Page 41
Installation and Operation Manual - Cape Town 1800
ENGLISH
9.4 Chimney
Location
Because the venting system is the engine that drives the wood heating system, it must have the
right characteristics. The signs of bad system design are cold back drafting when there is no fire
in the stove, slow kindling of new fires, and smoke roll-out when the door is opened for loading.
There are two guidelines to follow. First, the chimney should be installed up through the heated
space of the house, not out and up an outside wall. Second, the chimney should penetrate to
the top of the building at or near the highest heated space.
Venting systems that rise straight up from the stove flue collar provide the best performance.
Chimneys that rise inside the warm space of the house tend to provide a small amount of draft
even when there is no fire burning. This means that when a fire is lit, the smoke goes up the
chimney and strong draft build quickly as the chimney flue warms up. Chimneys that exit a
house wall and run up outside can cause problems.
Figure 12: Good System Design
Figure 13: Inferior System Design
When it is cold outside, the warm air in the house is buoyant so it tends to rise. This creates
a slight pressure difference in the house. Called ‘stack effect’, it produces a slightly negative
pressure in the lower part of the house (compared to the outside) and a slightly positive pressure
zone in the high part of the house.
If there is no fire burning in a heater connected to a chimney that is shorter than the warm space
inside the house, the slight negative pressure in the lower part of the house will compete against
the desired upward flow in the chimney.
This occurs for the two following reasons:
First, the chimney runs up the outside of the house, so the air in it is colder and denser than
the warm air in the house. And second, the chimney is shorter than the heated space of the
house, meaning the negative pressure in the lower part of the house will draw cold air down
the chimney, through the stove and into the room. Even the finest stove will not work well when
connected to this chimney.
Summary of Contents for CAPE TOWN 1800
Page 2: ......
