Should a big external fan blow or suck for mining?

I guess most miners have fans set up on both sides: one blowing air in and the other pulling it out. When it comes to adding a powerful, quieter external fan, what should I consider when deciding if it should push air in or pull it out of the miner? I'm thinking of keeping the original fans on the miner and then either blowing or sucking more air through it until those stock fans hit their lowest rpm, or until the external fan gets louder than the original ones, whichever happens first. I picked up one of these fans and it definitely seems capable of moving way more air than my S9J miner needs: (no need to click the link, it's just ads!): https://www.hyper-phresh.com/hyperfan Here are the main specs: it comes with a speed controller and I can 3D print any adapter to make it fit with the miner. A few specific thoughts I had were: 1) The external fan might make more noise on the exhaust side than the intake side. I did a little test, and the noise seems pretty much the same no matter the direction. So from a noise reduction angle, it doesn’t really matter which side of the fan is exposed to the outside or connected to the noise-dampening duct. 2) The fan might create suction differently compared to how it creates pressure. I haven't figured out how to test this yet, but I'm planning to design the 3D printed adapter so it can attach to either side equally, allowing me to switch it up. 3) The ducting (Seahawk acoustic duct 200mm https://www.benchmarkbioponics.com.au/products/acoustic-polyester-ducting-100mm-x-5m) might also have some impact.

you don't stack a fan onto the stock fans. the stock fans will restrict the new fan if they are slower than the new fan. and the new fan will restrict the stock fans if it is weaker. if you have a s19 there are kits to fully remove and bypass the stock fans and have a more powerful new one.

You are correct, but I don't know if the air flow restriction and resulting increased energy consumption is significant, considering the overall energy consumption by the miner. And then there's the waiting time to get the fan spoofing device to where I am. Definitely maybe later! I want to keep the stock fans in place to avert any issues when / if the external fan fails, or something in my experimental setup goes wrong. I will also quite likely remove the external fan repeatedly in order to experiment / develop quieter cooling setups with other miners. Regarding 3): Collapsing tubing: I tested it, the tubing tries to shrink in lengths and will tear itself off any insecure attachment, but the lumen does not collapse. One less worry.

Turns out you are spot-on. The powerful Phresh fan actually increases the noise levels by spinning up the stock fans to very high speeds. And they seem to excite each other with annoying interference resonance loops. Would it be possible to 'spoof' the controlboard with some small PWM fans that can spin up to say 6000rpm, just until I can get some of the spoofing boards? I suppose I could also leave the stock fans connected to the the control board (but not connected to the miner housing) for now. Just need to fasten them so they don't take off at bootup! Re: Sucking or blowing: Sucking appears much more convenient so far, for 2 reasons: 1) the dangerous intake side of the Phresh fan gets covered with the adapter, less risk of fingers ending up in the fan blades 2) Exhaust hose is easily attached to the Phresh fan to direct the warm air to where it's needed, therefore no 2nd adapter required.

The theory is that sucking is better because you don't add the heat of the fan itself. It also tends to attract more dust because its negative pressure for the miner. So i guess it depends in your actual setup. If its well filtered with noise insulated ducts that reach the outside on both ends, i would go with suck. But if its something like no inlet duct or scooping air from the inside, maybe blow is better. Obligatory reference: With the likes of the infinity 8" you don't need any other fans at all. 800cfm is twice the required volume so it should be fine at 50% or less. PS: I don't like leaving the small fans because they can be forced to generate electricity by the external fan.

let me find the kit I used. https://www.ebay.com/itm/304119146264 if you use braiins you can not worry about the fans at all https://www.ebay.com/itm/285066554125. I used the 8 inch fan as it is a bit cheaper than the infinity and does 735 cfm more than enough https://www.ebay.com/itm/203764567923 spoofers are cheap if you do not want braiins there is a down side to doing this if the 8 inch fan fails the miner will overheat

If the fan fails its basically the same as when one (or more) of the small fans fail. The fw should stop hashing when it overheats, in Braiins OS controlled by the Dangerous value, which you can lower even more.

Thanks for that hint, that would be the easiest way to go I suppose. I've just been wondering why Braiins offers free software AND reduced mining fees if using this software. How does that work as a business model (ducking for cover  )?

I tested that and it works. When turning off all air flow to the miner, the chip temp goes up to 130C and it stops mining, then tries to restart a couple of times, then blinks the red LED and runs the fans on high without further mining. After power cycling, all is back to normal. When disconnecting a stock fan, it stops mining right away.

Well the unfortunate thing is that with factory fw it has to go very high and you cannot control it. It would be best if it didn't need to reach 130 to stop... The fan sense is a double edge sword. Sometimes a fan fails but its still registering RPM (can't turn on its own but is being pushed/pulled by the others), and you will notice higher temps, and sometimes lower RPM from that fan.

I installed BraiinsOS on SD card and I think the penny has dropped: It costs 2% to use Braiins pool when using other software; it costs 2.5% to use BraiinsOS and then the Braiins pool is free, means 2.5% fee in total, i.e. an extra 0.5% fee for Braiins compared to not using their software. The installation was very easy (for someone who has played around with miners for a few weeks) and now the S9J is running without noisy stock fans, just the Phresh fan sucking.

Actually the dev fee for S9 is still 2%, so if you want to see it that way, its 0%.