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Crypto Miners Direct

Hardware guide

Hydro Mining Explained

Understand how hydro-cooled miners and their coolant loop work, which parameters the manufacturer sets, and how to size flow from heat load.

Published October 1, 2026 · Reviewed by James Emerson

Hydro mining means cooling ASIC miners with a closed loop of water-based coolant instead of fans. Each machine has cold plates against its chips; pumps push coolant through them, and the heat is carried to a heat exchanger and rejected outdoors by a dry cooler or cooling tower. The machine is only half of the system. The loop has to deliver the flow, temperature, pressure and coolant quality the manufacturer specifies, continuously, to every unit.

Key points

  • Heat load equals electrical load. Size the loop for the full wall power of every machine on it.
  • Required flow follows from Q = ṁ × c × ΔT. For water, 10 L/min carries about 7 kW at a 10 °C rise.
  • Manufacturers publish limits for inlet temperature, flow, pressure and coolant chemistry. Operating outside them can damage cold plates and is commonly excluded from warranty.
  • Clean and flush the pipework, bleed the air and leak-test with circulation before any miner is powered.
  • Electrical supply for hydro units is typically three-phase and must be designed and installed by a qualified electrician to local code.

Inside a hydro-cooled miner

A hydro-cooled miner replaces finned heatsinks with cold plates: flat metal plates with internal channels, pressed against the chips. Coolant enters through one quick connector, runs through the plates, and leaves through another. There are no chassis fans, the electronics are closed off from dust, and the machine itself is quiet.

Because liquid removes heat from a much smaller surface than air can, manufacturers put more chips and more power into one hydro chassis. Bitmain publishes 5,676 W for the Antminer S21 XP Hyd., and MicroBT publishes 7,344 W for the WhatsMiner M63S 408T.

The loop, component by component

  1. Quick connectors and hoses join each miner to the supply and return manifolds. They self-seal when unplugged so a single unit can be removed.
  2. Manifolds in the rack or cabinet distribute supply coolant to every machine and collect the return. They need to be balanced so each unit gets its share.
  3. Circulating pumps provide flow against the pressure drop of the miners, hoses, filters and heat exchanger. MicroBT recommends stainless steel pumps with one running and one on standby.
  4. Filters. MicroBT specifies a main-line filter finer than 100 mesh and recommends a 10-micron side-stream filter.
  5. Expansion tank, relief valve, air vents and drains. The tank absorbs the volume change as coolant warms. MicroBT requires a 4 bar relief valve and a constant-pressure expansion tank, automatic vents at high points and drains at low points.
  6. Plate heat exchanger. Thin corrugated plates separate two liquids so that heat passes but the fluids do not mix.
  7. Dry cooler or cooling tower. A dry cooler is a finned coil with fans, like a large radiator; it uses no water but cannot cool below ambient air temperature. A cooling tower evaporates water to reach lower temperatures at the cost of water consumption and treatment.
  8. Controls. Sensors for supply and return temperature, flow, pressure and leaks, with pump and fan speed control. The pump, tank, filters and controls are often packaged as a CDU (cooling distribution unit).

One loop or two

In a single-loop system the same coolant runs through the miners and the dry cooler. It has fewer parts, but all the outdoor pipework and the cooler are filled with miner-grade coolant, and everything in contact with it must meet the manufacturer's material rules.

In a two-loop system a plate heat exchanger separates the clean loop through the miners from the loop that goes outdoors. Vendors name these differently (primary and secondary, or internal and external circulation; MicroBT calls the arrangements single cycle and double cycle). The miner-side loop stays small, clean and tightly controlled, while the outdoor loop can use a cooling tower or feed a heating system. The cost is an extra pump set and a few degrees of temperature difference across the exchanger.

The parameters the manufacturer sets

These are manufacturer-published values for two current hydro machines. Your model's own specification is the authority.

Parameter Antminer S21 XP Hyd. (Bitmain) WhatsMiner M63S 408T (MicroBT)
Hashrate 473 TH/s 408 TH/s
Power at the wall 5,676 W at 35 °C inlet 7,344 W
Inlet coolant temperature 20–50 °C 25–55 °C in normal mode
Flow per machine 8–10 L/min at least 10 L/min
Maximum pressure 3.5 bar 400 kPa (4 bar)
Coolant Antifreeze, pure water or deionized water Pure or distilled water plus corrosion inhibitor, plus antifreeze as needed
AC input 380–415 V three-phase 380–480 V

What each parameter protects:

  • Inlet temperature. Too hot and the chips overheat; too cold and the machine will not run. Bitmain states the S21 XP Hyd. cannot start below 20 °C inlet. MicroBT recommends a bypass valve on the cooler side so that supply temperature does not fall below the minimum in cold weather, and asks for control within ±2 °C.
  • Flow. Low flow means a larger temperature rise across the machine and hot outlet-side chips.
  • Pressure. MicroBT warns that above 400 kPa the cold plates deform and may leak.
  • Coolant chemistry. Bitmain's shop listing gives pH ranges by coolant type (antifreeze 7.0–9.0, pure water 6.5–7.5, deionized water 8.5–9.5) and its specification requires replacing the fluid if conductivity reaches 100 μS/cm. MicroBT sets pH 7.0–8.7, makes a corrosion inhibitor mandatory, and prohibits copper in the loop because its cold plates are aluminium and the two metals corrode galvanically.

