Overclocking and underclocking ASICs: firmware, risks and warranty

Overclocking an ASIC miner usually adds 15–20% hashrate, but power consumption rises faster than hashrate, the machine runs hotter and you will generally lose the manufacturer's warranty. That is why the opposite more often pays off today – underclocking, which lowers consumption per 1 TH/s and extends the time the machine stays profitable. Both are done mainly with alternative firmware: Braiins OS, VNish or LuxOS.

Summary

• Overclocking raises chip frequency and voltage. Hashrate goes up, but efficiency (J/TH) gets worse.
• Underclocking does the opposite: fewer watts, better J/TH, lower temperatures and less noise.
• Alternative firmware takes a fee of 2–2.8% of hashrate, and installing it usually voids the manufacturer's warranty.
• The most common consequences of aggressive overclocking are overheating, restarts, an overloaded power supply and a shorter hash board lifespan.
• Overclocking only makes sense with headroom in cooling and power, typically with water or immersion cooling.

Overclocking vs underclocking: what is the difference

A chip's hashrate rises roughly with frequency, but consumption also rises with the voltage needed for higher frequency. That is why overclocking adds watts faster than terahashes, and the machine uses more energy for every TH/s. Underclocking is the opposite: hashrate drops less than what you save on electricity.

What this means financially is shown by the electricity price up to which the machine pays off. It is calculated as earnings per 1 TH/s ÷ (J/TH × 0.024). At today's 0,84 Kč per 1 TH/s a day:

The efficiency values come from a public firmware comparison (see Sources); earnings apply at today's difficulty and exchange rate, as of 18 Oct 2026. You can see that well-tuned firmware can improve hashrate and efficiency at the same time – because it tunes each chip individually. Crude “full-throttle” overclocking does not.

Which firmware is used to tune ASICs

All three are closed-source software. Only download them from the developer's website – “fee-free versions” circulate on look-alike domains, with hidden fees or hashrate redirected elsewhere. You will find an overview of machine management programs in our article ASIC management software.

How to proceed step by step

1. Find out the exact model and control board type. The S21 series has Amlogic, CVitek and Xilinx boards, and each needs a different firmware image.
2. Note down the pool settings, worker and the machine's IP address.
3. Download the firmware from the developer's official website and check that it supports your model.
4. Install it according to the developer's instructions. On newer Antminers (roughly from March 2024, according to the developers' documentation) the stock firmware blocks third-party software and a remote installation via the developer's tool is required.
5. Set the target: power in W for Braiins OS, a profile for VNish and LuxOS. Start conservatively.
6. Let the machine tune itself (1–9 hours for Braiins OS) and monitor chip and hash board temperatures.
7. After 24 hours, check the average hashrate on the pool, the share of rejected shares and the number of restarts. If something is off, step back.

What can go wrong

Overheating

Stock cooling is designed for stock performance. After overclocking, the fans run at maximum, the machine is louder and the chips may still overheat. Hash board temperature is the best indicator of how close you are to the limit – we explain this in our article on ASIC temperature sensors.

Power supply at its limit

The power supply (APW) is rated for the nominal power draw with a certain margin. Heavy overclocking uses up that margin, and the supply starts overheating or shutting down. A stronger power supply is a further investment that needs to be factored into the payback.

Instability

Overly aggressive settings show up as restarts, hash board dropouts or a higher share of rejected shares. The machine then actually mines less than at stock settings.

Shorter lifespan

Higher voltage and temperature stress the chips, solder joints and fans. A machine that should have lasted several years may start failing sooner – and an overclocked used unit is then harder to sell.

What overclocking does to the warranty

Installing alternative firmware on Bitmain and MicroBT machines usually voids the warranty. All three firmwares can restore the stock software (Braiins via its Toolbox tool, VNish and LuxOS directly from the web interface), but don't rely on being able to claim the warranty. If the machine is under warranty, it is better to tune only within the range offered by the stock firmware.

If hash board errors or overheating appear after tuning, or the machine won't start, our ASIC miner service centre in Prague can deal with it.

When tuning pays off

• Expensive electricity: underclocking raises the break-even point and the machine stays profitable for longer.
• Water or immersion cooling: the cooling has headroom, so mild overclocking won't overheat the chips. We describe the differences between cooling types in our article where air cooling reaches its limits.
• Limited power: if you only have a certain number of kW on site, firmware with a target power setting gets the most out of it.
• It does not pay off for a machine under warranty, in an air-cooled room without headroom, or for an old unit with a weak power supply. There, it is cheaper to buy a more efficient machine.

What next

• ASIC miner service – diagnostics and repairs in Prague if the machine doesn't work as it should after tuning.
• ASIC miner profitability – what machines earn today at stock settings, so you have something to compare against.

Sources

• Braiins OS – supported machines, fee and tuning
• VNish – official firmware website
• D-Central: Antminer S21 firmware by control board
• Spark: comparison of Braiins OS+, VNish and LuxOS