HVAC DUCT GAUGE SELECTION

[immsk]

Hi guys,

I need some help here. I have the SMACNA HVAC duct construction standards book open in front of me. I am designing a 72" X 43" supply duct with a 3" in. wg static pressure and 29400 CFM. I would like to determine the appropriate sheet metal gauge to use for this application but I am not really sure what to do Table 1-6 in the booklet does not have anything beyond circular diameter of 24". Any guidance would be appreciated.

 

[Drazen]

could you look a little more into tables?

i don't have whole smacna book, but i do have table excerpts, and in some of my tables 28" is smallest dimension, while largest one is " over 96" "

be sure to make difference between true circular ducts and equivalent diameters of rectangular ducts, as the tables are not interchangeable, stiffness and construction are different.

 

[DrRTU]

Without seeing the application, It sounds like your duct is oversized for that flow. This is what we would build - 56.25” length with TDC both ends, gauge = 22 all sides, small pits, seal all seams, 1.5x1.5x1.5 intermediate reinforcing at mid span of the 56.25” only on 72” sides. Two (2) condu-loc tie rods 1” in from both ends in the center of the 72 span. Hang at 9’-6” intervals wrod/angle or gripple. I believe this meets the latest designs and should be the best value.

 

[MechEngNCPE]

72x43? I would go with at 60x36 if you can. That is only .1"/100ft drop at that flow and 2250 fpm. And why the 43? When the next guy goes to measure the duct when it's insulated he's going to call it a 42 or 44, so why not stick to regular sizes.