Proper Termination of Duct Stack Head to Wall?

Steamback

My neighbor has an issue where his HVAC contractor left huge gaps between the duct stack heads and the walls. I told him I'd help but know little about duct installation.

I imagined (but can't find) a type of sheet metal fitting meant to finish these terminations? Like a flanged insert that overlaps the wall and slides into the stack head, also providing a solid material for the register cover screws to anchor to (other than drywall or tile)?

Anyway, I'm in need of professional advice on how to finish these stack head to wall connections. Hopefully it is a common fitting or assembly, rather than caulk/spray foam/adhesive tape type fix. Thanks in advance.

mattmia2

You could bend a flange to put around it, maybe use some s cleats on the deeper ones. Can seal it with mastic. if the part you can see looks like that the part you can't likely leaks like a sieve.

Those probably have a tab on each side that is nailed to the framing.

Steamback

Thanks mattmla2. I did leave out that last year I sealed with mastic most of the plenum and branches in basement. It was all new work the HVAC contractor never finished. It didn't even occur to me that the upstairs register areas were like that. Air quality is the main driver here, so he wants these stack heads sealed too. But yes, any duct joints in the wall probably don't have mastic, unfortunately.

EBEBRATT-Ed

Have a sheet metal shop make you some 1" x 1" angle made out of sheet metal at least 24 gauge or heavier. Screw it to the duct opening on the inside or outside to screw the register to it. or use pop rivets