Dead end chimnney flue (C) Daniel Friedman Dead End Flues or Dead Base Chimney Flue Hazards

  • DEAD END CHIMNEY FLUE HAZARDS - CONTENTS: What is a dead end flue or dead base chimney flue. Warnings about unsafe blocked chimney flues. Heating system & chimney service, maintenance & inspection suggestions for dead end chimneys & flues. Solutions for the Dead End Chimney or Dead Base Flue Problem.
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Definition & hazards of dead end chimneys & flues.

This article describes dead base or dead end flues and explains why they can cause heating equipment operating difficulties or why they may be unsafe. A dead end flue is one in which the flue vent connector joins at the very base of a chimney.

Debris falling down the chimney can quickly block the flue, prevent proper removal of exhaust gases from the building heating equipment, and can be dangerous. We describe how to spot dead end chimneys, how to recognize trouble signs, and what to do about dead end chimney venting systems.

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Dead End Flues or Dead Base Chimney Flue Hazards

Long flue in a crawl space (C) Daniel FriedmanDead-end flues, chimneys whose flue stops right at the point of entry of a thimble for a woodstove or heating appliance are inherently more dangerous than a conventional flue which extends several feet further past the thimble. Dead end flues are quickly and easily blocked by any debris that might fall down a chimney.

[Click to enlarge any image]

If a chimneys venting a gas-fired appliance becomes partly or totally blocked, the appliance is likely to rapidly produce very dangerous, potentially fatal carbon monoxide (CO).

Be sure that chimneys of this type are inspected and cleaned annually and be sure that you have working CO detectors as well as smoke detectors in the building.

The dead end flue in this photo (above) can be determined because we're venting that long run from a heating boiler into the bottom of a chimney that's just above ground level in a crawl space. Looks as if we've got some asbestos paper wrapping the flue - another matter to be addressed.

These articles on chimneys and chimney safety provide detailed suggestions describing how to perform a thorough visual inspection of chimneys for safety and other defects. Chimney inspection methods and chimney repair methods are also discussed.

Dead End Chimney Flue Clues & Examples

combustion backpressure burn on a boiler (C) Daniel Friedman

Abandoned dead end flue chimney in  a crawl space (C) Daniel Friedman Rusted metal heating flue (C) Daniel Friedman

Dead end chimney flues are likely to lead to the rusted-out flue vent connector such as we show here.

We suspect that the root cause of this unsafe metal heating flue is that it was routed out of the building at or below ground level - into a dead-end chimney.

Water from roof spillage or surface runoff have rusted out the flue vent connector.

This is an unsafe installation even before we think about the added hazards of fire clearances and adequate draft.

Dead end chimney or flue - dead base chimney clues (C) Daniel Friedman

Experienced heating service technicians are expected to be well aware of the hazards of dead base chimneys & flues, and as our client points out in our photograph (left), the service tech may leave a note to tip off the technician who arrives for the next service call.

To the heating service tech a dead base chimney means

At below left we illustrate another clue that may indicate a dead base chimney - no visible cleanout door below the chimney thimble where the flue vent connector attaches to the flue, and water leak stains directly below the thimble.

Dead end chimney or flue - dead base chimney clues (C) Daniel Friedman Dead end chimney or flue - dead base chimney clues (C) Daniel Friedman

Watch out: At above right we illustrate another scary problem often found in deep, hard to access crawl areas: a dead base chimney and a fallen-off or disconnected flue vent connector or "flue pipe" - presenting a fire hazard, a flue gas poisoning hazard, improper heating operation, generally an unsafe heating system.

Why would this problem be more likely here? Because the connection of the flue vent connector to the dead base chimney is deep into a hard-to-access crawl space where nobody wants to go. Be sure to inspect such locations with care.

Solutions for the Dead End Chimney or Dead Base Flue Problem

Vent Drip (C) Daniel Friedman


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