capital expenditure for someone who already owns paid-off S19 hardware.

This guide lays out the complete picture. Every specification, every efficiency number, every dollar of electricity cost, every repair consideration, every resale data point. We sell both generations. We repair both generations. We have deployed both generations in our hosting facility in Laval, QC. We are not here to push you toward the more expensive option — we are here to give you the data so you can make the right decision for your situation.

Complete Specifications: Side by Side

Before we analyze anything, you need the raw numbers. The S19 series spans five major variants released between 2020 and 2022, while the S21 series covers three variants released in 2024-2025. The chip generation leap — from BM1398/BM1366 to BM1370 — is the single biggest factor driving the performance gap.

Antminer S19 Series

Antminer S21 Series

The numbers tell a clear story at the silicon level. The S21 series uses the BM1370 chip — Bitmain’s most advanced SHA-256 ASIC — across all three variants. The S19 series spans two chip generations: the older BM1398 (S19, S19 Pro, S19j Pro) and the BM1366 (S19k Pro, S19 XP). The BM1370 achieves roughly 40-60% better efficiency than BM1398-based machines and 19-37% better efficiency than BM1366-based machines. That gap is entirely about semiconductor physics — smaller transistors switching faster at lower voltages.

But specifications alone do not tell you whether to buy one over the other. For that, you need context.

Efficiency Analysis: Joules Per Terahash Explained

Efficiency — measured in joules per terahash (J/TH) — is the single most important number for any miner operating at residential electricity rates. It tells you how much energy your miner consumes to produce one terahash of computational work per second. Lower is better. Always.

Here is why it matters so much: at any given difficulty level and BTC price, every miner on the network earns the same amount of bitcoin per terahash. The only variable you control is how much electricity each terahash costs you. A miner at 17.5 J/TH (S21) uses half the electricity per terahash as a miner at 34.2 J/TH (base S19). Same hashrate contribution to the network, half the electric bill.

Efficiency Comparison: All Variants

The practical impact: if you are running an S19 Pro at 29.5 J/TH and replace it with an S21 at 17.5 J/TH, you get 82% more hashrate (200 vs 110 TH/s) while consuming only 9% more power (3,550W vs 3,250W). That is the magic of a generational chip improvement — dramatically more work per watt.

Hashrate Comparison: Raw Performance in Context

Raw hashrate — measured in terahashes per second (TH/s) — determines your share of the network’s total mining reward. More hashrate means more sats, assuming the same electricity cost per hash. Here is how the two generations stack up in terms of pure computational power.

The jump is massive. A single S21 XP produces nearly as much hashrate as three base S19 units — while drawing only about 12% more power than a single S19. For miners constrained by circuit capacity (which is most home miners), this density advantage is enormous. You can point 270 TH/s at the network from a single 20A 240V circuit instead of needing three circuits for three S19 units.

But context matters. Bitcoin’s network difficulty adjusts every 2,016 blocks (roughly every two weeks) to maintain the ten-minute block interval. As more efficient hardware comes online globally, difficulty rises, and each terahash earns proportionally less bitcoin. The S21’s hashrate advantage is real, but it is competing against a global fleet that is also upgrading. Your share of the network is what determines your income — not your raw TH/s number in isolation.

The S19j Pro at 104 TH/s represented roughly 0.000014% of the network when difficulty was 50T in 2022. Today, with difficulty above 110T, that same machine represents about 0.0000064%. The hashrate did not change — the network grew around it. An S21 at 200 TH/s against today’s difficulty gives you roughly 0.000012% — better, but still a shrinking share as difficulty climbs.

This is why efficiency matters more than raw hashrate for long-term profitability. The machine that survives the next difficulty increase is the one that costs the least to operate per hash.

Power Consumption and Electrical Requirements

Both the S19 and S21 series are hungry machines. They draw between 2,760W and 3,645W at the wall, running 24/7/365. That is not a lamp you plug into a spare outlet. That is a dedicated circuit, a dedicated breaker, and proper wiring. Getting this wrong is how house fires start.

