Sealing and insulating drywall within a range hood

Question

Our range hood looks like this:

I discovered a ton of freezing cold air coming from the top of the hood recently. I took a ladder, and it looked like this:

Cold air just pours through the opening.

Any suggestions for how to seal up the holes in the wall? Keep in mind this is not visible unless you are on a ladder, so something that is quicker/easier will win over something that looks pretty. Also, I'm not interested in pulling out the piping to wrap something around it, if at all possible, as that dramatically increases the level of complexity for me.

Additionally, is there any risk to sealing up the top of the range hood, or does it need to be left opened?

Answer 1

While I'd ordinarily reach for polyurethane spray foam, that may not be the best idea on a range exhaust duct that could conceivably have a grease fire inside it at some point in time.

Stuffing the hole/gap with rockwool would be relatively fast and easy, and fire-resistant (more than fiberglass, anyway.)

Slapping a scrap of drywall or cementboard over the open top area might further help, but you might need to dress up the edge of a sheet put there, as it would be visible from the floor.

But it slowly occurs to me that they do actually make a "fireblock" spray foam, and that would be just the ticket here, I think.