Myriad II Installation and Operation Manual
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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
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
Only a wood stove certified and labelled as ‘mobile home approved’ may be
installed in a mobile home. Wood stoves installed in mobile homes must have a ducted
supply of combustion air from outdoors. This air supply should be routed down through the
house floor into the vented crawl space under the mobile home. The air supply duct should
be non-combustible aluminum flex duct with a screened weatherhood on the outside end.
Note: Fabric duct may also be used, provided it is suitable for HVAC use and meets the
requirements of CAN/ULC S110 or UL 181 Class 1 standards. It must have a non-
combustible insulation and be corrosion resistant.
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 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.