Air, hydro or immersion – which cooling for which site

Most current SHA-256 models come in several cooling variants. The chips are the same, the effort at the site is not.

Air

Two to four fans push air through the heatsinks. The unit needs only power and network.

• Connection: single-phase, 220–277 V at Bitmain.
• Power: around 3.5 kW per unit for current models.
• Noise: 76 dB(A) according to the Antminer S21 manual, continuously.
• Effort: intake air, exhaust air and dust filters. The waste heat comes as warm air and can only be used where air is needed.

Suitable for halls, containers and anywhere noise does not matter and the number of units starts small.

Hydro

Cold plates on the hashboards pass the heat to a closed water circuit. There are no fans in the unit.

• Connection: three-phase, 380–415 V.
• Power: 4 to 11 kW per unit, depending on the model.
• Noise: in the unit only the pump; the rest depends on the dry cooler, if you need one.
• Effort: pump, piping, coolant and either a dry cooler or a heat consumer such as a buffer tank.

Suitable if you want to use the heat, if it has to be quiet or if a lot of power has to fit into little space.

Immersion

The unit sits without fans in a tank of electrically non-conductive liquid. The liquid absorbs the heat and releases it through a heat exchanger.

• Connection: single-phase or three-phase depending on the model; the voltage is stated on the product.
• Noise: very low.
• Effort: tank, liquid, circulation and heat rejection. Any work on the unit means lifting it out of the liquid.

Suitable for installations designed for density, dusty environments or overclocking, with an operator who maintains the tank.

Matching by site

• Hall or container without heat demand: air. Lowest entry costs.
• Residential building, hotel, business with heat demand: hydro. The heat arrives in a form that a heating system can use.
• Hot or dusty climate: hydro or immersion, because the electronics never see outside air.
• Few units, no specialist staff: air. Hydro and immersion require a circuit that someone plans and monitors.

What you need to clarify before ordering

1. What voltage and how many phases are available at the site?
2. Where does the heat go in summer?
3. Who maintains the circuit or the tank?

If one of the three questions cannot be answered for hydro or immersion, air is the right choice. You can find the units of all three designs in the shop.

Sources

• Bitmain: Antminer S21, specifications
• Bitmain, manuals (PDF): S21, noise level, S23 Hyd, connection and coolant

As of October 2026.