How to Cut a Flue Once it Has Been Joined

Cutting a vent pipe once it's installed requires tin snips.

A flue is a metal pipe that is used to move exhaust products, from combustion appliances to the outside of the building. This pipe is important for the safety of a building because the gases inside are both hot and poisonous. You may need to cut an existing flue to add a vent dampener, draft inducer or to add another appliance to the flue. Turn the power off to any device attached to the vent before starting any work.

Things You'll Need

• Marker
• Drill
• 3/4 inch metal bit
• Tin snips

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Instructions

1. Turn the power off for the appliances attached to the vent at the distribution panel.

2. Draw the opening you want to cut in the flue with a marker. Double-check the markings are accurate by measuring them twice.

3. Drill a hole in the center of the marking with a 3/4-inch metal bit and drill. If the shape you are cutting is a square, drill four holes near each corner.

4. Cut the vent pipe along the lines with tin snips, starting at the drilled holes. Make sure your cuts are accurate. If you cut outside the lines, you will need to replace the pipe and start over.

Tips & Warnings

• Contact your local building authority to check if the modifications you are making to the vent system meet local building codes.

• Don't use the appliance while the vent pipe is compromised. This will vent poisonous gasses into the building.

References

• Field Controls: Draft Inducer Installation Instructions