Circuit Requirements by Model

Here is the critical takeaway: both generations require 240V. There is no running an S19 or S21 on a standard 120V/15A household outlet. If you do not already have 240V circuits available (dryer outlet, workshop, EV charger outlet), you will need an electrician to install one. Budget $200-600 CAD depending on your panel capacity and distance to the installation point.

The S21 series draws slightly more power than most S19 variants, but not dramatically more. An S19 Pro at 3,250W versus an S21 at 3,550W is only 300W of difference — roughly the gap between two light bulbs. The S19k Pro is the most electrical-friendly of the entire lineup at 2,760W, drawing only 11.5A at 240V. If your circuits are constrained, the S19k Pro’s efficiency-to-power ratio makes it an interesting value proposition.

Monthly Electricity Cost Comparison

The real number that matters: what does each machine cost you per month in electricity? Here is the math at three representative electricity rates.

At cheap Quebec hydroelectric rates ($0.04/kWh), the monthly electricity cost difference between an S19j Pro and an S21 is only about $14/month. At expensive rates ($0.20/kWh), it is about $70/month. The absolute electricity cost difference between generations is small because the wattage is similar. The S21’s advantage comes from producing far more hashrate per watt — not from drawing less power overall.

Heat Output and Space Heater Potential

Every watt of electricity your miner consumes is converted into heat. This is not a byproduct — it is physics. An ASIC miner is a 100% efficient space heater that also happens to mine bitcoin. A 3,250W S19 Pro produces 11,092 BTU/hr of heat. A 3,550W S21 produces 12,116 BTU/hr. For comparison, a typical portable electric space heater runs at 1,500W (5,118 BTU/hr). Your ASIC miner is two space heaters in one box.

Heat Output by Model

For heating purposes, the S19 and S21 produce nearly identical heat output because they draw nearly identical wattage. The difference is what you get alongside that heat: 200 TH/s of hashrate instead of 95-110 TH/s. The S21 is a better space heater not because it produces more heat — it does not, meaningfully — but because it mines significantly more bitcoin while heating the same room.

That said, if you are buying hardware primarily for heating, the used S19 market offers dramatically better value. A used S19j Pro can be purchased for a fraction of an S21’s price, produces nearly the same heat, and mines enough bitcoin to meaningfully offset (or fully offset, at cheap electricity rates) the energy cost. We built the D-Central Bitcoin Space Heater line on this exact principle — repurposing older-generation ASICs as dual-purpose heating and mining appliances.

Noise Levels: Living with Your Miner

On paper, both the S19 and S21 series are rated at approximately 75 dB at stock settings. That is roughly the volume of a vacuum cleaner running continuously. In practice, the actual noise level depends on ambient temperature, firmware settings, fan condition, and whether you are running at stock or undervolted.

Real-World Noise Expectations

A critical difference: the S19 series has far more third-party firmware options for noise reduction. Braiins OS+, VNish, and LuxOS all support aggressive undervolting and fan curve customization on S19 models, allowing you to cut fan speed dramatically at the cost of some hashrate. The S21, being newer, has fewer aftermarket firmware options as of early 2026. This matters enormously for home miners who need to manage noise levels for daily livability.

If quiet operation is your top priority, the S19j Pro on Braiins OS+ undervolted to 60-70% power is currently the best option for a balance of hashrate, heat, and noise that a human can coexist with. The S21 will get there as firmware support matures, but it is not there yet.

Profitability Analysis: The Numbers That Matter

This is the section everyone skips to. Fair enough. Let us run the numbers.

Mining profitability depends on four variables: hashrate, electricity cost, network difficulty, and BTC price. We cannot predict the future of difficulty or BTC price, so we will calculate what each machine earns and costs today, and you can adjust for your own expectations.

