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8.4.2 Why the Chimney Should Penetrate the Highest Heated Space
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.
8.5 Supply of Combustion Air
In Canada, wood stoves are not required to have a combustion air supply from outside, except
for mobile homes. Research has shown that outside air supply do not compensate for the
depressurization of the house and may not be sufficient to provide a supply of combustion air in
windy weather. However, to reduce the risks against smoke spillage due to house depressurization,
a carbon monoxide (CO) detector is required in the room where the stove is installed. The CO
detector will provide warning if for any reason the wood stove fails to function correctly.
8.5.1 Combustion Air Supply in Mobile Homes
This stove is 'mobile home approved'. It must therefore have a supply of combustion air from
outdoors. The air intake must not draw air from the attic, from the basement, from a garage or
any enclosed space. Air must be drawn from a ventilated crawl space under the floor or directly
from outside. Install a flexible or rigid, insulated pipe (HVAC type, must comply to ULC S110
and/or UL 181, Class 0 or Class 1) to the fresh air intake.
Where a mobile home has been converted to a standard house by mounting it on a permanent
basement foundation, the supply of outdoor air is not required.
8.5.2 Air Supply in Conventional Houses
The safest and most reliable supply of combustion air for a wood stove is from the room in which
it is installed. Room air is already preheated so it will not chill the fire, and its availability is not
affected by wind pressures on the house.
Installation and Operation Manual - Solution 2.3
Figure 34: Chimney location in the house
Page 43
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