Seal Your Flue Pipes: Homeowners Clinic

• homeowners clinic
• heating

My house is heated with a gas-fired furnace. How can I seal the house's ducts to prevent carbon monoxide (CO) leakage?

First, let's clarify this. Ducts carry heated or cooled air. Under normal operation, they don't carry combustion byproducts and are sealed as a matter of energy efficiency, not combustion safety. Sheetmetal flue pipes, on the other hand, carry combustion gases from the furnace or the boiler to the chimney. They are not sealed to the same extent that ducts are.

Fiberglass ducts require an aluminum foil tape, while sheetmetal ducts are sealed with metal-foil tape, professional-grade duct tape or mesh-reinforced mastic.

Single-wall sheetmetal flue pipes are joined without sealants. The end of one flue pipe is crimped and fitted into the end of the next (uncrimped) pipe. The joint is fastened with three sheetmetal screws. If you find gaps in the flue pipes or if they are loose, call a heating-cooling professional, advises Pat Porzio, a mechanical contractor in Haskell, N.J., and a Popular Mechanics contributor. Don't try to remedy the problem yourself.

Finally, install CO detectors throughout the house in bed-rooms, family rooms and finished basements.

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