Sloping masonry chimney (C) Daniel Friedman Detection & Inspection of Angled or Sloped Chimney & Flues

  • ANGLED CHIMNEYS - CONTENTS: How to spot a sloped or angled chimney or chimney flue on a building & how to recognize & report safety or functinoal defects in these sloping chimneys. Issues with angled chimney flues - proper cutting of clay flue tiles for an angled flue; maximum angle for sloping chimney flues
  • POST a QUESTION or READ FAQs about angled or sloped masaonry chimneys & flues

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Angled chimneys & sloped flues: this article explains the hazards of angled or sloped masonry or metal chimneys and chimney flues.

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.

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Angled and Offset Chimney Flues - Specifications & Concerns with Sloping Chimneys & Flues

Offset flue specifications (C) Carson Dunlop AssociatesThis article series describes chimney defects and hazards that can be observed from on-roof access, including damage to a masonry chimney top, antennas mounted on chimneys, and angled chimney flue hazards.

Our photo at page top shows a chimney that was angled severely beginning at the attic floor - look there for cracks that may have opened, forming a fire and gas hazard.

Offset or angled chimney flues are found in both masonry and metal chimney installations.

Especially where multiple flues are routed inside of a single large masonry chimney or inside of a single wood-framed chimney chase, it should not be a surprise to discover that one or more of the appliances venting into one or more of the flues has to send its gases up at an angle to reach the final vertical section of flue in the chimney.

Look for these clues that may indicate angled chimney flues that deserve further inspection:

  • Large masonry chimney with two or more internal flues, serving one or more fireplaces.
  • Large chimney chases serving two or more metal flues with one or more fireplaces installed in the building.
  • View down a large masonry chimney from roof top that shows flues angling off to fireplaces or other building flues
  • Chimneys in attics that have been excessively corbelled or leaned to one side
Clay flue tile liners mitered when on angle (C) Carson Dunlop Associates

Just as we reported that a clay tile lined chimney would be difficult to clean due to projecting concrete between vertically-stacked clay chimney tiles, clay tiles need to be cut properly when constructing an angled chimney such as the one shown in Carson Dunlop's sketch.

The sketches shown at left shows the concern with proper miter joints in a sloping masonry chimney flue.

[Click to enlarge any image]

Only the bottom design, showing that the clay chimney tile was cut on an angle, is correct.

The top two designs risk both cleaning difficulties and also water, smoke, soot,or creosote leaks into the chimney structure.

Offset flue specifications (C) Carson Dunlop AssociatesThe next Carson Dunlop sketch at left shows that a masonry flue is limited to 30 deg. offset, or in some jurisdictions, 45 degrees of offset while a metal flue may, in some areas, be permitted to slope to 60 degrees of offset.

In sum, concerns about angled or sloping chimneys and chimney flues include:

  • Protruding or improperly cut clay flue tile liners that leak or that obstruct cleaning
  • Too-flat low slope chimney flues may accumulate ash, soot, creosote, leading to a blocked flue and requiring extra cleaning measures
  • Metal chimney flues also cannot be sloped too gently nor for too great a distance or draft and clogging problems occur.

    A metal chimney might be permitted to run at angle of up to 60 deg. of slope in some jurisdictions.

    See TRIPLE-WALL METAL FIREPLACE CHIMNEYS for additional sketches and details about angled or sloping metal chimneys and flues and for a fireplace metal chimney inspection checklist.

Support Rules for Sloped Chimneys & Elbows in Metal Chimneys & Flues

If elbows are used in the chimney the slope cannot be less than 30 degrees, and the sloping segment of the chimney above each elbow must be supported by straps or other means specified by the chimney manufacturer.


Continue reading at CHIMNEY LEANING, SEPARATION, MOVEMENT or select a topic from the More Reading links shown below.



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ANGLED CHIMNEYS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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