Interview: Home Immersion Bitcoin Mining

This piece is part of a series that features interviews with Bitcoin miners about their experiences setting up and scaling mining operations, as well as their views on the direction of the mining world. If you are mining Bitcoin and want to share your knowledge and story — the ups, downs and innovations — reach out to the author on Twitter @CaptainSiddH.

For this interview, Coin Heated spoke about his massive, 2.4 petahash home bitcoin mine. Nearly all of his machines use immersion to reduce noise and improve heat reuse and miner reliability. Coin Heated is now commercializing a unique line of tank designs called the Hotbox, with the first production tank being the Hotbox Liu, which is specifically engineered for six S19 ASICs. You can find Coin Heated on Twitter (@CoinHeated) and YouTube (Coin Heated).

Thank you for joining me today, Coin Heated! Before I jump in to specific questions about your mining setup and immersion system, can you tell us the story of how you got into mining and how you achieved the scale you’re at today?

I first started mining Bitcoin in 2010. My friend said I should look into it, and since I’ve worked in IT for a long time I had some extra computers around, I thought I would give it a try. Mining was still possible with a CPU at this time, though graphics cards were starting to take over. I spent a few days mining and when I was done, I think I had about 12 cents worth of bitcoin. I thought, “This is a waste of time.” Then I watched bitcoin go to $100 and thought, “Woah, I missed the best time to get in.” Then it went to $1,000 — again, I thought I missed it. I always thought I missed the best time to get in over and over again. Last year, I finally said I don’t care. I’m all in.

I bought an S9 on eBay and they shipped it with absolutely no packaging at all. None. They just tossed it in an empty cardboard box and sent it. The fans were all beat up and damaged, so I sent a message through eBay about that and the seller just refunded me without wanting the S9 back, so I got a free machine. I bought that S9 to replace an electric space heater in my workshop, because I thought the space heater was a 100% waste product device — sure, it makes heat, but an S9 pays me to make heat. As soon as I confirmed the S9 was actually paying me while heating my workshop, I was hooked, and knew I needed to scale up.

I ordered nine more S9s, and then made the leap to my first S17. Then a bunch more S17s followed not long after that. Now I’m up to 28 ASICs, all a mix of S17+ and S19. The most power I’ve drawn was a bit over 70,000 watts, which is somewhere between 250 and 300 amps of power. All summer long, I heated a 17,000 gallon swimming pool. I downsized the pool for winter because I knew I would be moving, and because there was a small leak in the big pool.

How does that power draw compare to the rest of your house?

It’s almost incomparable. The biggest energy users in my house are an electric dryer and air conditioner — you might have 40 amps from one of those, compared to 250 to 300 amps from my miners. I have a 400 amp dedicated service and meter just for the miners, and then I have a regular 200 amp household service. A couple of days before the technicians came to set up that dedicated service, the transformer on my block blew out. At that time, I was running very close to the 200 amp max. load on my regular home.

The power company came out and I told them I was drawing like 180 amps 24/7 here. They told me that can’t be it — it has to be some institutional-sized draw. I told them I’m bringing in 400 more amps to my house and they said it would be no problem. Over the course of ten days, the power went out six times, until they finally replaced the transformer on the pole. That lasted a few more months, and then it blew out again. They just replaced the transformer again, saying it was simply a bad transformer.

What was the process to build out that 400 amp dedicated circuit?

It really wasn’t bad. I just called up Xcel, the power company in Minnesota. Here in Minnesota you can only have one power meter per building, but I have a detached garage which counts as a second building. I think the total hookup cost from Xcel’s side was $400, though the total cost was about $6,500 after having an electrician come out and put the panel in place.

Better yet, once I got that new circuit, I could prove that I had a load larger than 50,000 watts which allowed me into a special program from the power company. Prior to the special rates, the largest power bill I ever had was around $6,400 — almost equal to the circuit installation cost. However, the month after I installed that circuit my bill dropped significantly. So the savings were very well worth it.

Description of a demand response program deployed in Australia, similar to the one available to Coin Heated in Minnesota. Source.

The way that power program works is the power company asks you to cut a minimum of a 50,000-watt load within a specified time over certain days during the summer, to help them load balance the grid. In the agreement, there is a maximum amount of time I agree to that I must power down. I showed the power company that I can power everything down except for the switches, which is maybe a few amps at most, and they were good with that. The offset in power cost greatly outweighs the lost revenue from downtime. I have to be down for two weeks in the hottest period of summer, and in return I get a solid discount. I’ll take that.

