Carbon monoxide (CO) is an odourless, colourless gas produced when fuel burns incompletely. Wood stoves and fireplaces that are improperly installed, poorly maintained, or operated with insufficient combustion air can produce elevated CO levels inside a home. Health Canada's data on residential CO incidents consistently places solid-fuel appliances among the contributing sources. Understanding the conditions that produce CO spillage and the mechanical safeguards against it is part of responsible appliance ownership in Canada.
How Carbon Monoxide Enters Living Spaces
Under normal operation, combustion gases including CO travel up the chimney and out of the building. CO enters the living space when this flow is disrupted:
- Negative pressure inside the home — exhaust fans, range hoods, and other appliances can depressurize a tightly sealed home enough to reverse chimney draft, pulling flue gases back into the room.
- Blocked or obstructed chimney — bird nests, debris, collapsed liner tiles, or ice blockage at the chimney cap can prevent gases from exiting.
- Cracked flue liner or corroded connector pipe — gases leak into the home before reaching the chimney.
- Improperly sized flue — a flue that is too large for the appliance may not maintain adequate draft temperature, causing gases to stall and spill.
- Overly wet or green wood — wet fuel produces incomplete combustion with higher CO output and lower heat, reducing draft velocity.
Carbon Monoxide Detector Requirements in Canada
Provincial legislation requiring CO alarms in homes with fuel-burning appliances has expanded significantly since the early 2010s:
- Ontario — The Fire Prevention and Protection Act requires a CO alarm on every storey and outside all sleeping areas in dwellings with a fuel-burning appliance or an attached garage.
- British Columbia — The Fire Safety Act requires CO alarms adjacent to sleeping areas in homes with solid-fuel burning appliances.
- Alberta — The Safety Codes Act and associated fire code require CO alarms near sleeping areas in dwellings with fuel-burning appliances.
- Other provinces — Quebec, Manitoba, and Nova Scotia have adopted similar requirements in their respective fire codes.
Health Canada recommends CO detectors certified to CSA 6.19 or UL 2034. Digital display models that show current CO concentration in parts per million (ppm) provide more information than alarm-only units. CO concentrations above 35 ppm average over 8 hours are considered a health concern by Health Canada.
CO Detector Placement
Placement affects detection speed. CO is slightly lighter than air at room temperature, so detectors mounted at wall-outlet height (approximately 1 metre) or at ceiling height both work. Specific placement guidance:
- At least one detector within 5 metres of each sleeping area
- One detector on each storey of the home, including the basement
- Not directly above or beside a stove, fireplace, or furnace (avoid false alarms from normal startup CO)
- Not in areas of high humidity (bathrooms) which can affect sensor accuracy
Draft Testing and Chimney Function
Draft is the pressure difference between the flue interior and the ambient air that pulls combustion gases up the chimney. Adequate draft is necessary for the appliance to operate safely. Draft testing is part of a WETT inspection and can also be done informally by homeowners:
- Smoke pencil or incense stick test — held near the appliance door seal or air inlet, smoke drawn inward indicates negative pressure in the firebox (good draft); smoke pushed outward indicates backdraft.
- Cold chimney check before lighting — if the flue is cold and the house is warm, cold air sitting in the chimney can block draft. Warming the flue with a rolled newspaper torch held at the firebox opening for 30–60 seconds before lighting the main fire can establish initial draft.
- Manometer testing — WETT inspectors use a digital manometer to measure actual draft in Pascals. Published standards reference minimum draft values for different appliance types.
Annual Chimney Inspection and Cleaning
The National Fire Protection Association (NFPA 211, referenced by many Canadian codes) recommends annual chimney inspection for all fuel-burning appliances. Creosote — a tar-like byproduct of wood combustion — deposits on chimney walls and is a primary cause of chimney fires. Three stages of creosote are identified by chimney professionals:
- Stage 1 — Light flaky deposits. Removed by standard brushing. Normal result of regular use with dry wood.
- Stage 2 — Tar-like deposits, harder to remove. Requires professional brushing or chemical treatment.
- Stage 3 — Glazed, shiny deposits that bond to the liner. Professional removal required; may require rotary tools or chemical removers.
Burning kiln-dried or seasoned wood with moisture content below 20% (verified with a wood moisture meter) is the most effective way to limit creosote formation. Wood sold commercially as "seasoned" varies widely; moisture meters are inexpensive and provide direct confirmation before burning.
Signs of Chimney or Combustion Problems
- Smoke entering the room during or after starting a fire
- Black or tar staining around the appliance door or air inlets
- Strong odour from the fireplace when not in use
- CO alarm activating during or after appliance operation
- Difficulty establishing draft — fire starts and dies repeatedly
- Visible creosote dripping from the chimney cap or damper
Firebox and Gasket Maintenance
Door gaskets on wood stoves are fibreglass or ceramic rope seals that prevent room air from entering the firebox in uncontrolled quantities, bypassing the air control system. A failed gasket allows too much secondary air, burning fuel too quickly and reducing efficiency. The dollar-bill test checks gasket condition: close the door on a piece of paper and pull — if it slides out without resistance, the gasket requires replacement. Replacement gaskets are sold by appliance dealers and are a user-serviceable maintenance item.
Ash Removal Safety
Wood ash can hold live embers for up to 72 hours after a fire appears extinguished. Ash must be transferred to a metal container with a metal lid, never plastic or cardboard, and stored outside on a non-combustible surface away from the building until fully cooled — a minimum of 48 to 72 hours. Ash placed in household garbage bags has caused structure fires in Canada; this type of incident is avoidable with proper storage procedure.