I've got a couple of old furnace ducts near the ceiling in a couple of
rooms in the house. I've since had new ducts put in the floor, and
these upper ducts were simply closed off (but not sealed).
It's time to repaint, and I'd like to close up the upper ducts
permanently and plaster over the openings. I figure I'll have to seal
them off some way; otherwise I'll end up pumping hot air into the
walls and eventually into the attic. That would be a bad thing, as I
live in Canada. Probably a bad thing anywhere...
So, my question is, what is the best way to seal up these ducts? Is
there something I can spray into them to block the air flow? There is
really nowhere that I can apply metal tape.
I guess a picture would be better, but not knowing how to add one,
I'll try to describe what they look like.
The duct opens to 12"x6" flush with the wall face and is 4" deep.
Looking up and in, the duct seems to extend up about an inch or two,
where it joins with a 12"x3" duct that feeds down from the attic.
1) One option is to try and rip the larger duct completely out of the
wall, without leaving a huge mess behind. Then I'll have to cap the
12x3, but it will be tough trying to work in a cramped area.
2) The other option, as I see it, is to hammer back the edges of the
duct that are flush with the wall, and then fit a small square of
wallboard over the old opening using the hammered edges as a back
support. I'll then plaster and tape the sides.
I'm leaning towards option #2, since it has the potential to be less
messy. But either way I'll need to seal up the duct.
Well, that is basically what I thought you said in your original post --
put a piece of wallboard over the opening and plaster/tape it and were
wondering if you really needed to have a sealed end for the ducts
themselves independent of the wallboard/plaster.
If it is "real" plaster instead of just wallboard so it is more of an
issue in making an opening, you could simply take a sawzall and cut them
back. Or, as you say, just bend the tin edges back so they don't reach
the surface. You could if there is some real problem in doing that
simply screw a backer piece on the inside of the duct itself as the
support for the patch and set it inside the duct and tape over the edge
as long as the actual duct itself is behind the surface. It doesn't
need anything other than some way to hold a patch in place to finish over.
If it's just wallboard/sheetrock, cut it back to the midpoint of the
joists and use them for the mounting points.
Are you sure you want to seal them off? If you use central AC, it's better
for it to come in from the ceiling than the floor. Since you're in Canada,
I doubt this is a concern for you, but I thought I'd mention it.
Can you get into the attic and disconnect the duct from there, and then put
an endcap on it? I imagine the closer you can get to the furnace, the less
unwanted duct you'll be paying to heat. Especially if it's going through an
If nothing else, you can just shove some insulation batt into the opening.
That should stop that section of the wall from being over-heated or whatever
it is you're worried about. You could also tape some plastic on the inside
of the duct to stop all airflow (but note that I'm not an HVAC person and
don't really know what the long-term consequences of this is).
Good luck with it all :)
I think the first thing is to find out for sure what that duct is doing
(return air maybe?)
If it truly dead, then I would want to remove the necessary parts and
patch the wall to totally erase any evidence of them.
What, you mean the entire duct? That would require removing a bunch of
If you want to eliminate or re-locate a vent, I would suggest just cutting
some sheet Al to fit over then opening. Drive some sheet metal screws to
hold it in place and "seal" it with METAL duct tape.
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