Chimney issue causes carbon monoxide close call


Last winter, three children and five adults in the Fraser Valley were treated for carbon monoxide (CO) exposure, which was caused by a vent connector that had dislodged from the chimney.

First responders were called to the home after residents reported headaches and feeling ill and uncomfortable — the first warning symptoms of CO poisoning.

Technical Safety BC’s investigation traced the source of CO to a dislodged vent connector. It was discovered that the vent connector for the natural gas furnace and water heater vent was not secured to the vertical chimney by way of screws or other fasteners. It also appeared that a dirty/unbalanced furnace blower wheel or worn bearings caused excessive vibration, which caused the vent to be further dislodged (see Image 1 below). This resulted in flue exhaust gases, including carbon monoxide which is odorless, colorless, and potentially fatal, to not completely be vented outside, but to also circulate inside the home (see Diagram 1 below).

Gas appliances such as furnaces and water heaters need to be connected to an effective venting system so that all the exhaust flue gases are safely vented to the outdoors. Any connections or fittings on metallic venting systems need to be secured to each other by use of sheet metal screws or mechanical fasteners.

The takeaway? All homes should have a certified CO detector installed if you have natural gas appliances, and make sure those gas appliances are being serviced regularly, along with the venting.

Full details in our incident investigation summary. View the full listing of incident investigations here.

To learn about carbon monoxide prevention, review our gas appliances annual servicing checklist and our general carbon monoxide safety information.

Dislodged vent

Image 1: Dislodged vent. Yellow arrows point to where flue gasses were spilling from dislodged vent. The horizontal section connecting from the right is the water heater, which connects to the furnace vent.


Vertical Furnace

Diagram 1: Vertical furnace (HVAC unit).  If a furnace vent system connector becomes dislodged and allows products of combustion (which contains carbon monoxide) to directly enter the space. This exposes occupants to carbon monoxide which can be further circulated throughout the rest of the dwelling by being drawn through the return air grill or ducting then out to any room that has a warm air supply grill.

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