I don’t, but I do have a write up with some tips and a parts list if you get back into it. Parts list in the conclusion.

quoting
naddr1qq…2ggj

Intro

When I first thought I might want to build an ASIC space heater I began searching for resources about the process. I found many blogs from companies about testing of different components and lots of other information from individuals dispersed across the web. I never found a resource that adequately answered all of my (basic) questions from point A to point B. I am compiling everything I found here along with my own opinions in hopes that it helps at least one other person. I will try to organize the sections clearly so you can jump around as needed.

A quick note: this guide focuses on the Bitmain Antminer S9, but I will throw in a few pointers or comments where I see differences or opportunities for experimentation with the S19, mainly around lessons learned about fan selection

A few examples of questions you will find an answer (not necessarily the only one) to in here:

1. Is this going to be profitable? Should I do this?
2. Which miner should I buy?
3. How should I modify the hardware for home use and how much will it cost?
4. How should I best use the software to heat my home?
5. How loud is it?
6. Can I control it remotely or connect it to my smart home?

Profitability

Is this going to be profitable

There are many reasons you might want to embark on this project. You may want a hands on project to learn about mining. You may want to use your waste energy to “mine your values” and effectively make non-waste miners less profitable (h/t Resistance Money) (thetrocro (npub1n3s…te5l) and resistancemoney (npub1yez…awc7)). You might want a way to get non-KYC bitcoin. Of course we would all be happy to make a profit. In all likelihood you are unlikely to make a profit if you are not considering your energy costs as a sunk cost. If you are then it may be a borderline proposition and will depend on many factors that will be different for everyone?

1. What type of heat are you replacing? Electric or gas? Which one costs more?
2. How often will you be running it? Can you make it quiet enough to run in a bedroom at night or will it only run for a small portion of the day?
3. How much does the ASIC cost and how efficient it it?

A note on profitability: each miner will have an advertised W and TH/s limit that you can use to estimate J/TH. For this project we are effectively assuming an electrical cost of 0 cents per kWH. With this info you can easily calculate the very rough pay off period for each miner at different hash prices. Further, if you know your electricity costs you actually estimate the break even hash price for each unit. If you are interested in maximizing the efficiency from your project from the get-go I recommend following Kaboomracks (npub1q4z…tv7q) and tracking some used miner specs/prices. Running some of these sensitivities made the current used S19 prices look very attractive as a heating solution. Maybe I will share a future post with this simple calculations, but if you want help in the meantime feel free to DM me.

Should I do this?

I can’t answer this questions for you, but I can tell you that I live in Central Idaho and I expect to receive about \(50-\)80 USD in sats by the end if this winter. My final hardware cost of my build was about $225. My base case is that I will make even less next winter after the halving and with continued decreases in hash price (the dollar value received per hash). Of course, the long term profitability will also need to take into account the future price, which is unknown. If my earnings from this winter double after the halving then I will likely be in profit after 2 years.

For me, this is somewhat irrelevant as I didn’t expect this to end up being profitable. I am happy to be learning about mining, getting some satoshis, and we now have a new small space heater that makes a great conversation piece. It has made me think more about stepping up the efficiency ladder to a larger rig like the S19 and attempt a larger heating overhaul, but I plan on re-evaluating that at the end of this winter.

Which miner should I buy?

The common advice across the internet is to buy a variant Bitmain S9 (with the APW3++ power supply) for some of the following reasons:

1. It is cheap, which is good since this isn’t likely to be the most profitable venture (as I mentioned above)
2. At it’s max it puts out a similar amount of power to a standard space heater at ~1000 to 1500 W
3. It runs on 120 V standard american outlets without you needing to do electrical work or buy extra hardware like the loki kit
4. You can install Braiins OS (comes pre-installed from some suppliers), which will autotune your hash boards for maximum efficiency and let you run the miner at a power target instead of a hash rate target

I purchased a Bitmain Antminer S9i with the power supply and cables for \(102 dollars and the additional hardware will run me about another \)100. After all the research I have done I would consider doing this same project with a used Bitmain S19J Pro 96T (~2,800 W) for about $900, which would mine more sats per W and heat a larger area of our home.

