Old house. Part basement, part crawlspace. There are heat and cold air boxes in the floor over the crawlspace. The (round) ducts for these pass through (very) rough openings knocked through the (limestone?) foundation wall of the basement.
Right now, I have insulation stuffed around the ducts, to close the openings. (The crawlspace is cold, unconditioned.)
There's probably a better way to do that? I'm thinking to block it in as best I can with masonry, and fill the rest with ...?
Thanks