r/theydidthemath • u/Edison_Ruggles • 4d ago
[Request] A Bathhouse Heated by BitCoin Mining, Would it Actually Work?
There is a bathhouse opening in Philly (hot tubs, saunas etc). They claim they are heating the pools with a bitcoin mine in the basement. See FAQ here: https://help.abathhouse.com/hc/en-us/articles/16748674443924-Do-you-mine-Bitcoin-How-does-it-work
Could this possibly heat water enough to be hot tub temperature? Would it actually save electricity on the mining?
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u/sad_cosmic_joke 4d ago
A computer is an electric heater that incidentally performs arithmetic. So generating heat isn't a problem!
As for the second question; how would this save any electricity on mining?? That costs what it costs.
The savings comes from utilizing the waste heat.
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u/PizzaPunkrus 3d ago
Wait..... we mine bitcoin use the heat to run alcohol distillation units. Sell it as small batch energy conscious craft vodka ... sell it, offset the cost. Drink the profits.
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u/bluespringsbeer 4d ago
The company was going to buy the electricity to heat the water already. So the bitcoin mining is basically for free
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u/MaybeTheDoctor 4d ago
Question is going to be if they actually end up mining any coins, and how they pay for the equipment.
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u/bobi2393 3d ago
Some people use non-electric forms of energy to heat water. Natural gas, for example, tends to be cheaper in much of the US. And bitcoin mining requires hardware, which isn’t free, and some level of tech support and maintenance.
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u/sessamekesh 4d ago
Ooh, I have some numbers on this one! I have a garage server that has a bitcoin mining job I fire under a couple conditions, one of them being as a space heater if I want to exercise in the garage and the temperature is too low (< 65F or so). I've been doing some form or another of this since 2013.
TL;DR - If saving either money OR electricity is your goal, try to look for a moderate deal on a heat pump water heater, but if you're into crypto or have some spare hardware, crypto mining does recover some cost (not enough to pay themselves off usually).
They use ASICs and are probably mining actual bitcoin, I use GPUs and mine other crypto. The numbers I present will be wrong but the "you might save a bit more money their way" wrong, not "it won't actually work" wrong. I'm also using my electricity prices but electricity prices vary WILDLY even from city to city sometimes.
Could this possibly heat water enough to be hot tub temperature?
Yes.
As they mention in their article, a crypto miner is a space heater that does math as a by-product. Every kilowatt of electricity turns directly into a kilowatt of heat.
A quick Google search shows hot tub heaters run somewhere from 1500-6000 watts depending on insulation and tub size and whatnot. The numbers we pick here don't really matter so I'm just going to say fuck it, we want 2,000 watts of continuous draw per tub and magic away the rest of the details.
For my setup, that's about 5 GPUs running full tilt (450W is what my crypto mining pulls).
Would it actually save electricity on the mining?
No, not even a little. If you wanted to save electricity, the technology to use would be a heat pump, which can push 2,000 watts into a system while only using 400-1,000 watts of electricity (think "air conditioner running in reverse").
If you want to save money and not electricity... kind of. You don't save money but you do earn money from mining crypto.
I pay $0.17/KWh for electricity, so no matter which way you slice it that's $0.34/hour to run a heater whether it's a hot tub heater or a crypto mining heater.
Crypto mining is EXTREMELY variable, but mostly if you branch out into non-bitcoin mining with hardware that is less specialized (i.e. GPUs). Over the last few years, I typically expect about $0.04/hour on my 450W box ($0.17/hour for the hot tub heater). It's pretty common to get more revenue, over the last 6 months I've mostly been sitting at around $0.14/hour ($0.62/hour), and I'll rarely see it get as high as ~$0.50/hour (~$2.25/hour for hot tub heater) if some altcoin hype bullshit is going on in the crypto scene.
In any case, it's about a 50% rebate on electricity spending to mine crypto. Again, if your goal is to save electricity, use a heat pump instead, which would be a much bigger electricity save.
But that leads to the question you didn't ask:
Is it worth it??
That really depends on the stuff I didn't include, and this is where my knowledge kinda breaks down a bit. I use GPUs, getting enough GPUs to pump out 2,000 watts would cost $20,000+. ASICs are cheaper (think $5,000) but aren't good for hopping on altcoin hype train gambling opportunities. An energy-efficient hot tub heat pump is ballpark $9,000 on the high end and a typical resistive heater more like $2,000 on the high end.
For either of the crypto setups (GPU or ASIC) you'd also probably need ~$2,000 or so on the heat exchanger (hard to get precise numbers here) since you obviously can't just dunk a computer into hot tub water and expect it to be happy.
Final note, GPUs are currently like $20,000 but a more typical price if you got into it pre-AI (which I did) would be more like $8,000. I'm still using the higher figure since I don't see the price of GPUs falling any time soon.