The S9 puts out a good amount of heat to heat a small bedroom or office, but it does struggle to keep the heat up in significantly larger areas even at higher power settings. If you want to heat a living area you might consider looking into a larger unit like a used S19 - I haven’t done this but will provide a few of the things I’ve learned along the way that should translate or where it would be different.

The ability for the S9 to run on a standard outlet without extra work is great for this small project and Braiins has made the software side extremely easy. My machine consistently outperforms the Bitmain specs in terms of efficiency and the interface is easy to use. If you do choose to embark on an S19 project, make sure you look at Pivotal Pleb Tech’s loki kit and their Njord Cloudline, which we will touch on in the fan section.

Using a Bitmain miner allows you to run Braiins OS. There are other autotuning software that may be easier to use, but it’s worth noting that most software (including Braiins) will take a % cut as a development fee - Braiins waives that fee if you use their Braiins Pool (Slush Pool), which also has the added benefit of supporting Stratum V2.

Hardware Modifications

If you want to build a space heater it needs to be portable and not scream like a banshee. Those are the two minimum requirements. There are a few other things to consider, but the bulk of our discussion will be around the cooling options.

Note that the CryptoCloaks (npub1lrj…zvrj) Space Heater Guide has some great information and pictures regarding connectivity and fan replacement. My final recommendation is slightly different than theirs, but I found myself using this PDF a lot during my research.

There are a few things you will need - they each have their own section below:

• A wireless adapter to make your miner portable
• A replacement fan for the power supply
• Replacement fan(s) for the miner
• A mechanism to attach the new miner fans
• Other accessories

The Wireless Adapter

I was lucky and already had a wireless adapter sitting around that I was able to use for my space heater. Mine is a simple range extender I had lying around, and the CryptoCloaks guide has some additional recommendations.

I have not yet managed to consolidate my space heater to a single plug, but that is on the to-do list. I am surprised there is not more info on the topic… so if you have ideas please let me know.

The Power Supply (PSU) Fan

This is relatively straightforward. As CryptoCloaks recommends, I bought the Noctua NF-A6x25 FLX and an adapter (you can DIY this connection but I didn’t try) for about \(23 total (\)15 fan and $8 adapter).

The PSU fan is loud for it’s size so this is a no-brainer upgrade.

The Miner Fans

Here is where it is easy to become overwhelmed with options.

The first topic I want to address is the choice between using a single “inline” fan like the AC Infinity Cloudline S6 versus a traditional computer fan like the Noctua NF-A14 iPPC 3000 (140 mm). After doing research I don’t think there is any denying that the Cloudline fans will more efficiently cool your miner at reasonable volumes. However, there are two major problems with this set up specifically for the S9 (spoiler: none of this holds true for an S19 build):

1. The fan itself is expensive. You will spend about \(120 on this fan versus \)60 total for the two Noctuas
2. If you want to use Braiins OS auto-tuning to it’s full capability you need to purchase the Njord Cloudline and additional adapters to give fan control S9 (not needed for S19), which will set you back about $65

Given the low cost of the S9 the Noctua fans keep project costs within range of what most hobbyists will want to spend and I believe give the 80-90% solution for a much lower cost (~\(60 vs ~\)180 extra) before even discussing how the fans will be attached.

Attaching the Fans

I spent a lot of time exploring the endless options of fan combinations and potential attachments.

So that I don’t bury the lede… you know what worked best for the 140 mm Noctuas? Zip-ties!

In my final build I have replaced these with bungee cords to make them look better, but this simple solution actually cooled more efficiently and produced a more quite result than using fancy adapters.

After a lot of reading I opted for the larger 140 mm Noctua fan, which is available up to 3,000 rpm as the Noctua NF-A14 iPPC 3000. This fan moves a lot of air and is extremely quiet at about 1,200 RPM. I tested the following configurations at 700 W (~9 TH/s). All configurations had the front faceplate removed from both sides of the miner to increase airflow:

