I've decided to move an old floor air return to the baseboard. I am going to use two adjacent wall cavities and a ~30" grille.

Not sure what sort of duct I should use to run through the sill plate and mate to the grille, if any.

Is it okay to just cut holes in the sill plate and have no ducting at the grille, and then start ductwork below the subfloor? That will be easiest based on where studs and floor joists line up for this. A "standard" 10" wide stack header/boot won't fit without mods to go around the joists underneath.

Here's a picture of what I'm dealing with. PIcture

  • Can you annotate the picture to show where the original floor grate was located?
    – Michael Karas
    Jan 15, 2017 at 14:17
  • The original grate is where the metal one is in the pic, just at floor level. There was a box built where the old gigantic return was. The joists run top to bottom in the pic (also confusing due to box) Jan 15, 2017 at 14:23
  • 2
    A return air duct can be made from cavities within the building structure. However, the cavities have to be sealed such that air can only get in from conditioned space. If it's a supply duct, it must be made of an approved material.
    – Tester101
    Jan 15, 2017 at 14:25

1 Answer 1


Return ducts are commonly formed using cavities in framing and drywall. The vent opening is often nothing more than a sheet metal frame around which drywall is fit.

Use sheet metal, drywall, and existing framing to create your passage, and simply apply your vent grille where appropriate.


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