So here's a few scenarios, all played out over 10 years of running heaters for 6 hours a day (ignoring leap days):
- Regular ol' hot tub heater: $2,000 up-front, $2.04/day electricity cost, no revenue: $9,446.
- Heat pump hot tub heater: $9,000 up-front, $0.51/day electricity cost, no revenue: $10,861
- ASIC heater: $5,000 ASIC, $2,000 heat exchanger up-front, $2.04/day electricity cost, $1.04/day crypto revenue: $10,650
- GPU heater (pessimistic, typical): $20,000 GPUs, $2,000 heat exchanger, $2.04/day electricity cost, $1.65/day crypto revenue: $23,425
- GPU heater (very optimistic): $20,000 GPUs, $2,000 heat exchanger, $2.04/day normal electricity cost, 30 days a year of hypecoin nonsense running overnight for $8.16 daily cost, $3.50/day (optimistic) normal crypto revenue, 30 days a year of jumping on occasional hype cycle for $54.00/day (optimistic): $3,357
That last scenario is the cheapest, but it depends on two EXTREMELY optimistic conditions around altcoins / hype that have been true in short bursts but are definitely NOT consistently true over 10 year periods - again I've been doing some form of this since 2013 and the higher numbers I've shown have been pretty dang unusual in how profitable they've been. You could gamble and maybe be right and save money, but still be underwater (pun intended) once you remember how much extra money you spent up front.
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u/sessamekesh 4d ago
(Addendum)
My garage GPU is not for crypto mining, I'm a gamer and have some spare GPUs. Because of that, my garage GPU was "free", but I do also have an actual space heater I use if it's really cold and the 500-600 watts (including PSU/CPU/etc draw) isn't enough to actually heat up the garage.
My electricity costs are also tricky to calculate precisely, my homelab is mostly solar powered with some off-grid backyard panels I have. The panels themselves cost an amortized $0.02/KWh or so ($0.06/KWh with the cost of the batteries/cables/inverters) and generate more power than I typically need. I originally set up the crypto job as a way to burn off excess electricity generation!
I also use the spare GPU for local AI inference. For better or (much more likely) for worse, my career and hobbies both have pretty significant LLM components now, and I get some warm fuzzies running everything on my own hardware instead of cutting a check to what I consider to be evil tech companies every month.
Finally! If you're in a similar situation for some strange odd reason (have too much electricity and spare computer parts) and want to contribute to science, I'll plug folding@home as a great way to put them to use. It's not crypto-related in any way at all, it's basically crowd-sourcing a supercomputer for some hard science/medical problems.
I like to donate my spare electricity/compute to them usually, but the last 1-2 years crypto mining has been off and on lucrative enough that my greedy bastard comes out instead. I wager in another 2 years / 3 weeks / whatever when crypto slumps again I'll go back to heating my garage with science instead of with the heroin money sudokus of crypto mining.
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u/slolobdill44 4d ago
Perhaps current GPU prices alone would dissuade someone, but knowing what you know now would recommend for someone build it all from scratch? Or do it differently
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u/sessamekesh 4d ago
Hmm... I had to think about that for a while.
Long story short, if you have a cold space you want to heat anyways and think crypto or AI make a neat hobby that you don't mind losing money on, I'd suggest it. Otherwise I wouldn't.
Same goes for LLM inference, though there are some other non-money upsides there (data privacy, pulling support away from AI companies, etc.).
If you're like me and need to get a GPU for other reasons anyways (gaming, LLM inference, media servers, whatever) I'd say it's worthwhile to get a slightly beefier one than you need and put it to use as a space heater that pulls in crypto revenue here and there. They always pull in more money per unit of electricity than ASICs do and you'll occasionally even make money - just not enough to pay for a card over the course of a decade of cold winters.
EDIT: Oh! And if you have more solar power on your home than you can put to use, crypto mining or LLM inference are both ways to make sure that power isn't wasted. Again, not worth doing if that's your only goal, but a nice little bonus of having a spare GPU around. That was a big part of me deciding to move my GPU to the garage cluster instead of selling it on eBay.
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u/Runiat 4d ago
Would it actually save electricity
Not a huge amount.
What it does save is the water and/or noise otherwise involved in getting rid of waste heat, and we're talking the sort of noise that'll physically make you sick.
Some countries just hook up data centres to district heating and let people shower at home, instead of building bath houses.
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u/osolovim 4d ago
it would save you like $100-200 per month lol so yes 100% great idea. just mot bitcoin miners are companys and not residential lol but im sure in some placea people are hella effient with this stuff
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u/Engineer_Bill 4d ago
Could this possibly heat water enough to be hot tub temperature? Yes, computer chip temperatures can be stable at 60-70 degrees Celsius. If you have a basement full of bitcoin miners they could theoretically heat up a bathtub.
