I don’t have a photo looking down from the top, but I don’t remember seeing anything like it before. Anyone know what the purpose of this thing is?
It’s a shroud, fairly common around here.
Very typical on zero clearance fireplaces here.
Probably bring used to cover an extension that was added to the flue in an effort to create more draft or raise the height of the flue to meet required clearances on the adjacent roof of 3’ within ten feet. Just a guess.
Pretty common down here. There purpose is decorative, but probably help control back drafting too.