View Full Version : Playing with SMACNA standards

12-07-2009, 10:14 AM
Let's look at a 30X16 duct, 5' long, slip and drive. Now, SMACNA says that at 1" negative static, this duct must be 26ga and have a "D" class reinforcement which is a 20ga T-11 standing S. For whatever reason, I want to use a 22ga T-11 standing S. Can't I just increase the gauge of the duct to make up the difference? How do I know how much SMACNA needs it increased to make up the difference? I just want to know that my butt is covered.

12-07-2009, 07:14 PM
It's been a long time since I've done duct but the rule of thunb was over 12" went to 24ga. Somewhere around 30" 22ga. We also used "Barlocks" (standing "S's") and drives. Peace dupree

12-07-2009, 09:31 PM
I'll look it up tomorrow and get back to you. I used to work up the SMACNA charts for my employer and a few of my ideas made it to the standards books of SMACNA. My employer was on a committee.

You should be able to use tie rods rather than heaver gauge and meet the standards. 1/2" conduit behind the joint comes to mind.

Better answer tomorrow to cover you, it's going on midnight here now.

12-15-2009, 07:37 AM
Another idea is to call up and ask your local SMACNA rep. They are usually pretty willing to help out with information when my company calls them up.