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Progress report · Sep 12, 2026 · 5 min read

The S21+ Hyd is the best-returning machine on our floor

395 TH/s from one box at a settled entry price, and one of the strongest first-year returns we host. Seventeen months in, here is what it has banked and what is left in it.

An Antminer S21+ Hyd photographed beside a dry-cooler array

Bitmain Antminer S21+ Hyd (395 TH/s)

Seventeen months in

A 395 TH/s S21+ Hyd at 15 J/TH, bought at $5,848 and landed at $7,240, and racked at our UAE site at 6¢ in April 2025 — the site we build around water: dedicated hydro plant, better than 99% uptime, and in-warranty repairs handled by a manufacturer centre nearby. It has mined and kept 0.1054 BTC in 570 days — worth about $8,151 today — for $5,242 of electricity, about $49,700 a coin.

$2,909 of cashflow, about 40% of its landed cost, on a machine well under half way through its expected life. All 570 of those days have been in the UAE, and at 15 J/TH it is nowhere near needing cheaper power: hosting it at 6¢ still leaves a wide margin.

Chart: Banked so far, and where the forward figures put it by the 2028 halving.

Why the hydro version returns more

This machine returns about 28% in its first year at our UAE site — among the highest figures of anything we currently host.

The reason is density. Freight, import duty, customs, rack space and setup cost roughly the same for a 225 TH/s box as for a 395 TH/s one, so a hydro machine spreads them across nearly twice the output. At 15 J/TH the efficiency is already good; the per-terahash overhead is what turns good into best.

That only works if your site can take hydro. Ours can — all three of our sites run water loops — which is why we stock these rather than treating them as a specialist item.

395 TH/s in one box spreads every fixed cost over nearly twice the hashrate of an air-cooled machine.

A row of V-frame dry coolers on a concrete pad
The dry coolers size the site, not the machines. Add hydro capacity and this is the part that has to grow first.

What is left in it

At today’s difficulty and with bitcoin back at its previous high, it has another 0.089 BTC and roughly $11,070 between now and April 2028 — the largest forward figure of anything in this generation we host. That lands it around 1.9× its full landed cost by the halving, with a long life after it.

At 15 J/TH it will still be clearing at 6¢ after the next halving and has years beyond that at Nigeria’s 3.9¢. Seventeen months in, the machine is barely a third of the way through what it is going to do.

The machines that make cheaper bitcoin than this does.

Which machines this covers

The other side of this machine

Antminer S21+ Hyd review: 395 TH/s in one box, at the best entry price it has had — Bitmain's 15 J/TH water-cooled machine packs the most hashrate per box of any we list at its efficiency. It makes a coin dearer than the 13 J/TH machines above it, so its case is the entry price and a site with cheap power.

Disclosure

Firsthand Bitcoin sells and hosts mining hardware, including this machine. No manufacturer, distributor or affiliate programme paid for or reviewed this page and we take no commission on the links above. Historical figures are computed from daily bitcoin price and network hashprice, each day valued at its own prices. Nothing here is investment advice.