Spiral duct diameter question for 40'x60' shop

[dreadman]

I have a shop (40'x60') in Austin TX, metal building, fully insulated. I am installing a split 5 ton Rheem HVAC system above the office. My plan is to run some spiral ducting right down the middle of the shop and cut out some registers on either side of the duct work to distribute the air.

Question is: What size/diameter spiral duct should I use? 12", 14", 16" ?

Here is a little sketch of my set-up and how I am planning to run the duct.

PS: It's about a 40' run of ducting.

Thanks

 

[fordguy64]

I'm not an hvac tec not do I pretend to know anything about it. But the average cfm per ton is 400 so you would need a duct big enough to flow 2000cfm. According to more google searching that puts you at about a 22" round duct. Over 40 feet I would think you would want to step down the duct size the further down you go. It has something to do with keeping pressure in the duct so that you get even air flow over the whole length.

Again I don't really know anything about hvac that's just what Google says..

 

[sixty4]

Did this in my 40x30 garage. 16" supply 18" return. My supply house said I could drop down a size or two but found a smoking deal on craigslist for the spiral duct. They have a chart called a ductulator as well. Click on picture for video.

 

[dreadman]

I'm not an hvac tec not do I pretend to know anything about it. But the average cfm per ton is 400 so you would need a duct big enough to flow 2000cfm. According to more google searching that puts you at about a 22" round duct. Over 40 feet I would think you would want to step down the duct size the further down you go. It has something to do with keeping pressure in the duct so that you get even air flow over the whole length.

Again I don't really know anything about hvac that's just what Google says..

Did this in my 40x30 garage. 16" supply 18" return. My supply house said I could drop down a size or two but found a smoking deal on craigslist for the spiral duct. They have a chart called a ductulator as well. Click on picture for video.

Thanks guys.
Stepping down the spiral duct a size or more over a certain distance makes sense, but I've seen both ways.
I'm tempted to start off with a 16" diameter pipe (10' long) and gradually drop down to 10" over 40 feet and install an end cap. Four 10' sections.

All the same size. (looks like 12" or 14")


Stepped down version.

 

[dreadman]

Anybody else have an idea, what size diameter duct I should use?
Thanks