• 2 fans attached with a zip-tie or a 36 inch bungee cord (~$65 total)
  • This was supposed to be a temporary configuration until I had adapters. The miner is able to run at 700 W, with each fan running at ~1,200 RPM and the fans sound normal
• 2 fans attached using CryptoCloaks 140 mm Fan Adapters V2 (~$80 total)
  • At 700 W each fan ran closer to ~1,400 RPM and the sound profile seemed different. I am unsure if this is caused by air rushing through small gaps in the adapter, by the restricted airflow through the miner, or by cavitation caused by having the two fans running in series with no gaps to let the the fan pull extra air if needed
• 1 fan attached using the adapter and pulling through the miner (~$40 total)
  • This had a more pleasant sound profile since it was just a single fan, but had to run at ~1,600 RPM, which was just a bit too loud compared to two fans at 1,200 RPM. This configuration performed very well closer to 1,000 W as the RPMs only went up slightly as the wattage increased. It wouldn’t work for a bedroom, but would be fine as an office heater

The surprising result here is that the worst performer was attaching both fans with the specifically designed adapter. My best guess is that forcing the two fans to share the same airflow was creating extra vibrations that increased noise and required the fans to work harder to move air. I don’t have another explanation at this stage.

Using a single fan with the adapter is an interesting option if you don’t need the fan to be “bedroom” quiet. Given that the fans are often the most costly part of this build, dropping the cooling hardware costs to about $40 is fantastic.

Caveat: I obviously did not get to experiment with attaching an AC Infinity Cloudline fan since I didn’t buy one, but I think it would be difficult to attach properly without a 3D printed shroud of some form. As stated above, I would consider the Cloudline for an S19 build at which point I would have less hesitation to spend \(30-50 getting a proper shroud for a ~\)1,000 heater.

Other Accessories

You might consider a few other things - below are some miscellaneous notes that might be helpful.

• Fan filters - I tested using a coarse fan filter on the intake to block debris. This was cheap, but did add about 150-200 RPM at a given wattage. Given that I am going for a quiet build I opted to not use these filters. Having the fans attached via bungee cord makes it easy to open and clean the miner frequently.
• Fan grills - I did buy a set of replacement 140 mm fan grills to protect the blades and anyone near the heater. I managed to shatter a Noctua fan blade when tightening a zip-tie near the fan so I highly recommend installing these as they don’t disrupt the airflow at all and are relatively cheap.
• A case - I have not yet invested in a case. Given what I now now about how these fans can be best attached I am tempted to build a very simple wood enclosure, but for now I simply have the PSU zip-tied to the bottom of the miner. It doesn’t look the best, but given that I don’t have a 3D printer, I am not ready to shell out $150+ for a case and am not even sure a case like the CryptoCloaks design would be conducive to my build that doesn’t rely on adapters.

Software Settings

I personally found the “settings” section of the CryptoCloaks guide very confusing. I think these are likely generic settings that don’t assume you have access to the Braiins software. Since this is an S9 guide for beginners I am going to assume you are using Braiins.

Braiins allows many configuration options and admittedly, some of the operations (like the auto-tuning) are not very well described. In short, you can either manually configure the settings for your boards and fans or you can tell Braiins some max temp settings and how much power you want to draw and it will decide the rest. I have had the most success relying exclusively on the auto-tuning and I run my target temperature slightly higher than the default (at 94 degrees C) so that the fans can work a little less making the device quieter.

Optionally, you can specify a maximum fan speed instead of a target temperature and Braiins will control the wattage to ensure that you don’t surpass the hot temperatures. I am admittedly not sure how this works with the auto-tuning and have preferred to lock the target temperature and allowed the fan speed to fluctuate - generally the fan speeds stays quite stable once tuned for a given wattage.

A few general tips that I got hung up on and needed to research in no particular order:

• Each power setting (wattage) must be auto-tuned separately - the profiles for each wattage are saved in the device memory and can be cleared, but it requires a command line interaction over SSH. It can take hours (on average for me 4-6) to tune a single wattage. I have tuned mine on every 100 between 600 and 1,200 W, though I typically operate in the 700 - 1,100 range. Sometimes the device will decide to adjust tuning on a setting. This can change the sound slightly when you don’t want it, but it is typically less noticeable than the changes during the initial tuning process.
• As far as I know there is no way to disable the LEDs on the control board - I will probably buy some liquid electrical tape to cover them.
• There is no way to disable the fans running at 100% speed for a few seconds as soon as the miner is turned on. BitcoinTalk forums indicate that this is something related to the Miner BIOS and cannot be adjusted by software - I don’t know how true that is. It makes turning it on or changing settings in the middle of the night difficult, but it is what it is.
• Don’t bother with the dynamic power scaling settings they are a rabbit hole that you should likely just avoid unless you know some use-case for it that I haven’t found.
• You should turn on immersion mode - all of your fans will still work the same, but it avoids some buggy behavior in Braiins that is common with non-stock fans. This manifests as the fans sometimes running at 100% when the device is turned on and the machine never starts hashing. Source

How loud is it?

