undersize vs underinsulate new flue liner

[centaurcoach]

"4 cu ft isn’t much insulation, that was one tight liner. We used 16 cu ft on our chimney when we insulated our liner."

Well it's a 5 1/2" liner inside a 7" terracotta x 30 feet. The question of undersizing the liner a bit to get the maximum insulation-- that's what started this whole thread. I was NOT going to bust out the terracotta; that much I knew. Like I said, I'm a happy little Lopi watcher.

 

[Battenkiller]

One more suggestion: instead of insulating the entire liner, maybe do just the top section, since that is where the creosote is. That could be done by stuffing some rock wool in from the top and tamping it down as far as possible (6, 8, 10 feet?) so it is tight between the tile and the liner. Then pouring in a small layer of cement/perlite to rest on top of the rock wool plug (thin enough that it could be broken out if needed). Then filling on top of that plug with loose perlite to the top.

Anyone have thoughts on that? Again, not likely to be technically code compliant.

My thoughts are that you get creosote up top because the gases started cooling below. If you're gonna insulate, insulate the whole thing IMO.