Do you run your miners through an LLC or business entity?

That’s why I originally started Coin Heated LLC last year, to start tracking expenses and offsetting costs. In 2022, the income is off my personal taxes so it doesn’t change my tax bracket. If you get into scale, owning a business allows you to write all that power consumption off of your profit. Even if you don’t do anything else other than expenses for that, it’s still worth it. Obviously with one or two miners, it’s not going to be worth incorporating a company, but once you’re getting into 20, or 30, it makes a lot more sense to subtract your costs from your revenues before paying taxes.

I want to go back to when you just had one S9. You mentioned when we were chatting earlier that you had a 6,500-watt space heater before the S9. How did the heat output versus the energy use compare between those two?

The space heater would come on and off, heating the room very quickly then shutting off when its thermostat detected the right temperature. The S9 wasn’t as powerful, but I ran it 24/7. It averaged out almost the same. That S9 heated the workshop well enough that I thought, “Okay, this makes sense.” I was running it at a breakeven cost, but it taught me everything that I needed to learn about ASICs and Braiins OS+, and it allowed me to test immersion.

Let’s talk about immersion. I know you’re using immersion and repurposing the heat. Was there a reason you used immersion rather than just air-cooling and redirecting that heat to your home?

When I had just one S9, at full power it was very loud, and that was annoying. It’s about as loud as a shop-vac running. I started looking into how to deal with the noise and I discovered immersion. I knew about immersion before I was ever into Bitcoin from overclocking regular PCs — so I’m familiar with liquid cooling in general. Once I discovered that you could do immersion with ASICs, that just opened up everything. Once you have it in a liquid, you can pipe that heated liquid around much more efficiently than you can air. Plus, the noise is almost non-existent.

Where do you get the dielectric oil from?

There are a few places that make it. Engineered Fluids makes BitCool. They’re just one of the first people I found that were highly recommended. What I liked about them specifically, is they have a massive amount of online information about compatibility — different materials that work or don’t work. It’s definitely not the only solution, but it works well and I really appreciate the amount of time and effort they put into making all of their data available online.

Most dielectric oil is said to have about a 10-year lifespan, and it doesn’t evaporate. Your only factor is contamination, so if it’s closed and there’s not all kinds of dirt and contaminants getting in there, it really should just do its thing. It’s not like car oil where you have combustion and it’s burning off so the oil must be replaced often.

So how did you make the decision to heat your pool?

The miners actually came before the pool. I had maybe four S17s in a fish tank with a car radiator on top of them. It was functional, but I wanted to get someone with HVAC experience to help me find something to do with the heat.

These HVAC guys who usually work on multi-million-dollar homes came out to my little workshop to look at this contraption with a car radiator on top of a fish tank held up with two by fours. They gave me some ideas of things they heat that I would not have expected at first — a pool, a driveway, etc. I started thinking, and decided a pool would be excellent, because I’ve got kids who love swimming.

I bought the biggest above ground pool I could find and started heating that. I discovered that the pool actually worked as an excellent heat buffer for the miners. We have some pretty wild temperature swings in a 24-hour period in Minnesota, but connecting the heat of the miners to the pool meant the oil around the ASICs would only fluctuate maybe one to two degrees per day. That really helped out the S17s because they’re extremely fussy about any kind of temperature fluctuation. At only $1,000, the pool was actually cheaper than a dry cooler setup.

Are you drawing heat off to anything but the pool right now?

Not yet, however, in my new house, I will be funneling heat from the miners into the pool and then tapping off of that to some degree, to bring it back into the house and circulate around. Here’s how it will work: The miners will heat the oil in my tanks, which will heat water via a heat exchanger. That water will head to a hot water heater, then to my home HVAC system, then out to the pool. There will be automated valves for the HVAC system so the house can accept or deny more heat depending on the thermostat.

In the summer months I needed a little extra help to get rid of heat. I had a fountain in the pool, which helped, but I also had a dry cooler feeding off the pool to help bring temps. down.

What is your vision for the future of home mining, especially given your many experiments with heating? Would a homeowner who doesn’t care about Bitcoin want to use an ASIC for heat versus just using an electric or gas heating system?

