I noticed a good sized hole in an exterior wall that allows wires and things to go from my AC unit into my basement.

The problem is that the hole is a good deal larger than it needs to be and there is nothing sealing the hole, so I can see sunlight clearly through the hole.

What should I use to fill this hole in my wall preserving the important stuff going through the hole?

Click for full size

hole in the wooden exterior wall

  • Picture? What is going through the hole, how big is the hole?
    – auujay
    Commented Feb 3, 2012 at 22:17
  • Also, what material is used for the wall?
    – lqlarry
    Commented Feb 4, 2012 at 3:22

2 Answers 2


I would use Duct Seal

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I'm surprised whoever installed the AC unit didn't use it, it's used all the time by Electricians and HVAC technicians.

It does not harden; so unlike foam, it can be easily removed and replaced if you have to add/remove wiring/plumbing.

  • 2
    FYI: "Duct Seal" link is broken. Commented Apr 8, 2019 at 0:14

Usually all that is needed is a good outdoors silicon caulk. You can get a clear type or a paint-able white type.

  • 5
    "Do your best and caulk the rest!"
    – auujay
    Commented Feb 3, 2012 at 22:39
  • I like 'great stuff' for this sort of application. try the 'doors and windows' version.
    – Trout
    Commented Feb 3, 2012 at 22:58
  • 3
    Foam gap fillers (like Great Stuff) are very useful but are not the best way to seal exterior surfaces, because they break down faster when exposed to sunlight and/or water. An exterior-grade caulk is the way to go for a longer-lasting seal. Commented Feb 4, 2012 at 7:10
  • Painted Great Stuff last much longer.
    – Bryce
    Commented Sep 5, 2012 at 7:57

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