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seal around heating ducts to prevent pests

Our house is built into the side of a hill. The lower level consists of two areas: a crawlspace and an unfinished basement area. A floor-to-joist concrete block wall separates the two. Heating ducts run from the “crawlspace,” through the joist spaces over the block wall, and into the unfinished basement area. We want to make a playroom in the basement area, but first must seal the open space between the joists around the heating duct (over the block wall) so that no pests can get into the space between the house subfloor (above) and the ceiling we will put in for the playroom. The duct lies in the space between the two joists next to an outside wall, and it is difficult to see, or even feel, into the top corner over the duct. A couple of times, field mice have come into the basement via the heating ducts. I stuffed rags around the duct from block wall to subfloor and joist-to-joist – which solved the mouse-entry problem. But before installing a ceiling in the playroom, we need a more permanent seal, hopefully without removing the duct. I have tried Great-stuff foam in another area, but because the area around this duct is open in two directions, I can’t be assured that it will expand to cover where I can’t see or feel. Can anyone suggest some type of material that we can “stuff” around the duct (from subfloor to ceiling and joist to joist with the duct running through the middle) with confidence that it will fill the void and not permit mice to chew their way through? And keep in mind that I cannot see or feel into a top corner over the duct to assure myself that no holes exist in the “packing.”

Re: seal around heating ducts to prevent pests

Try a galvy sheet cut to the joist bay dimension plus 1/2-1 inch as a nail flange.
Cut out the duct diameter then cut that sheet in half.
Slide one half from the top over the duct then slide the bottom half and tack the sheet to the joist.

Re: seal around heating ducts to prevent pests

Thanks - good idea.

Re: seal around heating ducts to prevent pests

Can you get a cell phone or digital camera in there to get a look?

Adding a section of hose to the foam in a can also works for hard to reach places. You can fill it bit by bit, taking a picture as you go. The foam doubles in size so it may take a while to get the hole properly filled.

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