Fumes heat up during combustion, increasing their volume. Their density is therefore lower than the one of the surrounding colder air.
This difference between the inside and outside temperatures of the chimney results in a negative pressure which increases proportionally to the vent pipe length
and the temperature.
The draught must be stronger than the fume circulation resistance so that all exhaust fumes generated during combustion inside the stove are drawn upwards
through the outlet and the vent pipe. Many weather conditions affect the vent pipe functioning, such as rain, fog, snow, altitude, and wind being the most important
as it can create both negative pressure and dynamic loading.
The wind action varies depending on whether it is ascending, descending or horizontal.
•Ascending wind always results in an increased negative pressure and draught.
•Horizontal wind results in an increased negative pressure as long as the chimney cowl was properly installed.
•Descending wind always diminishes the negative pressure, sometimes inverting it.
Excess draught causes an increase in the combustion temperature and consequently a loss in stove efficiency.
A part of the combustion fumes is drawn up through the vent pipe together with small pellet particles before combustion reducing stove
efficiency, increasing fuel consumption and resulting in the emission of polluting fumes.
At the same time the high fuel temperature, due to an excess amount of oxygen, wears down the combustion chamber sooner than
expected.
On the other hand, poor draught slows down combustion resulting in a decrease in the stove temperature, fume spillage inside the room,
a loss of stove efficiency and dangerous build-up in the vent pipe.
In order to avoid excessive draught it is appropriate to use:
Draught regulator
02.3 STOVE EFFICIENCY
Highly efficient stoves may pose difficulties for fume extraction.
In order for a vent pipe to work properly its internal temperature must increase as a consequence of the fumes
generated during combustion.
Importantly, the efficiency of a heater is determined by its ability to transfer most of the heat produced to the
environment to be heated: consequently, the greater the efficiency of the stove, the "colder" the residual fumes of
combustion, and consequently, the lower the "draft".
A traditional chimney flue, with a rough design and insulation, is more efficient if used with a traditional open fireplace
or a poor quality stove where most of the heat is lost with the fumes.
Therefore, purchasing a quality stove often entails modifying the existing chimney flue to obtain a better insulation,
even when it already works properly with old appliances.
Poor draught results in the stove not operating when hot or in smoke spillage.
•Connecting the stove pipe to an existing chimney flue that has already been used with an old appliance is a
common mistake. In this way two solid-fuel appliances share the same chimney flue, which is wrong and
dangerous.
•If the two appliances are used simultaneously, the fume load might exceed the existing chimney flue capacity resulting in downdraught. If only one appliance
is used, the fume heat will facilitate draught but the cold air coming from the other appliance not in use will cool down exhaust fume temperature again blocking
the draught.
•Besides the problems described so far, if the two appliances are placed on different levels the communicating vessel principle might be interfered with, causing
combustion fumes to be drawn in an irregular and unforeseeable way.
03. WARNINGS ISTALLATION
Using coaxial tubes the air will be pre-warmed contributing to improved combustion and lower
emissions into the atmosphere.
Follow the instructions before installing your stove.
Select the position where the stove is to be installed and:
•Arrange the connection to the vent pipe for fume extraction
•Arrange the external air intake (combustion air)
•Arrange the connection to the earthed mains
•The electrical system of the room where the stove is to be installed must be earthed,
otherwise the control board may not work properly.
•Place the stove on the floor in a convenient position for the connection to the vent pipe
and close to the combustion air intake.
•The appliance must be installed on a floor with an adequate load-bearing capacity.
•Should the existing floor not comply with the requirement above, proper measurements
must be taken (for instance, the installation of a load distribution plate).
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