Chimney maintenance

Occasional inspection required

All furnaces produce combustion gases that must be vented outside your home. Although today's high-efficiency furnaces can be vented via PVC or ABS plastic pipes directly through walls, most conventional models must be vented through chimneys.

Unlike fireplace chimneys, furnace chimneys rarely need cleaning. That is not to say these units are maintenance free. They do require occasional inspection. Flue gas condensation can damage the chimney's interior wall, particularly if your chimney is on an outside wall where it is exposed to cold air.

Check your furnace chimney by inserting a mirror into the cleanout opening at its base. Look for:

  • white, powdery residue
  • flaking bricks
  • crumbling mortar joints
  • wet patches
  • damaged flue liners
  • water runoff

If you find signs of any of these problems, have your entire heating system—including the chimney—checked by a professional.

Dealing with chimney condensation

Water in your chimney could indicate a potentially serious condensation problem. Install an approved metal liner to reduce the size of the chimney flue. Exhaust gases will travel quicker up the vent and have less chance of cooling as a result. Metal liners also warm quickly, further reducing the likelihood of condensation.

The Underwriters' Laboratories of Canada (ULC) specifies different liner requirements for gas- and oil-fired furnaces. Contact your local utility or provincial/territorial technical authority for specific advice.