The pictures attached show a heating supply duct (or possibly a cold air return duct) in the attic of a circa 1955 home (bungalo) in Toronto Ontario. It was located just inside the attic access hatch. Pictures a little blurry, sorry.
I ran the furnace to see if it was either supplying or returning air and neither case was true (disconnected and / or sealed over the years I guess). I recommended sealing the opening in case a critter found its way into the attic and crawled into the open duct where it there got stuck and met its maker…
Has anyone ever seen this before? I can’t see it being a supply duct for an attic air conditioner… we don’t have many of those up here - or at least none that I have seen.
The house has its own A/C external compressor unit (over 20 years old).