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比特币挖矿内参

How to Build a Hot Tub Mining Machine

Learn from a pair of at-home miners who constructed their own hot tub using heat exhaust from bitcoin mining machines.

Published on Aug 07, 2022
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Published on Aug 07, 2022

Table of Contents

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. 

  • First, we wanted to test if heating a hot tub with a bitcoin ASIC miner instead of the built-in hot tub heater could be done at cost parity. 
  • Second, we wanted to contribute to the global hashrate and security of the Bitcoin network. 

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. 

Before The Hot Tub

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. 

Hot Tub Mining Basics

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. 

Building Your Bitcoin Hot Tub

Part 1: Shopping Lists

To get started, here are our shopping lists for tools and supplies. 

Tools: 

  • Power drill
  • Assortment of drill bits
  • Pliers
  • Scissors
  • Screwdriver set
  • Double sided sticky tape

Parts:

  • S9 Water Cooling Kit

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.

  • Plastic Storage Tub

We chose one with a flat bottom to house the miner. Find it on Amazon here.

  • Plastic Storage Bin

You will need this to serve as a water reservoir. Find it on Walmart here.

  • Fifty (50) Foot Coil of Stainless Steel Tubing

This will work to transfer the heat from the mining machines to the hot tub water. Find it in Amazon here.

  • Twenty Five (25) Feet of Poly Tubing

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.

  • High Temp Water Pump

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.

  • Three (3) Gallons (or More) of Distilled Water

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.

  • Stainless Steel Clips

These will be used for the pex tubing. Find them on Amazon here.

  • Teflon Tape

This tape will be wrapped around the joints that connect the stainless steel coil. Find it on Amazon here.

  • Smart Thermo-Hygrometer

This will serve as a remote temperature monitor for the hot tub. Ours was purchased from AC Infinity. Find it online here. 

  • Network Extender with an Ethernet Port

This extender will be helpful for miner connectivity. Find one on Amazon here.

  • Hot Tub

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.

Our hot tub mining setup

Part 2: Prepping the Mining Hardware

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. 

Braiins OS+矿机自动调整固件
Braiins OS+矿机自动调整固件

Part 3: Building the Hot Tub System

Step 1: Disassemble the Miner

For this process, the tools required include a Phillips screwdriver and a clean, dry, non-metallic workspace.

  1. Unplug power and ethernet cords from miner.
  2. Remove screws from fans and control board cover, unplug all power cables, both fans and 3 asic board cables. Then slide board out of housing and set aside.
  3. Slide three (3) ASIC boards out and gently blow them off with compressed air, there are many s9 cleaning guides available. 

Step 2: The Sandwich

For this process, the tools required are pliers.

  1. Place all the cooling plates down, measure 1 inch from the nipple and mark with a sharpie. Then install the thermal transfer pads on top of all of the cooling plates, leaving the protective film on the top side of the pads. 
  2. Remove the protective film on the first cooling plate, and carefully place the ASIC board on top, with the power connections opposite the nipples on the cooling plate. Continue stacking all the others on top until you have a full sandwich, 4 cooling plates with the ASIC boards between.
  3. Take the 2 metal plates and long bolts, place through one plate and place down on work surface, then place the ASIC sandwich on top of the other metal plate, and tighten it all together snugly (more than finger tight, but don’t crank on it like you’re trying to kill it.)
  4. Use the 3m double sided sticky tape and attach the control board to the top of the sandwich and plug in the three (3) ASIC data cables.

Congrats, the easy part is done. 

Step 2: The Sandwich
Step 2: The Sandwich
Step 2: The Sandwich

Step 3: Tube Assembly

For this process, the tools required are pliers and scissors.

  1. Relocate the large nipple on the manifold from the bottom to the side. These simply unscrew and have o-rings. They do not require being overly tightened. 
  2. Cut 8 sections of tubing around 5” long.
Step 3: Tube Assembly

Step 4: Creating Miner Housing

For this process, the tools required are a Sharpie marker, a drill, a ¾ drill bit, and a knife.