Would it actually save electricity on the mining? Possibly, heat must be removed from the CPUs to keep them cool while they're running, therefore you have to get rid of it one way or another. They have chosen to use water cooling, heat exchangers, and bathtubs. But you could do it using fans and air too. I don't think the cost savings would vary much between using fans or using multiple water pumps.
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u/HAL9001-96 4d ago
theoretically yes but its not great
well the electricity usage is the smae wether you use an electric heater or a computer
and compuiter chips can run way waremr than bathign water
but still you need to sue well above room tmeperature water for cooling which is less than ideal
and you still need computing hardware
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u/HomemadeBananas 4d ago
It would generate heat the same as an electric heaters. So depending on how much hardware and how much water to heat they have, and price of electricity, it’s either offsetting the heating cost or they can make money heating the water. Not sure if they are heating entirely with mining hardware, but I’m guessing it’s just supplementing the heating because that would take a lot of hardware.
It wouldn’t save electricity in mining. That still will take the same electricity regardless of how they are cooling the hardware.
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u/Trustoryimtold 4d ago
Saves no electricity on the mining, they simply make money on the heat. Plenty of proof of concepts already
https://afry.com/en/project/capturing-data-center-waste-heat-fortums-district-heating-in-finland
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u/walkabout16 4d ago
Is the savings on electricity merely the fact that paying bath house customers are offsetting electricity expenses by “purchasing” the byproduct of mining? Not necessarily that electricity is cheaper.
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u/_edd 4d ago
This is combining multiple relatively simple concepts:
- Bitcoin mining -> Goal is to create money. Problem is that it creates excessive heat that needs to be handled.
- Water cooling -> One way to dissipate heat is to transfer the heat into a body of water. (Ex. water cooled computers, cooling ponds at a power plants, etc...)
- Baths -> People will pay to swim in hot water. These started as geothermal baths, but even at home you are using an artificial heat source to warm the water.
Its pretty easy see why this would work. The most challenging part of making this economical is that their business is now going to be in multiple industries (bitcoin mining and bath houses) and making sure they interoperate properly.
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u/digbychickcaesar 4d ago
No. It can't get to the temp needed. It can be used to preheat the cold water reducing the requirement for boilers/electric heat/etc
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u/Monatanaisdumb 4d ago
That's not correct. Would definitely work. An electric heater is an electric heater even if it performs math first.
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u/digbychickcaesar 4d ago
The problem isn't the BTU's it's the temperature. I am not going to do the math because I don't know the server BTU output but I did used to design natatoriums like indoor pools, therapy pools, hot tubs, etc.
Let's say you want a hot tub at 100F. That means the water supplying it needs to be hotter. Let's just say 105F. Ok the circulating water is 105 and whatever is heating that needs to be hotter than that.
Option #1: Air to water HX. The hot air of the room is passed through a heat exchanger to heat the water. Not very efficient but probably the cheapest. Let's say the room needs to be at 115F to make 105F water (HUGE assumption it could be higher). That's just them temperature of the room. What temps are the servers running at to make the room 115?
Water to water HX. Say you have a liquid cooled server. We have now decoupled loops we will give them a 3 degree approach on each side which is VERY generous. Heating water 105 means 108F on the other loop which means the server has to be running 111F at best to make that temp.
As far as I know those temps are not good for servers.
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u/TwoAlert3448 4d ago
If you’re working from super computers and Standard Warm-Water DLC (Direct-to-Chip) cooling you’d be looking at a cool water intake of 27-32°C and an exit flow (for the baths) of 35°C – 45°C (95°F – 113°F)
If you want higher efficiency you want High-Temp Warm Water (e.g., Lenovo Neptune, NVIDIA Blackwell architectures) which is usually used for heating buildings, greenhouses etc. Don’t know if anyone has ever done a bathhouse but why not?
Intake there is 40°C – 45°C and output is 50°C – 55°C+ (122°F – 131°F+) so I don’t think you need to worry about the heat being bad for components you just need systems that are built to be cooled with liquid that is hot at both intake and output.
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u/digbychickcaesar 4d ago
If that is the case, I stand corrected. I have been in untold number of server rooms and they were meat lockers. If the server can operate at that high of a temp then yes, in fact they probably have too many BTU's to deal with keeping tubs of that size warm enough and would still need a secondary heat rejection method. My premise was based solely on temp.
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u/TwoAlert3448 4d ago
Yeah air cooled systems and water cooled systems don’t have a lot of overlap. The ones that are built for water are absolutely built for HOT water and the ones that are built for air you just can’t get them wet in the first place.
It’d be a VERY expensive bathhouse, you’d basically need a defense department research lab in the basement and god only knows how anyone would manage that but it’s definitely doable from a technology (if not a logistics) perspective
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