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1.9 Draft conditions
If smoke spillage occurs when the fire door is opened, it is probably due to poor chimney draft.
This type of stove requires at least 12 pa of chimney draft to achieve satisfactory combustion
and smoke spillage prevention. However, in cases where the stove door is opened too vigorously
you could expect that slight smoke spillage may occur.
The flue gas temperature at the rated output is 361˚ C relative to 20˚ C. The flue gas flow is 8.9
gr/sec.
Draft conditions:
The chimney’s draft is the resulting effect within the flue caused by the difference in
temperature within the flue and the cooler temperature outside. Other factors that can
influence the level of draft include the length of the flue, insulation of the chimney,
adverse weather conditions or tall buildings or trees nearby the flue terminal.
Poor draft occurs when:
• The atmospheric temperature difference is too low, e.g. a poorly insulated chimney.
If the chimney is excessively cool, it may help to ‘prime’ the flue before the fire is
lit. just place a screwed-up sheet of newspaper in the flue-ways of the stove and
ignite.
• The outside temperature is too high, e.g. during the summer months.
• There is no air movement (wind) outside.
• The chimney is not tall enough, with the result that the terminal sits in the lee of
the roof surface or in the vicinity of tall trees or neighbouring buildings. These con-
ditions are also associated with downdraft where the flue gases are pushed back
down the chimney.
• Flue draft is diluted by residual air entering the chimney, e.g. due to inadequate flue-
pipe joints or leaks at the cleaning door or flue collar.
• Unsealed, unused fireplaces are connected to the chimney.
• The flue is blocked, e.g. by soot, due to inadequate cleaning, loose debris or even
a birds nest.
• The house is too tightly sealed (see section on Fresh air supply).
A good draft is achieved when:
• The temperature difference between the chimney and outside is high. This also ap-
plies during firing, when the need is greatest.
• The weather is clear and there is a good wind.
• The chimney is of the proper height, i.e. minimum 4 meters over the stove and the
termination adequately clear of the roof line.
If you have any doubts, you may want to have your installer measure the draft in the chimney.