Daily Revenue and Cost at Three Electricity Rates

The Profitability Verdict

At $0.04/kWh (Quebec hydroelectric): Every single model is profitable. The base S19 earns $0.65/day profit. The S21 XP earns $7.22/day profit. At cheap electricity, even the least efficient machine makes money. The question is not if you profit but how fast you recover your hardware cost.

At $0.12/kWh (US average): The picture changes dramatically. The base S19 is running at a $5.59/day loss. The S19j Pro loses $4.71/day. The S19k Pro loses $3.19/day. The S19 XP loses $3.11/day. Meanwhile, the S21 series is still losing money at this rate: the S21 at -$2.28/day, the S21 Pro at -$0.82/day, and only the S21 XP approaches break-even at +$0.22/day. At average US electricity prices, mining is difficult for any hardware.

At $0.20/kWh (expensive markets): Nothing is profitable. The S21 XP loses $6.78/day. The base S19 loses $11.83/day. At this rate, mining only makes sense as a space heater replacement during winter months — and even then, only with the mental model that you are paying for heat and the bitcoin is a partial rebate.

Repairability: Parts, Cost, and Longevity

This is where D-Central’s experience as Canada’s leading ASIC repair service gives us a perspective that no spec sheet can provide. We have repaired over 2,500 miners since 2016. We have seen what breaks, how often it breaks, and what it costs to fix. The repairability difference between the S19 and S21 is significant and should factor into your purchase decision.

S19 Series: The Repair-Friendly Workhorse

The S19 series has been in the field since 2020. Five-plus years of global deployment means:

• Abundant replacement parts: BM1398 chips, hashboards, control boards, fans, and PSU components are widely available. Both new-old-stock and salvaged parts are on the market. Hashboard prices have dropped significantly as more units get decommissioned from large farms.
• Well-documented failure patterns: The repair community knows exactly what fails on S19 units and why. Temperature sensor issues on S19 Pro hashboards, power delivery failures on S19j Pro units, and fan bearing wear are all well-characterized with established repair procedures.
• Abundant repair documentation: Schematics, diagnostic guides, and repair videos are widely available. The S19 is one of the most-documented miners in ASIC repair history.
• Third-party firmware support: Braiins OS+, VNish, and LuxOS all fully support S19-series hardware, enabling undervolting that reduces thermal stress and extends component lifespan.
• Lower repair costs: A typical hashboard repair on an S19j Pro runs $150-400 CAD depending on the failure. Control board replacements are $100-250 CAD. These are reasonable repair costs relative to the machine’s value.

S21 Series: The New Kid with Growing Pains

The S21 series is still in its early field life. This means:

• Limited replacement parts: BM1370 chips are expensive and harder to source. Hashboards are rarely available outside of Bitmain’s direct warranty channel. Salvage parts barely exist because few S21 units have been decommissioned yet.
• Developing failure patterns: The repair community is still learning what fails on S21 hardware. With 4 hashboards instead of 3, and a denser BM1370 chip layout, there are more components that can fail. The failure modes are being documented in real-time.
• Fewer repair resources: Schematics are less widely available. Repair guides are scarce. Most independent repair shops are still building their S21 expertise.
• Limited firmware options: Stock Bitmain firmware is the primary option for most S21 users. Third-party firmware support is developing but not mature.
• Higher repair costs: When S21 repairs are possible, they tend to be significantly more expensive. BM1370 chip replacements cost more, diagnostic time is longer due to less documentation, and parts sourcing adds lead time. Expect $300-700+ CAD for hashboard-level repairs.

Repair Cost Comparison

The bottom line: the S19 is a mature, repairable machine. When something breaks, fixing it is straightforward and affordable. The S21 is still in its “new car” phase — parts are expensive, expertise is developing, and a major failure can be economically devastating relative to the machine’s value. This gap will narrow over the next 2-3 years as the S21 install base grows and the repair ecosystem catches up.

