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1.8 Draught
If smoke comes out of the stove when the fire door is opened, it will be due to the poor draught
in the chimney. This type of stove requires at least 12 PA of chimney draught to achieve satis-
factory combustion and to prevent smoke from escaping. Smoke may, however, escape in any
event if the stove door is opened during vigorous firing, so this should be avoided.
The flue gas temperature at the rated output is 275°C relative to 21°C.
The flue gas mass flow is 8.8 grammes/second.
If in doubt, you may want to get your chimney sweep to measure the draught in the chimney.
Draught
The draught in the chimney is the result of the difference between the high tempera-
ture in the chimney and the cooler temperature outside. Other factors that determine
whether sufficient negative pressure can be produced to create a draught include the
length and insulation of the chimney, and wind and weather conditions.
the draught will be reduced when:
- The temperature difference is too low, e.g. in connection with a poorly insu-
lated chimney.
If the chimney is cold, it may help to light (burn up) a rolled-up newspaper in
the chimney’s cleaning door.
- The outside temperature is too high, e.g. during the summer.
- There is no wind.
- The chimney is not tall enough, with the result that it sits in the lee of the roof
surface or tall trees.
These conditions are also associated with the greatest risk of smoke coming
back down the chimney.
- Air is entering the chimney in undesired places, e.g. through cracked joints or
leaks in the cleaning door or the flue pipe.
- Unsealed, unused fireplaces are connected to the chimney.
- The flue pipe and chimney are clogged up with soot due to inadequate cleaning.
- The house is too tightly sealed (please see the section on Fresh air supply).
A good draught is achieved when:
- There is a big difference between the temperature in the chimney and outside,
i.e. when the need for heating is greatest.
- The weather is clear and there is a good wind.
- The chimney is of the proper height, i.e. Minimum 4 metres above the stove,
and clear of the spine of the roof.
