Temperature and efficiency – why cool chips need less power

The efficiency in the datasheet applies to a specific temperature. If the unit runs warmer, it needs more power for the same computing power.

The measurement

Braiins measured this in 2021 on the Antminer S19j Pro, at fixed frequency (550 MHz) and fixed voltage (13.5 V), with power consumption taken at the wall. The temperatures were measured at the hashboard, not in the room:

• at 20 °C: 2.5 kW, which corresponds to 24 J/TH
• at 75 °C: 3.55 kW, which corresponds to 34 J/TH

The hashrate was the same in both cases; Braiins calculates the J/TH values with the stock 104 TH/s. The difference of a good 40% is caused by temperature alone.

Why this is so

Braiins does not name the cause. The usual explanation from semiconductor engineering: a chip loses current even where it is not switching at that moment. These leakage currents rise sharply with temperature. They contribute nothing to the hashrate and turn entirely into heat, which in turn has to be removed.

Braiins finds the effect more pronounced in the S19 generation than in the S9 and the S17 generation. For the S21 series and current Whatsminers we know of no comparable published measurement; the principle is the same.

What the datasheet says

• Antminer S21: Bitmain states 17.5 J/TH at 25 °C ambient temperature. The unit may be operated up to 45 °C, but it does not reach the datasheet efficiency there.
• Whatsminer M60S: MicroBT states 18.5 J/TH at 25 °C with a tolerance of ±5% and an operating range of −5 to 35 °C.

So the permitted maximum temperature only tells you up to what point the unit runs. It tells you nothing about what it consumes there.

What that means in money

A unit that continuously draws 3.8 kW instead of 3.5 kW consumes around 2,600 kWh more per year without delivering a single additional hash. With a tight margin, that is the difference between profit and loss.

How to lower the temperature

1. Keep the intake air cool. Warm exhaust air must not get back to the intake side. Separate the cold and hot sides structurally.
2. Let the fans spin faster. The extra consumption of the fans is small compared with the saving at the chips. It does get louder, though.
3. Keep the heatsinks clean. Dust acts like a layer of insulation.
4. Autotune when the unit is cool. That is why Braiins OS sets the fans to full speed during calibration.
5. With hydro, keep the inlet temperature low, as far as your heat consumer allows.

The trade-off in heat reuse

Anyone heating with the miner wants warm water. Warm water means warm chips and therefore more power per terahash. For the heat balance this is not a loss, because the additional power arrives as heat in the heating circuit. For the mining revenue it is one. So choose a flow temperature as low as your heating system permits.

Sources

• Braiins: impact of temperature on the efficiency of the Antminer S19, 2021
• Rosselló et al.: A Fast Concurrent Power-Thermal Model for Sub-100nm Digital ICs, on the temperature dependence of leakage power
• Bitmain: Antminer S21, specifications
• MicroBT: Whatsminer M60S, manual (PDF)

As of October 2026.