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Ok, it’s been awhile since I posted, but I finally got the 1200 CFM fan installed into my small space 5’x5’x8’ converted wine room.  As you can see from my pictures, I’ve hung the fan from 2x4 studs. The fan utilizes 8’ of 10 inch duct to expel the hot air out the side of my house.  I’ve also removed the old wine cooling unit and you can see the resulting open square left in the wall.  I will bring fresh air in through that opening.  I hooking up a generic 2.5 foot house fan to that black duct you see coming from the open square.  However, that’s not working at all.  When I shut the door, my miners heat up to 42 C real quick.  Do you guys think I need to buy another 1200 (or higher) CFM fan and push fresh air through that square?  Right now, I have 5 Avalon 741s running.  I’m not sure how to expel all this heat effectively?

https://imgur.com/gallery/3jUrs

Thanks for your help,
Steve

Judging by the picture you posted, you would need another fan to help push in air from the outside. You might wanna put it on the adjacent wall, that way the air has a chance to circulate thus dispersing some of the heat. One fan will not be able to cool that tiny room.

Avalon 741 has a 250cfm fan. Having 5 of them gives you a total of 1250cfm. Plus the heat load from the power supply.. i suppose you have 1600W PSU running them. Your 1200CFM fan is not enough to expel all the hot air coming from your miners and power supply. Also, those flexible aluminum duct has high friction loss. Your 10" flex duct gives around 3050FPM air velocity at 1200cfm of air.

Either change your fan and make it around 1500-2000 cfm, or add another one. Then change your flex duct. It is quite small for your air volume. If the other side of that square opening where your flex duct is already outside the house, just make a screen with filter for better airflow. Window opening should be atleast 1.5 times the area of your exhaust fan duct area, BUT it should be below your miner or else there will be "short circuit" in your air flow. Fresh air will just exhaust out right away by your fan.

You have two choices the way I see it. If you don't relocate your window opening below, put a duct to your exhaust fan and extend it beside the fans of your miners so it can easily suck up the hot air (change your duct size). Or, leave your exhaust fan up there and relocate your window below, put louver/grille/screen and filter. Whichever makes it easier for you.

Thanks for the help.  My original design was to hook the 5 miners up with ducts to a "hot air receptacle" and then suck the hot air out of the receptacle with duct work to the inline fan.  I may try to go that route, and also add a better/more powerful fan.  I think my 1200 cfm could probably act as the fan that pushes fresh air in, but I'll need a bigger fan to draw out the hot air.  Anyway, thanks.

You want the path: (fresh air) -> (machines) -> (outside) to be as wide and have as few turns as possible, while still being fairly direct.
Is dumping the heat into a "receptacle" and then bringing it out going to be a wide open path, or will it just let the heat pool up?
Why not let the entire room be a "duct"?
Is the flex duct running between studs?  If so can you just pan the studs so the channel forms a natural "duct"?
What's above this room?  Attic? Perhaps you could open the entire ceiling, extend wall up and over, and put gable fans on side of house.

What do you mean by "pan the studs"?  Yes, flex duct is running from the top of the 1200 cfm fan between the studs and outside the house.  Its about 8 feet w/ 1 turn at the top.  I cannot open the ceiling as the kitchen is above that room.

Also, the square hole left over from the wine cooling unit dumps to a closet in a guest bedroom.  So, the fresh air I will be bringing in is not from the outside.  Its room temperature air from the guest room.

Not ideal.  This small space has been a challenge.

You could combine your current idea with your first plan. By using flex ducting from your miners up to the intake for your exhaust fan by doing this you will be using your miners fans to assist the exhaust fan to remove the heat, I would use slightly oversized flex ducting to reduce friction. It would require you to maneuver your miners a bit to avoid having any extra bends in the ducting, and this way your fan should be able to exhaust all heat, as it will almost be working like an inline fan and almost all of its intake will be direct from the miners.

Or you can fab up a receiver at the intake of your fan and run rigid ducting from the miners directly up to it. This closed system would work as the rigid ducting won't collapse from the fans suction, and all of the air it pushes out will be direct from the miners themselves.

You could do this with a few sheets of duct material some tape. The bitch would be cutting in the holes for the Miner exhaust ducts to join in. Here's an idea of the duct material to build the receiver box at the fan intake.

https://www.homedepot.ca/en/home/p.8x16x60-inch-main-duct-28ga.1000407246.html

he is spot on    that is not a good duct this is better

https://www.homedepot.com/p/Speedi-Products-16-in-x-12-ft-Insulated-Flexible-Duct-with-Metalized-Jacket-R8-FD-12R8-16/203393287?keyword=16+in+flex+duct

this is a better fan

https://www.homedepot.com/p/Master-Flow-1600-CFM-Power-Gable-Mount-Attic-Fan-EGV6/205924917

  if you  replace  what you have with above and then  use what you have to pull air in it should work.

or look at photo

https://i.imgur.com/UFThd49.png

I think he was saying that wall has his guest room closet on the other side if it.