I'm trying to build a well insulated house, trying to avoid thermal bridging etc.
Just realised that the chimney stack sticking out of the roof is a big heat sink. I've got a big thermal store at the bottom of the flue, a thick wall of concrete blocks, heated by a wood burning stove, but it's going to leak its heat to outside via the chimney masonry.
Would there be reduced heat loss if I fit a stainless steel insulated flue from first floor level through the roof?
Does anyone have any other ideas?

Hello Guest,
But what would I do with the foamglass?

Good proprietory ceramic flues are usually good insulators eg pumice