I was preparing to install a hood vent this weekend and found myself with a bit of an issue...

Here's what it looks like:


The larger hole in the middle is the center point over my cooktop and the red line is a 2x4 ceiling joist going over the top. The 4 smaller holes are where the mounting plate for the hood attaches (they look off but that's the angle of the picture).

I need to put a 6" circle in the ceiling to run the ducting through and that's pretty impossible here. I'm assuming I can't cut the joist, or maybe I can if I hire a carpenter to somehow shore it up. I think I could remove some metal from the mounting bracket and fit it though. The bracket looks like this:

Mounting Bracket

If I basically cut out one side I can probably get a flexible 6" duct through the offset hole. However I'm worried that this could impact the strength of the bracket, and also that flexible ducting might collect grease in the ridges of the tube.

Any thoughts or other suggestions on how I could tackle this and what the best option may be?

  • Cutting out so much metal not only would weaken the bracket, but reduce its efficacy as a fire-stop. And cutting and reinforcing a joist is not trivial. Can't you reposition the hood? Buying a different hood would still be cheaper and safer than cutting the joist, I think. Commented May 10, 2021 at 1:30
  • 1
    I can move the hood over 3" but then it's going to be off center from the cook top which is going to look strange and it will also end up hanging over the edge of the counter and get into the walkway right next to this. I don't think a different hood would matter, they all require ducting right up the middle.
    – Chad
    Commented May 10, 2021 at 1:35
  • How far is the location form a wall? A wall-mount might work better, here. It also might be possible to build a metal air plenum between the hood and outlet, allowing for offset. It would need some thought to sealing, to allowing sufficient airflow, and to accessibility for cleaning. Commented May 10, 2021 at 1:41
  • It's over an island, nowhere near a wall.
    – Chad
    Commented May 10, 2021 at 1:56
  • I assume the hood is screwed to this bracket. It looks like there's threaded inserts but I can't tell from the photo whether the hood is screwed to the bracket at the corners or in the middle. If it's screwed at the corners then you should be fine with cutting it. If it's screwed in the middle then I wouldn't cut it. I can't see that bracket being a fire-stop with that big square opening. If you're concerned you can buy a piece of sheet steel and patch it. I would also run some 2x4's perpendicular between the joists and screw the bracket into them. Commented May 10, 2021 at 3:28

2 Answers 2


I would cut your "Top Support Plate" (as it's called in the picture you linked in one of your comments), as you suggest in the picture of your question.

Attach a metal 6in 90 to drop down (as I suppose you were going to), and then 6in ducting down and attached to the vent unit, all inside the shrouded box.

There seems to be enough distance down to allow a minor slant to this portion of the vent, form the off centre exit point at the top plate, down to the fan unit.

And attach the plate to the joist for extra strength.


I wouldn't be too concerned cutting the mounting plate since the fasteners are in the corner. But there is another option if the parts are available where you are.

And that is to buy a couple of round to square connectors and some flat square pipe (well, it's oblong or rectangular really).

Flat oblong piping is often used on top of cabinets for it's lower profile, so it's not seen from the floor.

Cut the round ally duct under the ceiling, convert to square pipe and then once you're past the joist, convert back again.

  • I considered goign with like a 3" x 6" oval profile duct through there, my concern would be that it would have less area than a 6" round duct and I'm not sure if that would put excess strain on the fan or cause excessive noise.
    – Chad
    Commented May 13, 2021 at 14:24

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