Chimney location affects performance (C) Carson Dunlop Associates Diagnose & Correct Chimney Draft & Performance Problems

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Chimney draft troubleshooting:

This article describes how the location of the chimney on an exterior wall, imbedded in the wall, or located inside of the building affects chimney draft and performance.

How to diagnose poor chimney draft for a smoky fireplace, woodstove, or heating boiler/furnace. 18 things to check if your chimney has bad draft or your fireplace is smoky. Draft: Thermal Performance of Chimneys - How to correct inadequate chimney draft.

Our sketch of types of chimney placement on a building is courtesy of Carson Dunlop Associates. These articles on chimney construction, design, troubleshooting, cleaning & repair include description of how to perform a thorough visual inspection of chimneys for chimney safety, draft, chimney fire hazards, chimney collapse hazards and other defects.

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Chimney Location, Draft & Performance

Chimney location affects performance (C) Carson Dunlop Associates

As Carson Dunlop Associates [at REVIEWERS] sketch shows, a warm chimney works best at developing good draft which in turn helps assure that the appliances or fireplaces being vented by the chimney will perform properly.

Construction of the chimney running through the interior of a home was originally done to get the most heat out of the chimney in cold weather.

Even though it is easier to build the chimney on the outside wall of a building, a central chimney provided heat through its masonry to the building interior on all floors.

[Click to enlarge any image]

Draft: Thermal Performance of Chimneys

A chimney's thermal performance provides the "draft" by maintaining a warm interior lining. The draft is the pressure difference between ambient air and the less dense flue gases within the chimney. The lighter gases are buoyant and rise to be displaced by heavier ambient air.

The chimney must contain the hot gases and protect the surrounding materials against combustion. Residential masonry chimneys must protect the building while under exposure to 1000°F continuous flue gas temperature although most gas appliances operate with a flue gas temperature of about 300°F and oil burners with a flue gas temperature of about 500°F.

19 Causes of Poor or Inadequate Chimney Draft, Draw, or Causes of Smoking Fireplaces & Heaters

Metal chimney too short (C) Daniel Friedman

The vertical distance from the top of this chimney to the top of the oil fired heating boiler it serves is less than six feet.

The oil fired boiler has blown soot into the utility room and garage throughout its' life, a constant source of annoyance that probably stems from inadequate total draft even when the oil burner, boiler, and chimney flue are up to full operating temperature.

Opening found in chimney making it unsafe (C) Daniel FriedmanSee Chimney Too Short



We could address this short chimney with a draft inducer fan, but a taller flue would be smart anyway, to get the chimney top higher than the roof surface. We discuss draft inducer or "draft boosting" fans for heating systems (and maybe for some fireplaces) in detail at DRAFT INDUCER FANS

The articles listed below assist in diagnosing other causes of poor chimney performance.

Photo above: During a 1986 restoration of an home in the Bleachery in Wappingers Falls, NY, built ca 1865, the author / renovator wanted to be sure the chimney was in good condition, as the chimney was in active use by a gas-fired heating boiler.

Watch out: improperly-sealed holes in in-use chimneys are unsafe, risking a building fire or dangerous flue gase leaks, even fatal carbon monoxide gas leaks.

We cut away drywall boxing in the chimney at a height where marks on the drywall suggested a previous passage of a wood-stove flue. The chimney thimble had been "sealed" using a clip-in tin pie-plate cover that had rusted away.

In the second photo (below) you can see that I repaired two openings in this brick chimney before boxing it in in preparation for installing finished wall surfaces.

Wall cavity at chimney showing chimney repairs before adding insulation (C) Daniel Friedman 28 West Street Wappingers Falls ca 1986Photo above: the author was boxing in the repaired brick chimney in a home in Wappingers Falls, NY.


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