Learn from a pair of at-home miners who constructed their own hot tub using heat exhaust from bitcoin mining machines.
This article shares the first-hand experience of Erin Malone and Sage S., two at-home miners who used the heat from their machine for recreational purposes while also discovering new blocks for the Bitcoin network. This article was first published on Substack, and it has been revised and expanded for the Braiins blog.
Who says bitcoin mining can’t be fun?
Home miners who want to take their bitcoin operation to the next level can use this article to learn how to engineer a bitcoin mining machine-heated hot tub. We started our hot tub project with two goals in mind.
Our purpose was not necessarily to save money. Miners reading this article may find necessary parts for cheaper prices elsewhere. We simply wanted to make the setup as simple as possible.
First, here’s a bit about us and how we started mining bitcoin.
Sage’s bitcoin mining journey began in 2012. Back then, he started with just a few weeks of GPU mining, and he was hooked. He picked it up again in 2016 after building an even more sophisticated custom GPU mining rig. Now, of course, he mines bitcoin with a hot tub.
Erin met Sage earlier this year (in 2022). At the time, Erin was heating her apartment by mining bitcoin with an Antminer S9. Outside the same apartment, Erin also had a hot tub. After lots of conversations about their experiences mining, Sage and Erin put their “Braiins” together and created the Hot Tub Mining Machine, which this article explains in detail how to replicate for yourself.
Before you start building your hot mining-heated hot tub, here’s an important safety warning.
This project combines liquids and electronics. At best, nothing goes wrong. At worst, you get water on the machine and potentially kill it (or yourself). The potential exists for a shocking wake-up call; electrocution. So, we would advise only using an outlet with a properly tested and functioning GFCI breaker. This how-to is for demonstration purposes only. Mixing water and electricity can be dangerous. Please get an electrician to assist if you are at all unfamiliar with necessary safety aspects of this project.
Here’s a video walk through of our hot tub.
To get started, here are our shopping lists for tools and supplies.
We chose this kit because it's a complete kit. It comes with four (4) cooling plates to sandwich the three (3) ASIC boards, correctly sized thermal transfer pads, sandwich brackets, and long bolts and nuts to hold the whole thing together. Find it on eBay here.
We chose one with a flat bottom to house the miner. Find it on Amazon here.
You will need this to serve as a water reservoir. Find it on Walmart here.
This will work to transfer the heat from the mining machines to the hot tub water. Find it in Amazon here.
This is the hard line tubing that will run from the stainless hot tub coil into the water pump. We bought ours from Home Depot, and you can find it online here.
This pump needs to be able to handle high temperatures, of course, and it will work to circulate the water loop. Find it on Amazon here.
This water will fill the reservoir. A more permanent version of this setup could substitute food-grade propylene glycol and perhaps substitute automotive grade rubber or silicone radiator and fuel hoses, as they are higher temp, offer more insulation, and seal easier around fittings. Find it on Amazon here.
These will be used for the pex tubing. Find them on Amazon here.
This tape will be wrapped around the joints that connect the stainless steel coil. Find it on Amazon here.
This will serve as a remote temperature monitor for the hot tub. Ours was purchased from AC Infinity. Find it online here.
This extender will be helpful for miner connectivity. Find one on Amazon here.
Last but not least, you'll need an actual hot tub. We used an Intex PureSpa 4 person inflatable hot tub. Find it online from Walmart here.
For this project, we used an Antminer S9 running Braiins OS+ firmware.
Start by installing Braiins . Depending on how your S9 is configured, you may need to hop in the Braiins Telegram group to troubleshoot the right way to install. ad issues ith this particular S9, and the Braiins team was extremely helpful and responsive.
Once installed, access the Braiins software by typing in the static IP of your miner. From there, you can throttle your miner’s power consumption up or down, adjust chip temperature targets, enable autotuning, etc.
For this process, the tools required include a Phillips screwdriver and a clean, dry, non-metallic workspace.
For this process, the tools required are pliers.
Congrats, the easy part is done.
For this process, the tools required are pliers and scissors.
For this process, the tools required are a Sharpie marker, a drill, a ¾ drill bit, and a knife.
See the embedded video below for this step.
The embedded video below is part one of video recordings for Part 6.
