Heat dispersing flanges on woodburner flue?

Hi all,

One of our woodburners has become much less efficient since we had the chimney lined.
(irritating as it had worked really well before we took the advice of the sweep and had it lined)

Because of fears of timber and pipes in the chimney, it has 2 lengths of double lined flue running right down to the back of the burner itself, so a lot more of the heat is going up the chimney, and less into the room itself. It's also a lot more difficult to control, running right at the edge of all vents closed to keep it under control. The stove fitter didn't seem able to think about any of this when he put the flue in. Ho humm.
I'll look for a fitter to sort this out, and it seems likely that the top section of double lining could be raised up to protect both the suspected timber and pipes, so the lower section could be replaced with single skin.

The draw on the stove was just fine with just the chimney, no lining, so it seems clear that we could keep more of the heat in the room without problems.

What do you think of the idea of fixing heat dispersing flanges (heatsinks, maybe like you get on the top half of a ecofan) EDIT or convection tubes, on either side of the single skin flue between the top of the burner and the bottom of the register plate? Like the pic below except less crap and to scale!

EDIT Here's another reference point for my idea:

 

I don't know if they meet regulations, if you're fussed by that, by have you look at flue dampers?

 

Thanks - a useful reminder and appreciated - something to talk to a fitter about