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Community and Q&A

Air sealing electrical boxes

Joe Norm | Posted in General Questions on

I am finishing up my wiring and am wondering if anyone has had good luck with the cardboard box product that you fill with foam around the electrical boxes? There was an article about them here awhile back.

Does anyone have other suggestions for this task? I did not use any boxes with seals, just standard, cheap blue plastic.
I also have a limited number of round light boxes in the ceiling I should treat as well

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  1. Expert Member
    Zephyr7 | | #1

    My favorite way to seal them is with red silicone caulk — the “high temperature” stuff, not the intumescent stuff. Smear some in all the holes in the box, preferably from the outside. You can used canned foam on the outside if you’re careful, but you don’t want to let the foam expand into the box.

    If you can get the white fiberglass “hard boxes” those are much easier to seal than the blue plastic boxes. The white fiberglass boxes have no holes or gaps, so you only have to air seal around the cables in whichever knockouts you pop out for wiring. The rest of the box is one solid piece.


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