Connecting 10"x3.25" rectangular duct in wall cavity

Question

I'm trying to run a few heat ducts in my basement with 10"x3.25" rectangular duct in the 2x4 framed walls to bring the heat down to the floor. I'm using S cleats on the long edges and drive cleats on the short edges. The duct itself is 3-3/8" thick but the whole assembly is coming in at about 3-3/4" thick at the joints (specifically where the ends of the drive cleat overlap the s cleat) when they need to fit in a 3-1/2" wall cavity.

• is the S-cleat and drive-cleat approach still the correct one in this case?
• Is there a special technique for keeping these connections compact or am I just doing sloppy work?
• If it's just me, what should I do differently to get these joints tighter?
• should I shorten the S cleat so the drive cleat doesn't overlap it?
• should I trim the end of the drive class so it's only a single layer overlapping?

Answer 1

That duct material is manufactured for S and drive cleats the way you've described but you don't have to use it that way.

If you un-fold the drive cleat part, or simply cut the duct all the way around to remove it, then you can use S cleat on all four sides. Slap a bit of quality (foil) duct tape over the corners to close up any gaps.

Now that I've written all that -- I guess you could just as well cut the drive cleats short so that they don't fold around the duct. Drive a sheet metal screw in through the cleat to prevent it sliding, and tape the corners if needed to stop leaks.