hergom H-03 Serie Instructions D'installation, De Service Et De Maintenance page 32

What is the "chimney draw"?
The tendency air has to rise generates the chimney effect.
When a FIREPLACE is lit, hot air rises through the chimney. The chimney flue
heats up and keeps it drawing. Until the fireplace and the chimney are hot enough, the
chimney effect will not work properly.
The chimney effect depends on the location, size and height of the chimney.
The following must be taken into consideration:
- Chimneys located inside a house keep warm and, therefore, chimney draw is
greater.
- The chimney size recommended by the manufacturer will provide a good chimney
effect.
- The height of a chimney affects how it draws:
The chimney must project at least one metre over the highest part of the roof.
Other factors also affect chimney draw:
- Houses that have very good internal insulation, free from draughts, provide
inadequate draw as no air enters the building. This can be corrected by allowing external
air to reach the FIREPLACE
- High trees and/or buildings near the house also have a negative effect on chimney
draw.
- Wind speed. Usually, sustained strong winds increase chimney draw but stormy
winds have a negative effect.
- External temperature. The colder it is outside, the greater the chimney effect.
- Atmospheric pressure. The chimney effect is usually poor on rainy, damp or
stormy days.
- Intensity of the fire. The hotter the fire, the stronger the chimney effect.
- Cracks in the chimney, badly sealed or dirty doors, air entering through pipe joints,
other devices connected to the chimney.... may have a negative effect on chimney draw.
2. - Creosote formation and cleaning.
When wood burns slowly, it produces tar and other organic fumes that, when
combined with a damp atmosphere, form creosote. Creosote fumes may condense if the
chimney walls are cold. If it catches fire, extremely tall fires may be caused. Any
accumulation of creosote must be eliminated.
As the accumulation of creosote depends on a number of variables, it is very
difficult to know when the chimney should be cleaned.
The safest way of ensuring that the chimney of your fireplace is creosote free is by
performing a visual inspection.
Consequently, we recommend building installations that are easy to access.
3. - Options
If you are going to build a chimney for your Built-in Fireplace H-03, you have two
alternatives:
a) Brickwork chimneys.
b) Metal chimneys.
greater height  better chimney effect
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