Here is one for you give me your thoughts Flue pipe and return air duct plenum.
Primitive heat recovery device?
Only you Mike! Only you?? I luv it.
flue pipe from where and to where???
Have any more photos of that? Just curious to see what else is going on.
No more pic’s one was enough just messing with your minds as it was mine when I first observed this from the far end of the attic it looked like it was inside of the duct plenum had to get a closer look. It was just resting on the top of the plenum had been abandoned from a previous wall furnace but was still exiting the roof.
This attic was full of insulation and very limited on head room could not see the ceiling joist had to balance on a pair of 2X12 on their side to get close enough to see what was actually going on. You big guys would not have made it:) 
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This was a death or more waiting to happen!! Any failure of the flue pipe here and CO gets distributed with heated air.
To quote Will Rogers: “Common sense isn’t all that common, is it?”
Please go back and read post #6:roll:
OOOHHHH!!! Speed reading skills failed me. Could it be age related?? And I thought a picture was worth a thousand words!!
That is why I posted the pic, looks can be deceiving. Perhaps you should slow and smell the roses.