I have a 1956 house near Los Angeles.

We replaced the whole HVAC system 6 years ago, including ductwork. The contractor removed all the old ducts, but we still have all the old wall registers. They covered up the openings behind the registers with what looks like Foil-Grip rolled mastic sealant (silver tape).

I want to figure out a more permanent solution and I’m starting with the old air intake (26”x17” opening) since I have other repairs to do on that wall. I peeled back the tape and it looks like it is just open to the raised foundation below, so I’m guessing it’s better to do more than just patch the interior wall. Insulation?

Our interior walls are rock lathe plaster - about 1/2” of plaster applied on top of something similar to drywall, if that makes a difference.

Anyway, looking for suggestions on something I can DIY, or what I should ask a contractor to do. The HVAC guy who installed our new system has since retired.

  • Pictures of what you're seeing would help. Are you concerned only about the walls (interior or exterior) or are you concerned about floor penetrations too? Also, if you'll take the tour you'll note that this is a Question & Answer forum and the only question you've actually asked is "Insulation?" which isn't much to go on. "Suggestions..." is pretty broad, so if you'll specify what you're concerned about, we can offer specific pointers to address those things, just asking a very open-ended question isn't a good fit for here.
    – FreeMan
    Commented Sep 8, 2023 at 18:40


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