Question for the AC guys

[kmitchl]

Installing AC unit in my shop. Floor area is 40’ x 40’. Plan is the run one supply duct 30’ down one side with multiple discharge registers. Is there a better way than fabricating a supply duct from duct board? It’s five tons so should run about 2000 cfm. Any creative ideas?

[Smokeater]

Ductboard plenum would be fine, then go get the metal duct and insulate it. Less friction loss inside and will last longer. One of the tbh A/C guys can tell you what size. I'm a has-been!

[LonestarGent]

Double wall spiral iif you want it to look good

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[kmitchl]

Double wall spiral iif you want it to look good

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I’ve see that in commercial buildings. Any idea of the cost? I’m looking at around $400 for duct board.

[bowhntrmatt]

I’ve see that in commercial buildings. Any idea of the cost? I’m looking at around $400 for duct board.

I’m not sure but it’s definitely the way to go. Duct board the whole way will look like crap after a few years of exposure. Spiral pipe for sure.

[elliscountyhog]

Spend the extra and go with Spiral duct. Can do paint grip with black or galvanized and then saddle boots on the side. Looks good. Plus the labor/time is easier then ductboard IMO

[double bogey]

Ductboard is crap.

[kmitchl]

Can someone point me to where I can buy the spiral duct. Do the supply houses stock it? I’m not google impaired but not a HVAC guy either.

[LonestarGent]

Can someone point me to where I can buy the spiral duct. Do the supply houses stock it? I’m not google impaired but not a HVAC guy either.

M&M Manufacturing is where I get all mine but idk if they sale to the general public

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[LonestarGent]

Also if it's exposed you won't need double wall, just single wall.

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[kmitchl]

M&M Manufacturing is where I get all mine but idk if they sale to the general public

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I will give them a call. I have a company. That usually helps. If they won’t I’ll see if they have a distributor. Does this stuff come in 10’ lengths that get joined in the field?

[kmitchl]

Also if it's exposed you won't need double wall, just single wall.

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So if all the duct work is within the conditioned space the insulation is not required? I had wondered about that.

[elliscountyhog]

Also if it's exposed you won't need double wall, just single wall.

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Inside a shop where the door may open and close quite a bit or system off for periods of time I would go double wall. But for sure if going to stay on and maintain temperature like a house or regular used space then single wall is fine.


IF you don't care what it looks like go spiral duct work with or without insulation depending on conditions as I stated above. Still way better then duct board but not as nice or good looking as spiral.

[Uncle Saggy]

Once you decide on what duct to use, have someone size it to reduce in size after takeoffs....this will maintain static.
Me, I’d go square/rectangular trunk

[kmitchl]

Inside a shop where the door may open and close quite a bit or system off for periods of time I would go double wall. But for sure if going to stay on and maintain temperature like a house or regular used space then single wall is fine.

I have a machine shop in the building. My goal in doing the HVAC is to run the shop at around 80 degrees in summer and 65 in winter but keep the humidity at around 50% so my tools don’t rust. I have one insulated 12 x 14 roll up door that is seldom opened. The walk door is open long enough to get in or out. So I’m thinking bare metal will work.