An Introduction to Your Chimney
Your chimney’s job is to remove combustion gases from your home. However, your chimney won’t work
properly if it is poorly designed, poorly installed or poorly maintained.
There are many causes of inadequate chimney performance or failure. Here are some examples:
• A chimney may be improperly sized — too small for the job or too large to maintain an adequate draft.
• Obstructions such as bird and wasp nests, broken bricks and ice can block a chimney’s air flow.
• Corrosion may become a problem as a result of condensation or poor construction or installation.
• An uninsulated chimney on an exterior wall is a particular concern because it can become very cold
when combustion gases are not present. This can lead to condensation of moisture from the air. When
the chimney first fills with moist combustion gases, the condensation may increase, at least until the
chimney warms up. Condensation can result in damage to the materials in the chimney and ice
formation. This in turn leads to problems such as crumbling bricks, cracks and leaks, blockages, and
poor draft.
Inspect and Maintain Your Chimney
A blocked chimney will not vent your furnace’s combustion gases. Have a professional check that your
chimney is not cracked and is clear of obstacles such as pieces of broken brick, or ice, or dead birds. This
check should be done routinely as part of an annual or bi-annual service call.
Determine the Extent of Chimney Damage and the Safety of the Entire Chimney Flue
First, you will want to be absolutely sure that the chimney damage, whether to the ceramic clay flue liner or to
the surrounding masonry or both, is limited to the upper, visible, accessible part of the chimney.
Other chimney damage lower in the chimney itself as it passes through or alongside the building could
be very dangerous, even fatal if carbon monoxide or other flue gases leak into the building or if sparks
cause a fire.
We suggest that you hire a professional chimney sweep who can examine the entire flue. Most chimney
sweeps also offer repair services, and can suggest what repairs are needed and give alternatives for the
particular chimney and flue on your building.
Item #
Chimney Defect, Concern, Hazard
1
Chimney cap and crown defects: missing chimney cap, damaged chimney crown
or top seal, leaks into the chimney leading to rust damage on metal flues or frost and
water damage to masonry flues, leading to an unsafe chimney.
2
Creosote or heavy soot in chimneys: a possible chimney fire hazard, especially at
wood-burning fireplaces or woodstove flues
3
Chimney thimble ports abandoned or hidden, covered-over by drywall,
wallpaper, or a simple metal "pie-plate" enclosure - a fire and flue gas leakage
hazard.
4
Cleaning: chimney has not been cleaned for a protracted time; risks are greater for
oil-fired equipment and for fireplaces & woodstoves.
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5
Damaged, blocked, or unsafe chimney flues: a damaged chimney flue risks leaking
dangerous combustion gases into the building or risks sparks which could start a
building fire. Movement and cracks in a masonry chimney, rusted metal flues,
unlined single-brick wythe flues, water leaks through chimneys, frost damaged
chimney clay flue tiles, missing or open chimney cleanouts, dead-end flues, are
examples.
Look for conditions likely to rust a metal flue; look for conditions likely to cause
cracking, breaking, or spalling of clay flue liners. Look for improperly constructed
clay-tile lined masonry chimneys leaving concrete between joints that prevents
thorough chimney clearing, or causing leaks and frost damage to the chimney flue or
chimney structure.
6
Dead end flues - a chimney that is entered by a flue vent from a heating appliance,
woodstove, or similar device right into the very bottom of the chimney flue.
Common in older homes, such flues are easily blocked by falling debris - an unsafe
condition.
7
Fireplace inserts for wood or coal installed into an existing masonry flue without
chimney inspection and if needed, re-lining.
8
Inspection: chimney has not been inspected for safety or cleanliness for some
protracted interval
9
Missing chimney cleanout doors, open cleanout doors: a fire hazard as well as a
cause of improper, unsafe heating appliance operation
10
Movement in chimneys, especially masonry chimneys: a dangerous condition,
movement can cause hidden cracks and breaks that make a chimney unsafe, risking
flue gas leakage into the interior or causing a building fire.
11
Orphaned gas-fired water heaters not venting into any chimney, or a gas-fired
water heater venting alone into a large masonry flue. The water heater may never
develop sufficient heat in the old masonry flue to establish a working draft - flue
gases spill backwards into the building, an unsafe condition.
12
Rusted or damaged chimney or fireplace components: rusted, damaged,
inoperative or missing fireplace dampers. Examples include a damper that has rusted
through, a metal damper enclosure in the chimney throat rusted through, a metal
fireplace insert rusted out at the chimney base.
13
Unlined chimney flues in single-brick wythe chimneys of older homes - a fire and
flue gas leakage hazard
14
Un-sealed flue-vent connectors at chimney thimbles: metal flues not sealed in the
thimble, missing thimble, risking flue gas leaks or sparks; common at woodstove and
heating system metal flue connections into a masonry chimney.
15
Unsafe fire clearances between metal flues or other types of chimneys and nearby
combustibles
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