As I think about the roadmap in five to 10 years, if I’m a power company, and my competitor is natural gas, I can offer an incentive to replace your natural gas furnace with an ASIC-powered furnace. It’s likely that a power company wouldn’t directly sell this product, but partner with another company to supply, install and manage them — with the power company being able to have some amount of control over power demand to the furnace. That is, in the summer months, the miners could be scaled back to very low power during high electrical demand.

In Minnesota we already have these “eco saver” switches for air conditioners that are remotely managed by the power company. You basically agree to give the power company remote control of your AC in return for a discount on your power bill, and then the power company has the right to switch off your AC if the grid’s load is too high. The same concept could be applied to an ASIC heating system. All winter long, you want that heater running 24/7 max. power for max. heat. During summer, you can underclock it using Braiins OS+ or some other aftermarket firmware. If the miners are put to sleep, only the control board is powered. I measured it, and it’s only about 1 amp draw compared to 12 to 15 amps during normal operation and up to well over 20 amps in an overclocked setting for S19s. I’ve not yet measured Whatsminers, as there is no aftermarket firmware widely available yet.

The really awesome thing about mining is you can just shut off for a couple of days and really nothing changes. It’s not like a web store server where you’re going to miss orders. You might miss some found blocks, but the cost advantage given by power companies for being interruptible is huge. Plus, almost all of the power going into an ASIC comes out in heat. It’s really close to as efficient as a regular resistance heater.

You’ve acquired a lot of mining machines fairly recently. What advice do you have for new miners on spotting hardware scams?

Never trust, always verify. Seriously. Anybody that makes something super easy and just wants your money right away is almost always a scam. Talk to somebody over the phone if you can. Doing so on video is even better. Verify that it’s a real business you’re working with. Anybody that’s not willing to take a step to actually verify with you that they’re legitimate is probably not worth your time.

You are also working on commercializing your immersion setup by creating plug-and-play tanks — can you walk us through your plans there with the HotBox Liu?

When I started doing immersion, I used fish tanks, and those still work fine, but I started to get obsessed with an actual intentional design. The guys at AIPROPROENERGY reached out to me and asked if I wanted to make some real immersion tanks, so I started making one specific for S19s in a rackable setup. They were ready to go, and so was I, and we formed a joint venture to develop the tanks. Other immersion tanks typically have you remove the fans, require the hash boards to be flipped around, and then the oil is slowly pumped up through the bottom, allowing the rising heat to come to the top. But I was never satisfied with doing what everyone else does.

Proof of concept design for the HotBox Liu, with five S19s inside. Source.

For my design, I left two fans on the “rear” of the ASIC. I then designed my own standoffs to direct the oil down and out, back up through the center through the heat exchangers. This gives a better oil flow with lower temperatures, meaning happier miners. I designed my own standoffs allowing you to just put an ASIC straight down into the tank. Plug it in, turn it on and you’re done. I’ve been running fans in oil for a year now without any failures aside from a specific model fan that fails in a day or two. The fans only spin at about 200 RPM, so the ASIC doesn’t pick it up as “on.” However, I am redesigning a fan blade profile to work more effectively in oil, where the ASIC can register the signal correctly and report on fan failure if/when it happens.

Instead of following the standard of oil flowing up from the bottom and to an overflow, I changed the oil flow to go from top down, following the normal flow of what the ASIC was designed for. Almost everything in the tank I made is completely opposite of what everyone has been doing. It just made so much more sense to me. Everyone knows heat rises, but if you have an oil flow that’s fast enough, heat rising is irrelevant — the flow in my tanks is much faster than the speed at which heat rises in oil.

After the Hotbox Liu enters production, I’ll finish designs for the Hotbox Duo which will not be specific to S19s, and will allow different sized ASICs.

Do you have a timeline for when the HotBox Liu will go on the market?

The design is complete, and we expect production to begin in early February. Initial production will be done in Houston in low volume, but will be manufactured in Russia at existing AIPROENERGY facilities there in larger volumes. We are anticipating a price around $2,900 to $3,500 depending on options, with the lower end having no electrical components like PDUs (power distribution units). The HotBox Liu is specifically designed for S19s only; no other models will fit. It will fit six, but can I have tested it successfully with every combination from one to six. The downside of using fewer S19s is that you either need extra oil or some other ballast.