Never seen this done before - stripped the outside off of flue

This furnace flue used to be double walled.
Not so much now.
Whoever installed it had a clearance issue with some ductwork, so they just stripped the outside wall off.
But why leave the spacers?
Just when I thought I’d seen everything.

It was most likely the asbestos insulation that surrounded the pipes. That was the reason it was removed.

Those are added radiators

They were quite popular a couple of decades ago.


The first thing I thought was that they must be some kind of heatsink. But then I couldn’t figure out what the advantage would be.
Were they trying to rust out the flue by making the exhaust gas condense? Because other than heating the immediate area I don’t see any other purpose. And that’d only be if they worked well, which they didn’t appear to do…
The old guy that was with me said that had seen double wall pipe stripped down before, and I looked at some pictures online where the spacers looked very similar to these, and the clearance did suck, so I figured he was right.
Dude was 85yrs old and still working as a PE. Was a master electrician and had been working as an electrician for 75yrs. That’s right, since he was 10.
His dad died when he was 8.
Seemed like he knew what he was talking about.
Either way, I’ve never seen them before.

Really Andy they are add ons with the intention of saving wasted heat going up the Flue and as You noted not very effective…

Well I’ll be…
Just goes to show that even after all these years, there’s still stuff I haven’t seen.