Time for some data! There are a few different ways to track these data. I try to roughly get decibels using an iOS app, but the easier way to track is to see the trade-off between the stable RPMs at a given wattage using Braiins.

Below I provide RPM and decibel data for my optimal set up (2 Noctua 140 mm attached with a bungee cord) at various wattages from 700 to 1,100. My wife and I are comfortable running this set up in our bedroom at 700 watts at night and 1,000 - 1,100 during the day in our living room. 600 and 1,200 watts did not deliver very good results with Braiins auto-tuning and so I have kept the scope of this data within that range. A quick Google search suggests that a reasonable decibel level for a bedroom is 30-40 dB. You can immediately see why anything above 1,200 RPM per fan becomes a problem.

TH/s	W	RPM per fan	approx. dB	J/TH	Expected Sats per hour*
9.02	700	1,140	39.7	77.61	82.68
10.35	800	1,360	43.2	77.29	94.88
11.6	900	1,440	44.5	77.59	106.33
12.45	1,000	1,620	47	80.32	114.13
13.42	1,100	1,760	49.6	81.97	123.02

*estimation assumes a hash value of 220 Sats/TH/Day

https://image.nostr.build/0b9054943416be605dc0cd7400ed7b90cd41d5e253e713052effc3c9983ea39c.png

Another nostr user, ben (npub1000…7nql), provides another helpful comparison of his stock S9 running Braiins at 700 W. The stock fans are 120 mm and are firmly attached to the opening of the miner, unlike the zip-tie method. He reported higher RPMs and higher decibels than what I see with the zip-tied 140 mm fans as seen below:

note1ahg…f9v6

Clearly the Noctuas are doing their job!

Unfortunately, I don’t have good decibel measurements on the 140 mm fans with the adapters, but given the higher RPMs and generally improved sound profile of the “premium” Noctuas over stock fans I would expect it to fall somewhere in between.

Remote Connectivity and Smart Home Integration

This is a bit of it’s own rabbit hole, but I figured it’s worth mentioning. Since this set up is independent of an HVAC system it is nice to have a way to control it from other devices.

Generally, I connect to the dashboard via the web interface from my phone but I also wanted to be able to track the data against temperature and heating data from the Nest that we already have in our home.

Through this ended up installing Home Assistant OS on a raspberry Pi I already had lying around. I was then able to connect the S9 using this HACS plug-in. I would say there is a significant learning curve to get this all running smoothly, but it provides fantastic access to data and home automations using presence or other device data without relying on a cloud provider. If I end up running a larger S19 system I will certainly use this to sync my Nest thermostat any cycle the miner on and off before kicking on the central air.

Conclusions

This has been a great personal project for me that started with a focus on learning about bitcoin mining and has morphed into a project that changes how I am looking at my home efficiency.

Below is the total cost of the parts included in my final build:

• $102 Bitmain Antminer S9i from @kaboomracks
• ~$25 WiFi adapter (I already had this)
• $15 Noctua NF-A6x25 FLX
• $8 PSU fan adapter (you only need one from this 2-pack)
• $60 2 x Noctua NF-A14 iPPC 3000
• $7 140 mm fan grills
• \(3 bungee cord for a total cost of ~**\)225**.

https://image.nostr.build/c466e84095c4172ecca083bcb53bc17c939a145c9ea39ebe191f89496d199002.jpg

My primary goal here was to compile my learnings in one place, but I think this process revealed a few key takeaways that I hadn’t seen elsewhere:

1. If your goal is balancing cost and utility you should probably only consider the AC Infinity Cloudline fans if you are doing a larger S19 build since this fan and controller will likely add about $120 in cost for an S9 build.
2. If you want to go really cheap you can probably get away with a slightly louder, single Noctua fan, but you won’t want to use it in a bedroom. This will shave about \(25-\)35 off the cost depending on whether or not you buy the adapter
3. Noctua fans without a specialized plastic adapter reduces cost and increases performance (same power, less sound).