I’m installing a wood stove insert into my fireplace, with a chimney liner. The top of the chimney is capped off so “in theory” there is a cavity of dead air space in the chimney. In practice there will still be some air movement there, and also more importantly heat loss. I was thinking why not pack the chimney with mineral wool? Is that discussed on the site? Are there any designs/thoughts for how to hold the mineral wool in place for a sort of “standard” chimney?