11. The Importance of Height.

Height plays an important part in the performance of a chimney. A minimum volume of warm, buoyant flue-gas needs to be present inside any chimney to generate adequate draught. In some case things are so finely balanced that increasing height by a metre or less can make a big difference to operating comfort. This won't necessarily work though if the extra metre you add runs cold owing to extreme exposure to the weather.
XXChimney height is particularly critical when a large, central-heating cooker with ovens is being installed (A.) For much of the time these appliances are in 'tick-over' mode and lose only a tiny dribble of heat to the chimney. Yet they demand a vigorous draught to pull on the fire so that it burns efficiently and so that the heat is pulled around the lengthy channels serving the ovens and hobs. To get the optimum performance from this type of appliance, a warm-running chimney of adequate height and diameter is essential. As an example, the Rayburn Nouvelle central-heating cooker demands a minimum chimney diameter of 7" (175mm) and a minimum height of 18' (5.5m) If there are any bends in the chimney, the internal diameter must be increased to 8" (200mm.)
XXWhen a woodstove is installed into a boat (B) or caravan, there is no option but to keep the chimney short. The safest set-up in this situation is to choose a stove with a short fluepath and a chimney that is fully insulated throughout. Generally this implies a twin-wall stainless-steel sectional flue. The result is a higher flue gas temperature than in A. This helps to compensate for the smaller volume of gases present and in most cases the draught generate will be sufficient for the more modest needs of the smaller stove.