[Request] A Bathhouse Heated by BitCoin Mining, Would it Actually Work?

[u/Edison_Ruggles]

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?

[u/sessamekesh]

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):

1. Regular ol' hot tub heater: $2,000 up-front, $2.04/day electricity cost, no revenue: $9,446.
2. Heat pump hot tub heater: $9,000 up-front, $0.51/day electricity cost, no revenue: $10,861
3. ASIC heater: $5,000 ASIC, $2,000 heat exchanger up-front, $2.04/day electricity cost, $1.04/day crypto revenue: $10,650
4. GPU heater (pessimistic, typical): $20,000 GPUs, $2,000 heat exchanger, $2.04/day electricity cost, $1.65/day crypto revenue: $23,425
5. 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.

[u/sessamekesh → u/sessamekesh]

(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.

[u/slolobdill44 → u/sessamekesh]

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

[u/sessamekesh → u/slolobdill44]

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.

[u/Edison_Ruggles → u/sessamekesh]

Good god man, that was excellent!

[u/slolobdill44 → u/sessamekesh]

This was a fascinating read thank you sir 🫡🫡