5. Open fire chimneys & closed stove chimneys.

The virtuous thing about open fires (A.) is that they draw a large volume of air upwards into the chimney. This helps to distribute the heat evenly as well as drying up any damp patches. Click here to see what a chimney looks like in cross-section when serving an open fire.
XXA chimney serving a closed stove (B.) behaves in a completely different way. Only a tiny volume of air is drawn in – not enough to distribute the heat upwards, and not enough to dilute the tars, creostes and water vapour contained in the smoke.
XXSo the stove chimney often runs at a very high temperature indeed just above the stove, but a little further up it may cool rapidly to the point where the 'nasties' have all the time in the world to condense out.
XXThe result can be both a fire hazard and actual degradation of surrounding masonry caused by the acidic, black goo that may pentrate outwards wherever the mortar is porous. Even a brand-new tiled liner may suffer if there are flaws in the joints, or pin-holes – or, as has happened on more than one occasion, the tiled liners have been installed upside down!
XXClick here to see what an unlined chimney serving a closed stove may look like.