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Another essential criterion is meeting the flue draught requirement.
This depends on three major factors.
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HIMNEY CHARACTERISTICS The requirements for minimising the draught loss in the chimney are:
• Good thermal insulation to avoid the flue gases cooling down too
quickly.
• Smooth interior surface to reduce the flow resistance.
• Chimney well-sealed to avoid outside air leaking in. Air penetra-
ting from the outside speeds up the cooling of the flue gases.
These requirements correspond to chimneys of the type according
to DIN EN 13384-1: 2003-03 “Thermal and fluid dynamic calculation
methods”.
Free-standing chimneys require particularly good insulation.
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HIMNEY DIMENSIONS The system may only be connected to a chimney which has been di-
mensioned in accordance with DIN EN 13384-1, taking into account
the fuel planned and the expected load, and which meets local buil-
ding regulations for the installation site.
A chimney can only be designed with full knowledge of the on-site
conditions. This includes taking into account the following factors:
• Location of the house
– Surrounding hills/slopes
– Wind direction
• Location of the chimney in the roof
– The opening of the chimney must be at least 0.5 m above the
highest edge of roofs with a slope of more than 20° or at least
1.0 m higher than roof surfaces which slope at 20° or less.
• The effective height of a chimney is measured from the entrance
into the flue to the end of the chimney.
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ONNECTING THE BOILER TO
THE CHIMNEY
The boiler must be connected to the flue with a connecting piece
which is as short as possible, at an angle which is less than 30-45° to
the chimney.
You should aim for a connecting piece with a maximum length of 1
m using just one fitting. Every additional fitting results in a greater
pressure loss in the exhaust path and should thus be avoided. The
same is true for overlong connecting pieces. If, for constructional re-
asons, they have to be longer than 1 m, they should be adequately in-
sulated (at least 5 cm of mineral wool or equivalent material) and, if
possible, should be fitted with an upward inclination.
When planning the flue system, a flue calculation based on DIN EN
13384-1 must be performed by authorised specialists.
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