10. An exposed, chilled chimney can reverse its draught.

The residual heat in a house will continue to produce a weak, convective airflow even when the heat is low or has been turned off. As warm air rises in the building and seeps out through the upper levels, cold air is drawn into the building at ankle level to replace it.
XXUnder these conditions, the air in an exposed chimney may be chilled to such a low level that it sinks down and dribbles in a 'backflow' out through the stove and into the house, carrying with it the unpleasant smells of tars and creosotes.
XXAttempts to light the fire when the chimney is in this condition can be frustrating. Smoke and flame will continue to dribble out into the room until there is sufficient heat in the vertical column to generate a strong, positive updraught. In the mean time, you can spend much time on your knees blowing into the embers while your eyes smart.
XXAll of which is a further strong case for designing every chimney in such a way that it is kept well within the main body of the house and remains warm and dry at all times!