The fire box is required if a boiler is not used and steam is generated in the still. It can be made of metal, brick/concrete or, in some cases, earth. Its functions are to provide a base for the still and to contain the fire. The dimensions will depend on the size of the still and the fuel used. In all cases the box should allow the maximum area of the base of the still to be exposed to heat from the fire, but ensure that no part of the base of the still that does not have water above it is exposed to direct heat of the fire.
For tea tree, the cheapest fuel is dried leaf after the oil has been extracted. This requires a fire box about 1 metre high. While the fuel is cheap and available, the necessity for constant stoking makes use of this fuel unattractive in most circumstances. For wood fuel the box needs to be about 500mm high, while for an oil burner 300mm is sufficient. The "box", which has neither top nor bottom, requires one side to be open to allow stoking of solid fuel, or to have an aperture to take an oil or gas burner. At the opposite end an aperture to take a flue is necessary. In the case of using an oil burner a baffle is required to distribute the flame from the burner so that it impinges on the base of the still instead of going directly up the flue.
The flue of at least 150mm diameter needs to be carried horizontally 3 or 4 metres from the still to reduce smoke and heat near the still and then vertically about the height of the still to cause a draught, or a straight flue can be set at an angle to achieve the same effect. A tall flue, while more effective in getting smoke away from the still, causes too much draught, so dragging too much heat from the fire box. It is possible in some sites to set up a still by excavating a fire-box in the earth and having no made-up fire-box at all. However a flue is essential for comfortable operation of the equipment.
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