Pyropak Installation and Operation Manual
37
There are two reasons why the
chimney in the house at right will
cold backdraft when it is cold
outside and there is no fire burning
in the stove. 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 low
in the house will pull outside 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 supply of combustion air from outdoors
(except in mobile homes) because research has shown that these supplies do not give
protection against house depressurization and may fail to supply combustion air during
windy weather. However, to protect against the risk of smoke spillage due to house
depressurization, a carbon monoxide (CO) detector/alarm is required in the room in
which the stove is installed. The CO detector will provide warning if for any reason the
wood stove fails to function correctly.
8.5.1 Air Supply in Conventional Houses
The safest and most reliable supply of combustion air for your 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. Contrary to commonly
expressed concerns, almost all tightly-sealed new houses have enough natural leakage to
provide the small amount of air needed by the stove. The only case in which the wood
stove may not have adequate access to combustion air is if the operation of a powerful
exhaust device (such as a kitchen range exhaust) causes the pressure in the house to
become negative relative to outdoors.
Some jurisdictions in the United States require that wood stoves have a supply of
combustion air from outdoors. If you do install an air supply through the wall of the house,
be aware that its pressure can be affected during windy weather. If you notice changes in
wood stove performance in windy weather, and in particular if smoke puffs from the stove,
you should disconnect the outdoor air duct from the stove and remove the duct. In some
windy conditions, negative pressure at the duct weatherhood outside the house wall may
draw hot exhaust gases from the stove backwards through the duct to outdoors. Check the
outdoor air duct for soot deposits when the full system is cleaned and inspected at least
once each year.
