8. Chimney constructional materials – the case for high xxinsulation & low mass.

Temperature plays such a major part in a chimney's performance that it's worth giving special consideration to the thermal properties of the materials used in its construction.
XXOld-fashioned brick chimneys date back to an era when architects & builders were more or less forced to work with the raw materials already on-site. And a well-built masonry chimney had a lot going for it when open fires were the norm, because as we have seen, open fires are 'kind' to chimneys. By causing a large volume of warm, dry air to to percolate upwards in a continuous stream, they keep everything in good order.
XXBy contrast, some modern, high efficiency stoves leak so little heat to the chimney that it runs almost permanently cold – with consequences that can be dire. Draught performance plummets while precipitation levels soar. It doesn't do to try and make a stove installation too efficient. As well as the heat needed to create adequate draught we need a minimum surface temperature of at least 50°C. throughout an installation just to stop it from precipitating undesirable quantities of flammable goo.
XXSo modern woodburners are best served by well-insulated low-mass flues. This was demonstrated earlier when we noted all the good things that happen after a bricks & mortar chimney is fitted with a low-mass liner properly back-filled with insulating material.
XXHowever, anyone about to build a new chimney for a wood stove would be well advised to look at the very real advantages to be had by using a modern stainless-steel sectional chimney. These have all the things we look for 'designed in' including low-mass high insulation properties and ease of maintainance.