Resale Value and Depreciation

ASIC miners are depreciating assets. New, more efficient hardware is always coming. Understanding depreciation curves helps you make better purchase timing decisions and evaluate the true cost of ownership.

Historical Depreciation Patterns

The S19 series provides a well-documented depreciation case study:

• S19 Pro at launch (2020): ~$2,500-3,500 USD
• S19 Pro during 2021 bull market: ~$8,000-12,000 USD (yes, above launch price)
• S19 Pro post-2022 crash: ~$1,500-2,500 USD
• S19 Pro in 2024 (post-halving): ~$800-1,500 USD
• S19 Pro today (2026): ~$400-800 USD depending on condition and seller

That is roughly an 80-85% depreciation from launch price over five years. BTC price movements can temporarily inflate used hardware prices (as we saw in 2021), but the long-term trend is relentless downward as newer, more efficient hardware makes older machines less competitive.

The S21 is still early in its depreciation curve. New S21 units sell for a premium today. Within 2-3 years, expect the same pattern: prices will decline as the next generation (S23 or whatever Bitmain names it) arrives. This is the nature of technology assets in a rapidly advancing field.

Resale Strategy Implications

Here is a contrarian take: buying a used S19j Pro today at $500-700 USD might be a better investment than buying an S21 at $3,000+ USD — if your electricity is cheap. The S19j Pro at $0.04/kWh earns back its purchase price in a few months. The S21 at $0.04/kWh takes considerably longer to reach payback, and during that time it is depreciating. The S19 has already taken its depreciation hit. You are buying near the floor.

The counterargument: the S21 will remain competitive for years longer. It will survive difficulty increases that push the S19 below profitability. If BTC price rises substantially, the S21 earns proportionally more. And when you eventually sell the S21, it will retain more residual value than the S19 would have.

Both arguments have merit. The right answer depends on your time horizon and risk preference.

Space Heater Conversion Potential

D-Central pioneered the Bitcoin space heater concept — taking ASIC miners and converting them into dual-purpose heating and mining appliances for Canadian homes. This is where the S19 vs S21 comparison gets interesting, because the two generations serve different roles in a space heater deployment.

The S19 as a Space Heater: The Value Champion

The S19 series — particularly the S19 and S19j Pro — is the ideal space heater candidate for several reasons:

• Low acquisition cost: Used S19j Pro units can be purchased for $500-700 USD. If the machine’s primary job is heating, the low buy-in makes the economics irresistible.
• Excellent heat output: 3,068-3,250W of heat output is equivalent to two standard electric space heaters. Enough to heat a large room, garage, or workshop.
• Proven reliability: Five years of field data means you know exactly what to expect. These machines are workhorses.
• Undervolting flexibility: With Braiins OS+ or VNish, you can dial the power down to 1,500-2,000W for shoulder-season heating when you do not need full blast. This also drops noise to livable levels.
• Repair-friendly: When something breaks (and it will eventually), parts are cheap and available.
• Bitcoin offset: Even at moderate efficiency, the bitcoin mined during heating season meaningfully offsets the electricity cost. In Quebec at $0.04/kWh, an S19j Pro running as a heater during a 6-month heating season costs roughly $530 in electricity and mines roughly $750 worth of bitcoin at current rates. Your heater pays you.

The S21 as a Space Heater: Overkill (For Now)

Using an S21 as a space heater is like using a Ferrari as a pizza delivery car. It works, but you are massively overpaying for the capability you actually need. The heat output is similar to the S19 (because wattage is similar), but you are paying 4-5x more for the hardware. The additional hashrate efficiency of the S21 does earn more bitcoin per watt, but that advantage does not justify the capital premium when the primary use case is heating.

That said, in 3-4 years when the S21 has depreciated to S19-level pricing, it will become the superior space heater candidate — more efficient mining while producing the same heat.

Who Should Buy Which? Decision Matrix

Enough data. Here is the direct advice, broken down by miner profile.

