Immersion Cooling for Bitcoin Mining: Benefits and Costs

Immersion cooling for mining means the miner doesn't run in air but sits fully submerged in a liquid that doesn't conduct electricity. The fans go, the device becomes almost silent, stays evenly cool and can be overclocked. The heat comes out as fluid at 50 to 60 degrees Celsius that you can heat with. In return you buy a tank, pump, heat exchanger and fluid, and the miner gets no cheaper to run: a kWh of electricity is still a kWh.

Why miners need cooling at all

An ASIC miner turns almost all the electricity it draws into heat. A current device with 200 TH/s at 17.5 J/TH needs around 3.5 kW, as much as two large fan heaters. That heat is produced on a few boards carrying dozens of chips. If the chips get too hot, the device throttles or shuts down.

With air cooling, two to four fans at high speed push air through the case. That works but has three drawbacks: it is loud, it pulls in dust and moisture, and the heat comes out as a large stream of lukewarm air that is of little use. What an ASIC is and which devices exist is explained in Buying an ASIC miner. Why a device at home on household electricity hardly makes a profit is worked through in Bitcoin mining at home.

Liquid absorbs heat far better than air. The two alternatives rest on that: water cooling through cold plates (the manufacturers' "hydro" models) and immersion, where the whole device is submerged.

Single-phase immersion cooling: the standard

In single-phase cooling the miner lies in a tank of dielectric oil with its fans removed. A pump drives the oil through the tank; it picks up heat at the heat sinks and flows to a heat exchanger. There it gives the heat to air (a dry cooler, similar to a car radiator) or to water and returns cooled.

"Single-phase" means the oil stays liquid the whole time. Typical inlet temperatures are around 35 to 45 °C and outlet temperatures around 50 to 60 °C, depending on how hard the device runs and how fast it is pumped.

Almost all mining farms that use immersion work this way. The technology is simple: tank, pump, heat exchanger, temperature sensors. It comes ready-made as containers for dozens of devices and as small tanks for one or two miners.

Two-phase immersion cooling: boiling at the chip

In two-phase cooling the liquid boils directly on the hot components. The fluids are fluorocarbons with a boiling point of around 50 to 60 °C. The vapour rises, condenses on a cooled coil in the lid and drips back. Evaporation absorbs a great deal of heat while the temperature stays almost exactly at the boiling point.

Physically this is the better cooling. In mining it is still rare, for three reasons:

• The fluid is expensive, costing many times as much as mineral or synthetic oil. Whatever evaporates or escapes through leaks has to be topped up.
• The tank has to be sealed. Every time you open it to swap a device, you lose vapour.
• The substances are PFAS, the "forever chemicals". The largest manufacturer, 3M, announced it would stop making PFAS by the end of 2025, and in 2023 five European countries asked the European Chemicals Agency ECHA for a broad PFAS restriction. Planning two-phase today is a bet that you can still buy the fluid in five years.

Dielectric fluids: what goes into the tank

"Dielectric" means the fluid doesn't conduct electricity, so a running miner can sit in it without a short circuit. Water is out of the question; even slight conductivity would destroy the boards.

For mining, single-phase synthetic oil has won out. It is cleaner and more consistent than cheap mineral oil, ages more slowly and is gentler on seals and plastics. A few points that matter in practice:

• Compatibility: Not every oil gets along with every plastic, cable jacket or thermal pad. Fluid manufacturers publish lists of what has been tested.
• Thermal paste: Some pastes slowly dissolve in oil. Devices built for immersion take this into account; converted air-cooled units don't always.
• Cleanliness: Oil doesn't draw in moisture the way air does, but wear particles and dissolved residues collect. A filter belongs in the loop.

Overclocking in oil: more hashrate, worse efficiency

The most cited argument for immersion is overclocking. Because the chips stay evenly cool, you can raise clock speed and voltage. With adapted firmware, 20 to 30 % more hashrate is common.

The catch: a higher clock needs higher voltage, and power use rises faster than hashrate. Efficiency in J/TH gets worse, so the additional hashrate costs more power per TH than the base output. Whether it pays depends entirely on the electricity price.

It works the other way too: in oil you can underclock a device and run it quieter, more efficiently and for longer. For home miners who mainly want heat, that is often the more sensible setting. How the network's hashrate and the difficulty push down your earnings per TH year after year applies in oil just as in air: a miner bought today mines about 36’500 sats per TH/s over six years, two thirds of them in the first two (our home mining research, with the network of our hashrate model).

What an immersion setup costs

Costs split into a one-off purchase and running costs. Prices for small setups vary widely, so the following calculation deliberately uses assumptions.

What earns the cost back is something else: less noise, no dust, a longer device life (immersion vendors promise it; solid long-term data for small setups is scarce) and, above all, usable heat.

Reusing the waste heat: the real advantage

In air, a miner's heat leaves as exhaust at around 40 °C, spread over a large volume. In winter it can heat a room, but hardly warm water or support the house's heating system.

In oil it is different. The heat sits concentrated in a fluid at 50 to 60 °C. A plate heat exchanger can pass it to a water circuit. What you can do with it depends on the temperature your system needs:

For a home miner this means: with immersion and a heat exchanger, the miner can take over part of a house's heating instead of only warming a basement room. Whether that is cheaper than your current heating is shown in the "cost per kWh of heat" table in Bitcoin mining at home: the miner beats electric heating and loses to a heat pump or gas, whose heat costs about a third as much. In place of an electric heater, the electricity is paid for the heat, so the bitcoin only have to earn back the hardware: in our research paper a heater miner does that within one to seven years. An immersion setup adds its €3’800 to what has to be earned back.

On a large scale, liquid-cooled mining heat is already in use. In 2024 MARA started a pilot of around 2 MW in the Finnish region of Satakunta whose heat feeds the district heating network of a town of around 11’000 residents. Heat pumps there raise the warm water to around 80 °C before it flows to homes. That also shows the limit: the miner's temperature alone isn't enough for a district heating network. More on the company is in Marathon Digital.

Noise, space and safety at home

Noise: An air-cooled miner reaches around 75 dB according to manufacturers. In oil the fans are gone; what remains is the pump and, if present, the fan of the dry cooler. You can put that outside and let it spin slowly.

Weight: 150 litres of oil weigh over 120 kg, plus tank and device. A wooden attic floor is not a good place.

Leaks: A leaking pipe spreads oil that is hard to remove. A drip tray under the setup is a must.

Fire safety: Mineral and synthetic oils only burn at high temperatures, but they do burn. A dedicated, fused circuit, a residual-current device and a sensor that shuts down on overheating belong in the setup. If you rent, ask your landlord first, also because of the continuous load.

Maintenance: Swapping a device is an oily business. You lift it out, let it drip and clean it before selling or returning it. Used immersion devices often fetch lower prices than clean air-cooled ones.

Who immersion cooling is worth it for

For farms with cheap power: Here immersion brings measurable gains. More devices per square metre, stable temperatures in hot climates, overclocking in hours of cheap power and underclocking when it is expensive.

For home miners who really want heat: If you already heat electrically or have a buffer tank, a miner in oil can take over part of that work and stay quiet doing it. The extra cost of cooling has to pay for itself over the years from the heating energy saved.

For anyone who wants to make money from mining: probably not. Immersion doesn't lower your electricity price, and the electricity price decides. At around 37 cents in Germany, every kWh in a miner remains a losing deal, in air or in oil. If you want to accumulate bitcoin, a savings plan usually gets you your satoshi more cheaply.