It would appear that my knowledge, reruns of This Old House, and YouTube have reached their limits. I am modifying a portion of our basement and I am stumped in finding any sort of details on how one would support and or brace 8’ of 3.5”x10” stack duct in a stud cavity. Once I’m out of the wall and into round pipe supported from the joists I’m good to go, but I’m stumped in how I should be supporting the rectangular duct within the stud cavity. Does al the weight just bear on the bottom register connection and the drywall just pins it in place?

flat piece of sheet metal 3 inches wide from stud to stud using pop rivets or sm screws two or three of the sheets would be plenty

I like simple and straightforward. Thanks for the help.

My suggestion would be duct tape.

You could even get fancy. Use one color for the vents and another for the returns.

Bending flat S-Cleat into your brace, screwing to the brace. The stack is often supported at the bottom rectangular elbow [plumbers would rightly call this fitting an 'elle'] and stabilized in its vertical location by more cleat.

It is not heavy but you do not want it shifting as it heats up, nor jumping around as you try to screw the register cover in place.

If I not mistaken, the part should have tabs that get nailed into the studs with roofing nails. I think they are bought that way.

I never installed them but have done a lot of demo and this is what I have noticed.

Oval stack head with wings at home depot is what is called.