I'm in the process of having to clean up after some sloppy installation work by my builder's HVAC subcontractor.
Basically, they left gaps between the supply and return boots and the surrounding construction, which is allowing some crawlspace/attic air to leak into the returns and supply air to leak into the crawlspace/attic.
Downstairs, all the supplies are in the floor, so I had some gaps open to the crawlspace. I sealed between the boot and the wood or tile with metal tape which would stick to both surfaces pretty well and seemed to work OK.
Upstairs, though, all the openings are in the ceiling drywall, which means I'm sucking some air into the returns from the attic and/or blowing some supply air up there also.
Tape isn't going to stick to the drywall too well. What should I use here? I was hoping there would be some sort of expandable-foam insulation type product that woudn't be too hard, but I'll use whatever you guys recommend.