The embedded video below is part two of video recordings for Part 6.
For this process, the tools required are a single ear hose clamps and a crimper.
For this process, the tools required are scissors and a crimper.
For this step, please ensure the miner is not plugged into any power source. It's good to have a helper on this step, both for safety and to keep the pipes from getting kinky.
We started running the S9 at 1000w as that is what we typically have it set when using it as a space heater in the winter. It is also most efficient at that power setting.
At first, our target temperature for the Hot Tub Mine Machine was 100-102°F, as that is the ideal use temperature. At 1000w, the temperature was rising too quickly so we throttled down to 700w. Every time you change the power consumption, the Braiins autotuning can take up to 6 hours to tune. So you want to let it finish tuning before you jump to any conclusions. At 700w, the temperature rose to 105°F. Too hot. At 500w, the temperature held between 99-100°F. Just right.
500w seemed like a good base (and we could boost the tub a couple degrees if needed with the main hot tub heater), but the outside temperature shifted drastically and the hot tub temperature sank to 92°F. The chip temperature dropped to 54°C. We live in Northern California and it’s pretty common to have 50 degree temperature shifts between day and night in the summer.
We then boosted the power consumption to 600w and let it autotune. The chip temperature rose close to 60°C and the hot tub temperature started going back up. This was close to the previous chip temperature that heated the tub to 99-100°F.
So, we wondered if there was a way to keep the chip temperature at 60°C and have Braiins do dynamic power scaling to throttle the power consumption up and down to keep the chip temperature constant. Unfortunately, the only way to do this currently is to run a script. As neither one of us knew how to code, that was not going to happen.
Note: we did try the dynamic power scaling - setting the chip target to 60°C, but the software jumped around and really couldn’t figure it out. The efficiency was very poor, it never really tuned itself, and it ran the fan continuously at 100%. Since writing this, The Home Assistant Braiins integration has been brought to our attention and we’ll be incorporating that into our build: https://braiins.com/blog/controlling-home-temperature-bitcoin-mining-heat.
Braiins (OS+) does however store your previous autotunes. So we let it tune at 800w, 700W, 600W, and 500W, so we could switch back and forth as needed depending on the ambient temperature and would not have to wait for a 6-hour tune.
We found a chip temperature between 60-69°C to be ideal for maintaining hot tub heat levels of 99-100°F degrees during ambient temperatures of 50-100°F.
We used a power meter to measure the power consumption of the following:
We ran the power meter and found the hot tub heater to use 17.76kwh for 48 hours, set at the base temperature of 96°F at ambient temperature range 50-100°F. This averages out to 370 watts per hour.
Running the hot tub heater costs $2.57 per day at our highest energy tier of $.29/kWh.
The hot tub average temperature with the miner running at 500w is 96°F (ranging 92-100) at ambient temperature range 50-100°F.
At this current moment in time, bitcoin is $23.8k and the hash rate is 192.93 EH/s. At 500w, the miner’s hash rate is 6.15 TH/s (slightly more efficient at 600w and 700w).
Running the miner at 500w costs $3.49 per day at $.29/kWh. Once you calculate the sats earned it comes out to a net cost of $2.00 per day.
We save 57 cents (about 2500 sats) per day using the miner.
Note: during the days of testing, the ambient temperatures were the exact same every day. Overnight and mornings would drop to 50°F and by the afternoon would reach 100°F.
We’re currently in a bear market and the bitcoin price is very low. The breakeven price right now for free heating is when the bitcoin price hits $40k (assuming hash rate doesn’t change).
By running the miner slightly hotter at 600w and 700w, the efficiency is greater and gets us closer to the desired use temperature (100-102°F). Our plan is to keep the base temperature around 96°F when not in use, and turn the power usage up a few hours before use - the same as we would the regular hot tub heater.
Note: We are using a 5-year-old mining machine for this project. Any of the new generation Antminer S19 miners would be break-even or profitable at current prices and hashrate, although not all of these models have compatible versions of the Braiins OS+ firmware currently available.
This article was written for the Braiins blog by Erin Malone and Sage S., both of whom are home miners with a knack for DIY bitcoin projects. Follow them on Twitter for more hot tub mining tips and to ask any questions after reading through this guide.
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