Duct Diameter ID/OD Convention?
Duct Diameter ID/OD Convention?
(OP)
We are having a discussion about duct diameters, and so I have a short question about Ductwork. Is there a generally accepted convention that understands that listing the size of a duct, automatically identifies the ID or OD of the duct? If so, which one? Is the convention the same for HVAC duct and Industrial duct?
I know that SMACNA has standards for duct, and that duct can be fabricated to any diameter and just about any gauge. And I know that drawings and specifications should be explicit, and that in many cases the difference is not critical. But we see many drawings, specs, and so forth that list a "round 16" duct". Didn't I say this was going to be a short question? Ooops.
Thanks
Harvey13
I know that SMACNA has standards for duct, and that duct can be fabricated to any diameter and just about any gauge. And I know that drawings and specifications should be explicit, and that in many cases the difference is not critical. But we see many drawings, specs, and so forth that list a "round 16" duct". Didn't I say this was going to be a short question? Ooops.
Thanks
Harvey13





RE: Duct Diameter ID/OD Convention?
The second part of your post isn't actually a question. What exactly are you asking?
RE: Duct Diameter ID/OD Convention?
The second half was just me running on too long, but also to make it clear that I know that ductwork can be just about any dimension. I would assume that industrial duct would be the same.
RE: Duct Diameter ID/OD Convention?
So if the duct is called out to have 1" liner, then the dimension provided is the free area, and the duct must be increased to accomodate the liner and free area requirement
knowledge is power
RE: Duct Diameter ID/OD Convention?
RE: Duct Diameter ID/OD Convention?
Sheet metal ducting off the shelf (KD) has a nominal diameter, which is usually ID at one end and OD at the other, so that the pieces can be fitted together. The tolerance is pretty generous on this stuff, so parts from one manufacturer may not always fit anothers.
As far as pipes with fitted angle rings, the rings are sized to allow for the thickness of metal of a nominal ID duct. Example 16" ID duct rolled from 16ga galv'd + od of of material = 16.116. Ring = 16.125 gives you just enough clearance to get the ring on. ( Sometimes)
B.E.
RE: Duct Diameter ID/OD Convention?
Arewin
RE: Duct Diameter ID/OD Convention?
I've had some interesting discussions regarding this with mechanical contractors upset at the level of detailing in our drawings.
From a consulting engineering standpoint, we are producing the engineered design. Our drawings are "diagrammatic in nature" and construction details have traditionally been left to the various subs to work out. I tell these guys that a mechanical contractor is a qualified license holder and sheet metal fabrication is a well documented trade, and they had better not be looking to my drawings to figure out how to construct this stuff.
I am interested to see how BIM continues to affect this traditional division of responsibilities. Personally, if I am expected to produce designs as well as coordinate shop drawing level ductwork drawings, I need a bigger fee.
Sorry for the slightly off-topic reply. This is something that gets under my skin from time to time.
www.ellisconsultingengineers.com
RE: Duct Diameter ID/OD Convention?
Contractors workshop drawings show metal sizes so the workshop guys fabricating the ductwork don't need to to think.
And as AnotherEllis mentions, BIM and Revit etc are making things interesting, particularly as Revit can only show metal dimensions.