  1. Set the tub upside down, and place the miner down on top of it. Using a sharpie, mark circles around each nipple for drilling, then remove miner and drill the holes
  2. Place circular metal fan cover against plastic tub and mark the circle with sharpie, then carefully cut out with a box knife. Using fan as template, mark and drill screw holes and install fans. 
  3. Cut small 3x3 inch flap into side of plastic tub to feed electrical lines through. 

Step 4: Creating Miner Housing

Step 5: Testing Nipple Holes

See the embedded video below for this step.

Step 6: Stick It!

  1. Place spacers on ground and place tub down, place double side sticky tape on bottom of each cold plate between the nipples, and install the miner into plastic tub as shown with sticky tape.
  2. For extra security to hold the miner down, use some large zip ties and cut holes through the bottom of the tub to secure the miner.

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.

Step 7: You’re Putting Those Where?

  1. Now, flip over the plastic tub again and get all the plumbing fittings ready. There are two things of primary importance here: no leaks and no kinks. Take the blue manifolds and lay them out next to the miner. 
  2. Install all the hoses on the nipples.

Step 8: Crimp the Clamps

For this process, the tools required are a single ear hose clamps and a crimper.

  1. Line up the clamp on the hose, right after the bump in the nipple, and carefully crimp the clamp.

Step 9: Freak-A-Leak

  1. Repeat crimping eight (8) times. 

Step 10: Kriss-Kross

  1. Connect tubing to the manifolds and install the hose clamps.
Step 10: Kriss-Kross

Step 11: The Hook-Up

For this process, the tools required are scissors and a crimper. 

  1. Measure the length you want for the hard line from the miner housing to the hot tub, and cut the line to feed the stainless steel coil that will live in the hot tub. 
  2. Crimp the hot tub lines to the stainless coil.
  3. Measure a shorter piece of the soft silicone tubing to go from the reservoir where the pump will live. 
  4. Place the miner tub on its side, and connect the lines from the hot tub and reservoir, crimp them on both sides.

Step 12: Pump It, Pump It Real Good

  1. Fill the reservoir with several gallons of water.
  2. Install pump and connect the line that feeds to the miner, to the top of the pump (the pressure side).
  3. Plug in 12v pump line so it turns on and look for leaks.

Step 13: Under Pressure

  1. Look for more leaks.
  2. Place a finger over the end of the return line into the reservoir so it pressurizes the loop a little bit to ensure there are no hidden leaks.

Step 14: Burp the Baby

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. 

  1. Now that there are no leaks, this step involves flipping the miner upside down to get any air pockets out of the cooling plates.
  2. Carefully flip the miner upside down, and you will see a rush of air bubbles.
  3. Repeat this step until you see no air bubbles in the system. This will ensure that when the S9 tunes itself, all the chips will be nice and cold with no hot spots in the cooling plate.

Step 15: Start Mining Magic Internet Money

  1. Perform the setup procedure for the wireless adapter and plug it into the miner with an ethernet cable.
  2. Turn on the miner, connect to its IP address, and ensure it begins hashing .
  3. Place the heat exchanger into the hot tub. If extra heat efficiency is desired, add some insulation to the tubing and around the outside of the reservoir. This is all a work in progress. Substitutions of better products or ideas are encouraged but most importantly, be safe. Safety is always #1 priority!

Step 16: Final Walkthrough

Step 16: Final Walkthrough

Part 4: Testing the Hot Tub

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: 

  • Miner: 835w (set at 800w)
  • Recirculation Pump: 10w
  • Internet: less than 1w
  • Hot tub pump: 40w (this is the recirculation pump built into the hot tub that runs continuously, not the heater) 

The Results: 

  • Running just the hot tub heater...

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. 

  • Running just the miner...

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.

You can view the changelog also in our documentation.
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About Braiins

Bitcoin mining software company: Braiins Pool, Braiins OS+ & Stratum V2.

By miners, for miners.

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