The New Miner (First ASIC Purchase)

Budget under $1,000: Buy a used S19j Pro or S19k Pro. Learn how mining works, get familiar with pool configuration, noise management, and electrical requirements without risking serious capital. If you decide mining is not for you, you are out a few hundred dollars, not thousands.

Budget $1,500-3,000: This is the decision zone. If your electricity is under $0.06/kWh, the S21 is the right machine — you will earn back the premium through superior efficiency over its multi-year lifespan. If your electricity is above $0.10/kWh, buy the cheaper S19-series machine and invest the savings in better electrical infrastructure, noise management, or more machines.

Budget $3,000+: Buy the S21 Pro. It is the sweet spot of the S21 lineup — better efficiency than the base S21, lower price than the S21 XP, and enough hashrate to make a meaningful contribution to your chosen pool.

The Existing S19 Owner (Upgrade Decision)

Electricity under $0.06/kWh: Keep your S19 running AND buy an S21 if you have the circuit capacity. The S19 is still profitable at cheap rates — there is no reason to sell it. Add the S21 as incremental hashrate.

Electricity $0.06-0.12/kWh: Consider selling the S19 and buying an S21. The S19 is barely profitable or unprofitable at these rates, while the S21 has better margins. The sale proceeds from the S19 partially offset the S21 cost.

Electricity above $0.12/kWh: Do not upgrade — exit mining or relocate your operation. Neither the S19 nor S21 is profitable at these rates unless you are using the heat. If you are using the heat, keep the S19 as a space heater and skip the S21 entirely.

The Home Miner / Heater Operator

Primary goal is heating: Buy a used S19j Pro and run it through a D-Central Space Heater enclosure. The bitcoin is a bonus. Do not overspend on hardware when the primary output is heat.

Primary goal is mining + heating bonus: Buy the S21. You get maximum hashrate efficiency, and the heat is a welcome byproduct during winter. Budget for noise management — even in a basement, 75 dB is loud.

The Farm Operator (Multiple Units)

Expanding a facility: S21 series only. When you are buying 10+ units, the efficiency difference compounds dramatically. Ten S21 units produce 2,000 TH/s at 35,500W. To match that hashrate with S19j Pro units, you need approximately 20 machines drawing 61,360W — nearly twice the power infrastructure. The S21’s per-unit premium pays for itself through reduced electrical buildout costs.

Replacing decommissioned units: S21 Pro or S21 XP. When you are cycling out old hardware, always replace with the best efficiency available. The per-terahash cost of electricity is the dominant operating expense at scale.

Quick Decision Summary

Firmware and Software Ecosystem

The firmware running on your miner determines its real-world performance — hashrate, power consumption, noise levels, and fan behavior. This is an area where the S19 series has a decisive advantage today.

S19 Firmware Options

• Bitmain Stock Firmware: Default, no customization. Runs at full power, no undervolting, aggressive fan curves. Works, but suboptimal for home miners.
• Braiins OS+: The gold standard for S19 optimization. Autotuning, undervolting, custom fan curves, and Stratum V2 support. Can reduce power by 20-40% while retaining 70-85% of hashrate. Free for Braiins pool users, paid license for other pools.
• VNish: Popular alternative with excellent S19 support. Aggressive autotuning, per-chip optimization, immersion mode profiles. Licensed per machine.
• LuxOS: Another solid option with S19 support. Good UI, reliable autotuning, managed service model.

S21 Firmware Options

• Bitmain Stock Firmware: Currently the primary option for most S21 operators. Bitmain’s stock firmware on the S21 is more refined than older generations, with better thermal management out of the box.
• Braiins OS+: S21 support is available but still maturing. Not all autotuning features are as refined as on the S19 platform. Improving with each release.
• VNish / LuxOS: S21 support in various stages of development as of early 2026. Check vendor websites for current compatibility.

