7. Beware the long, slow burning cycle.

However good your chimney might be, you can do a great deal of damage to it simply by running in incorrectly.
XXA common fault is the 'slow burn' syndrome. Loading a stove with wood or peat and turning it down to its lowest setting for hours at a stretch (particularly overnight) is never good practice. Why? Because in the first place you need a minimum temperature in the firebox to burn the fuel cleanly. Go below that temperature and you get a continuous pall of dense, humid smoke loaded with unburned tars and creosotes.
XXSecondly, since the chimney is no longer being heated adequately by the stove, it cools down. Draught then becomes sluggish and at the same time high levels of precipitation develop.
XXAn identical problem tends to arise when a stove is too big for the job it's doing. A natural response is to under-run it to keep the room from over-heating – but again with the risk of storing up serious chimney problems.
XXThe solution to all this is to aim for an installation that needs to be run brightly for reasonable periods of time. And if you fall into the trap of under-running your stove, at least get into the habit of burning it up brightly at regular intervals. This will help to dry up moist patches and blow out the 'cobwebs.'

Click here to see what an unlined chimney can look like in cross-section when when it is serving a closed stove.