Sizing the loop

Step 1, heat load. Add up the wall power of every machine. Treat all of it as heat in the coolant.

Step 2, flow. Use Q = ṁ × c × ΔT, where Q is heat in kW, ṁ is mass flow in kg/s, c is specific heat (about 4.18 kJ/kg·K for water) and ΔT is the temperature rise in kelvin. One litre of water is about 1 kg.

For one S21 XP Hyd. at Bitmain's published 5,676 W and a target rise of 10 K:

ṁ = 5.676 ÷ (4.18 × 10) = 0.1358 kg/s = 8.1 L/min

That sits inside Bitmain's 8–10 L/min range. Working the other way, the published range gives:

Per machine 176 machines
Heat load 5.676 kW 999 kW (3.41 million BTU/h)
Flow at 8 L/min each 8 L/min 1,408 L/min = 84.5 m³/h
Temperature rise at that flow 10.2 K 10.2 K
Flow at 10 L/min each 10 L/min 1,760 L/min = 105.6 m³/h
Temperature rise at that flow 8.1 K 8.1 K

The same formula reproduces MicroBT's own guidance: 10 L/min of water carrying 7,344 W rises by 7.344 ÷ (0.1667 × 4.18) = 10.5 K, and MicroBT's operation guide says 10 L/min corresponds to a difference close to 10 °C in normal mode.

Step 3, antifreeze correction. Glycol mixtures carry less heat per litre than water and are more viscous. MicroBT raises its minimum flow from 10 L/min for water to 10.7, 11, 11.4 and 11.6 L/min for 20%, 30%, 40% and 50% glycol. Its table lists the freezing point of 30% ethylene glycol as −15 °C and of 50% as −37 °C.

Step 4, pump duty. The pump must deliver total flow against the loop's pressure drop while keeping miner inlet pressure under the limit. MicroBT's table gives 63.6 kPa across one miner at 10 L/min with water and 88.1 kPa with 50% ethylene glycol. Add manifolds, filters, valves and the heat exchanger.

Step 5, heat rejection. A dry cooler needs the coolant to be warmer than the outdoor air. Bitmain's S21 XP Hyd. specification says that with its external dry cooler, water leaving the cooler at 35 °C corresponds to a maximum ambient of 30 °C, 45 °C to 40 °C and 50 °C to 45 °C. Rated performance is stated at 35 °C inlet, so check the manufacturer's performance curve before designing for a hotter supply.

Racks or containers

Racks and cabinets go inside a building. MicroBT's hydro units are 2U machines for a standard 19-inch hydro cabinet. Bitmain lists both chassis-style units and wide rack units such as the U3S23H, for which it publishes 1,160 TH/s, 11,020 W and 16–20 L/min in a 900 × 482.6 × 130 mm case. You design the room and plant yourself, which suits permanent sites and heat-reuse projects.

Containers arrive with racks, manifolds, pumps, controls and power distribution pre-installed, and usually pair with a dry cooler or tower mounted on top or alongside. They trade design freedom for speed. See mining containers and containerized solutions.

Common failure modes

  • Leaks. Usually at quick connectors that are not fully seated, or at hose clamps. MicroBT instructs operators to circulate coolant and check for leaks before powering a newly installed miner.
  • Fouling and blockage. Welding slag, rust and debris lodge in the narrow cold-plate channels. MicroBT requires the pipework to be flushed with deionized water and filtered before miners are connected.
  • Air in the loop. Trapped air starves cold plates and can damage pumps. Vent at high points during filling and after any maintenance.
  • Corrosion from the wrong coolant or materials. Tap water, missing inhibitor, or copper, cast iron and carbon steel in the loop attack the plates. Test pH and conductivity on a schedule; MicroBT sets pH checks every two months and recommends replacing coolant after a year.
  • Freezing. Bitmain forbids pure water or tap water where freezing is a risk and reports cold plates burst by ice in units that were moved without being drained. Drain and blow out any machine before storage or transport, and plug the ports.
  • Over-pressure. A closed valve or failed expansion tank can push inlet pressure past the limit as coolant warms.

Both manufacturers state that damage from these causes may not be covered by warranty. Read the terms for your model.

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