Multiple Fuel Venting
CSA B139 clause 4.2.5.10(a) for the oil-fired appliance and B365-17 clause 6.2.11 for the solid-fuel-fired appliance are supposed to prevent the installation of a solid-fuel-burning appliance that is not certified for use in conjunction with oil-fired equipment in a chimney flue serving an oil-fired appliance. It does not matter if one was there first — they cannot be on the same chimney flue. The vent systems must be separate, as for example, with two chimney flues: one for each appliance.
The British Columbia Building Code clause 9.21.2.2 allows for common venting of multiple fuels: Connections of More Than One Appliance
Except as required in Article 9.21.2.1. , two or more fuel-burning appliances are permitted to be connected to the same chimney flue provided adequate draft is maintained for the connected appliances and the connections are made as described in Sentences (2) and (3).
Where 2 or more fuel-burning appliances are connected to the same chimney flue, the appliances shall be located on the same storey.
The connection referred to in Sentence (2) for a solid-fuel burning appliance shall be below connections for appliances burning other fuels.
If you read on in the code, in clause 9.33.1.2. it states that: Solid-Fuel-Burning Stoves, Ranges and Space Heaters
1. The design and installation of solid-fuel burning stoves, ranges and space heaters, including the requirements for combustion air, shall conform to CAN/CSA-B365, "Installation Code for Solid-Fuel-Burning Appliances and Equipment."
If you then go over to the CSA B365, Installation code for solid-fuel-burning appliances and equipment, in Clause 6.2.11 it states:
“Only a solid-fuel-burning appliance certified for use in conjunction with oil-fired equipment shall be connected to a venting system serving an oil-fired appliance.”
If there is a discrepancy between the Building Code and a referenced standard, the Building Code is to be followed.
It seems here that there is a discrepancy between the Code and the Standard, but if you look at it closely you will find that there is not. Part 9.21 allows you to install multiple fuels into a common vent. Part 9.33 states that you must install a stove as per CSA B365. B365 states that you can only share a flue if the appliance is certified for such use. The only wood-burning appliances that are certified for use in conjunction with oil are combination or add-on wood furnaces. In this case, if you take these appliances and hook them up to a common vent, they must be installed as per clause 9.21 of the building code.
Clause 6.2.10 of the CSA B365-17 states:
“A solid-fuel-burning appliance shall not be connected to a chimney flue that serves a natural gas- or propane-fired appliance.”
The CAN/GSA –B149 Gas Code at clause 7.12.3 states: An appliance installed in a dwelling unit shall not be connected to a flue serving (a) a solid-fuelled appliance. Or (b) a solid-fuelled fireplace unless the opening from the fireplace to the flue is permanently closed.