How to Repair a Furnace Flue

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Things You'll Need

  • Tape measure

  • Cordless drill

  • Galvanized sheet-metal ductwork

  • Snips

  • Pipe crimper

  • Sheet-metal screws

  • High-temperature silicone caulk

  • Caulk gun

  • Gloves

A furnace flue directs the poisonous products of combustion out of your home. It typically runs from the furnace to a chimney. The gases it exhausts are hot and moisture-laden. Since a furnace flue is made from galvanized ductwork, it corrodes over time once the galvanized coating breaks down. When a furnace flue corrodes, poisonous gases invade your home, so it's best to repair a furnace flue by replacing damaged piping before it corrodes completely.


Step 1

Turn your furnace off. This prevents flue gases from entering your home during the repair.

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Step 2

Remove the damaged flue pipe out of the piping system by pulling each connection apart.

Step 3

Measure the length of the damaged flue pipe and cut a replacement at that measurement. Crimp one end with your pipe crimper.


Step 4

Slide the new piece of flue pipe into place and push the connections back together.

Step 5

Install three to four sheet metal screws at each connection and caulk with high temperature silicone caulk.


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