For home miners who rely on undervolting and custom fan curves to make mining livable, the S19 series currently offers a significantly better firmware ecosystem. This advantage will erode as third-party firmware catches up with S21 support, but as of today, it is a real and meaningful difference. See our Antminer Undervolting Guide for specific instructions on configuring third-party firmware for home use.

Installation and Basic Diagnostics

Both the S19 and S21 follow the same basic installation process. The differences are minor but worth noting. Here is a quick diagnostic check you can run on either generation once the machine is online.

# Connect to your miner via SSH (default password: root)
ssh root@MINER_IP_ADDRESS

# Check miner status and hashrate
cat /tmp/freq
cat /tmp/hashrate

# View kernel log for errors (chip failures, temp warnings)
dmesg | tail -50

# Check fan speeds (RPM)
cat /tmp/fan_speed

# View chip temperatures
cat /tmp/temp

# Check network connectivity
ping -c 3 stratum.braiins.com

# View uptime
uptime

The key difference: S21 units have 4 hashboards while S19 units have 3. When checking diagnostic output, expect 4 board entries instead of 3. A healthy S19 should show 3 boards with temperatures in the 50-75C range. A healthy S21 should show 4 boards in the same temperature range. Any board showing 0 TH/s or temperatures above 90C indicates a problem requiring investigation.

The Bigger Picture: Mining Decentralization

At D-Central, we talk about the decentralization of every layer of Bitcoin mining. This comparison guide would be incomplete without addressing what your hardware choice means for the network.

The S19 series represents the largest installed base of any mining generation in Bitcoin’s history. Millions of these machines are deployed globally. Many are in large institutional farms, but a significant and growing number are in homes, garages, basements, and workshops — run by individuals who care about Bitcoin’s decentralization.

When home miners buy used S19 hardware at depreciated prices and put it to work, they are redistributing hashrate from centralized facilities to decentralized locations. Every S19j Pro running in a Canadian basement is hashrate that is not concentrated in a single facility controlled by a single entity. This matters for Bitcoin’s censorship resistance, geographic distribution, and political resilience.

The S21 series will eventually reach the same stage — affordable enough for home miners to deploy widely. Until then, the S19 serves a crucial role in the decentralization mission. Do not underestimate the value of an “old” machine that puts hashrate in the hands of individuals instead of institutions.

This is what we mean by “Bitcoin Mining Hackers.” Taking institutional-grade hardware and hacking it into accessible solutions for the sovereign individual. Whether that hardware is a $500 used S19j Pro or a $3,000 new S21, the mission is the same: decentralize hashrate, strengthen the network, stack sats. Every hash counts.

Frequently Asked Questions

Why D-Central for Your S19 or S21

D-Central Technologies has been in the Bitcoin mining business since 2016. We are not a faceless online store that ships you a box and disappears. We are a full-service mining operation based in Laval, Quebec, Canada, with a team that lives and breathes Bitcoin mining every day.

Here is what we bring to the S19/S21 decision:

• We sell both generations. New S21 units and used/refurbished S19 units. We will tell you which one is right for your situation — even if the cheaper option is the right answer.
• We repair both generations. Over 2,500+ miners repaired since 2016. Board-level diagnostics, chip replacement, firmware recovery. If your machine breaks, we fix it.
• We host miners. Our facility in Laval, QC runs on cheap Quebec hydroelectric power. If home mining is not viable in your area, we can host your machine at competitive rates.
• We build space heaters. The D-Central Bitcoin Space Heater line was designed and built in Canada for Canadian winters. We pioneered this concept.
• We consult. Not sure what to buy? Our mining consulting service will evaluate your electrical setup, budget, goals, and electricity rate to recommend the right hardware and configuration.
• We are Bitcoin Mining Hackers. We take institutional-grade technology and hack it for the individual. Our mission is the decentralization of every layer of Bitcoin mining. Every hash counts — whether it comes from a veteran S19 or a brand new S21.

Questions? Call us at 1-855-753-9997 or contact us online. We respond to every inquiry.