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I relocated a small house to a new foundation but all the HVAC flexduct was destroyed by the move. I have the original Goodman 2.5 ton unit, circa 2003, and the 20'x20"x8" sheet metal distribution plenum from which all the 6" branches run to the registers. The plenum (if that's the right word) has (8) 6" cutouts for the branch ducts, so if I install it in its original location, it should be a fairly simple matter to route the ductwork to the registers. But, here's what I don't know:

  1. How to reattach the 6" duct connectors to the plenum (the connectors are a piece of 6" stovepipe with tabs on the end)
  2. What kind of flexduct to buy - Big Orange has foil-covered stuff, but should I be sourcing at an HVAC supplier
  3. House is about 900 sq.ft. living space - should I insulate before hanging ductwork? I have looked for videos on this kind of job, but found nothing yet that helps.

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You'll need to straighten the tabs of the connectors, reinsert the connectors back into the plenum and bend the tabs back up against the inside of the plenum. Use a duct seal, AC rated mastic, to seal the connector to the plenum.

The foil covered stuff is insulated and is what you should use. The black inside tube gets routed over the connector and held in place with AC foil tape. The insulation and foil layers get pulled over the black tubing and get held in place with tie strips.

Insulating the attic before installing the ducts is a good idea. It will make the process easier if you don't have to maneuver around the ducts.

Just a side note. You mentioned sourcing the duct from a HVAC supplier. The people that work in these supply stores know tricks of the trade you'd never think of and they'll have everything you'll need to do the job and will take the time to explain all you need to know.

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  • This is very helpful, and makes sense - Thank you. One problem: how does one bend the tabs back up against the inside of the plenum when it is in two 10 ft. sections with the cutouts unreachable from the end? Is there some sort of clever tool that fits through the connector, expands to flatten the tabs, and then collapses so it can be drawn through the connector? BTW, its a crawl space, not an attic, but the advice about insulation is relevant.
    – AKG
    Nov 13, 2021 at 21:37
  • @AKG Have never seen a clever tool for this. You might have to cut the old connector off the duct, install a short one into the plenum and connect the duct to it. I'm surprised there's no break between the connector and duct.
    – JACK
    Nov 13, 2021 at 22:18
  • After thinking about it, I think the clever tool is a hand with a block of wood, reaching through the connector and mashing the tabs up. Should the connector be secured with sheet metal screws? Or just tape?
    – AKG
    Nov 14, 2021 at 0:14
  • @AKG Was there a break between the connector and the 10' section? or did you cut the duct?
    – JACK
    Nov 14, 2021 at 0:35
  • Connector with tabs to plenum, use AC mastic. Connector to metal duct, use screws and AC foil tape
    – JACK
    Nov 14, 2021 at 0:38

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