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10.6 Minimum Chimney Height
The top of the chimney should be tall enough to be above the air turbulence caused when
wind blows against the house and its roof. The chimney must extend at least 3 ft. (1 m) above
the highest point of contact with the roof, and at least 2 ft.(60 cm) higher than any roof line or
obstacle within a horizontal distance of 10 ft. (3 m).
10.7 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 insert, slow kindling of new fires, and smoke roll-out when the door is open for loading.
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 insert and into the
room. Even the finest insert will not work
well when connected to this chimney.
Figure 33: Chimney location in the house
Page 37
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