Danger: Backdrafting

Fuel burning equipment, like woodburning and natural gas fireplaces, natural gas or oil furnaces, or natural gas water heaters, need a source of air to operate safely and efficiently. Appliance vent backdrafting occurs when there is insufficient air for the combustion process. When properly adjusted and vented, the combustion of natural gas produces carbon dioxide and water vapour, the very same things that we exhale. However, if there is insufficient air for fuel burning equipment, or if a chimney or vent is blocked, then these combustion products spill into the house and may contain significant amounts of carbon monoxide. Carbon monoxide is an odourless, colourless, tasteless gas which is very toxic.

Some of the precautions you can take to prevent this hazard include:

Never tamper with fuel burning equipment, vents, flues, or fresh air intakes.

  • Never insulate or try to seal up a draft hood, wind cap, or exhaust vent on any natural gas fuel burning equipment.
  • It is absolutely essential for your safety that panels and grills on the furnace be kept in place and that the fan compartment door be closed when the furnace is operating.
  • If you have a natural gas water heater, make sure that combustion air openings at the bottom of the tank and the opening below the draft diverter (on top of the tank at the flue duct) remain unblocked. Do not store anything on top of or around your natural gas water heater!
  • For all fuel burning equipment, make sure that vent hoods and pipes are securely in place and that external vents and chimneys are not blocked by insulation, leaves, or bird's nests.

If backdrafting is occurring with a wood-burning fireplace, you must either open a nearby window during operation or install a supply of outside combustion air for the fireplace. A heating contractor can advise you and install this ducting. If backdrafting is occurring with natural gas-fired equipment, turn off the equipment and contact your local Technical Standards and Safety Authority (TSSA) registered heating contractor.

How can you identify backdrafting?

  • If you detect stuffy, stale, or smelly air (e.g. the smell of something burning) on a regular basis in the winter.
  • If you have difficulty lighting a wood-burning fireplace and smoke is coming into the room instead of going up the chimney (especially when the clothes dryer, kitchen downdraft cooktop, or an exhaust fan is in use).
  • If you can see black soot on the wood-burning fireplace stonework.
  • If the burner flames are mostly yellow instead of clear blue on natural gas-fired equipment, such as the furnace, water heater, or other natural gas-fired equipment.
  • If the pilot light on the natural gas furnace, water heater, or other gas-fired equipment continually goes out.