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CHIMNEY INSPECTION DIAGNOSIS REPAIR
Abandoned Chimneys - Indoor Inspection
Abandoned Chimneys: Outdoors
Angled Chimney Flues
ARCHITECTURE & BUILDING COMPONENT ID
Attic Chimney Inspection
BACKDRAFTING HEATING EQUIPMENT
Blocked Chimney Flues
Bracket Chimney Collapse & Fire Risks
B-Vent Clearances Table
CARBON MONOXIDE - CO
CHIMNEY CAP & CROWN
CHIMNEY CHASE Construction & Defects
Chimney Cleaning Advice, Procedures
Chimney Cleaning Fraud Warning
CHIMNEY CLEANOUT DOORS
Chimney Components Definitions
CHIMNEY COLLAPSE Risks, Repairs
Chimney Crack Detection & Diagnosis
Chimney Draft & Performance
CHIMNEY FIRE ACTION / PREVENTION
CHIMNEY FLASHING Mistakes & Leaks
CHIMNEY HEIGHT & CLEARANCE CODE
CHIMNEY HEIGHT EXTENSIONS
Chimney Inspection Checklist
Most Frequent Chimney Defects
Chimney Inspection Checklist - Outdoors
Chimney Inspection Checklist - Indoors
Responsibility of an ASHI Home Inspectors
CHIMNEY INSPECTION, FLUE INTERIOR CHIMNEY INSPECTION CAMERA
CHIMNEY INSPECTION INDOORS
CHIMNEY INSPECTION from GROUND CHIMNEY INSPECTION at ROOFTOP
CHIMNEY LEANING, SEPARATION, MOVEMENT CHIMNEY REPAIR FRAUD WARNING
CHIMNEY REPAIR METHODS
Chimney Safety - CPSC Alert
Chimney Shoulder Leaks
Chimney Shroud, Decorative
Chimney Spalling, Exterior
CHIMNEY TYPES & MATERIALS
COMBUSTION AIR DEFECTS
COMBUSTION AIR for TIGHT buildings
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
COMPLETE COMBUSTION, Stoichiometric
CREOSOTE FIRE HAZARDS
Curved Brick Chimneys - Sulphation
Dead End Chimney Flue Hazards
DIRECT VENTS / SIDE WALL VENTS
DRAFT HOODS - gas fired
DRAFT MEASUREMENT, CHIMNEYS & FLUES
DRAFT REGULATORS, DAMPERS, BOOSTERS
EFFLORESCENCE, Salts & White / Brown Deposits
EMERGENCY RESPONSE, IAQ, GAS, MOLD
FIRE CLEARANCES INDOORS
FIRE CLEARANCES for MASONRY CHIMNEYS
FIRE CLEARANCES, METAL CHIMNEYS
FIRE CLEARANCES, SINGLE-WALL METAL FLUES
FIRE CLEARANCE WOOD & COAL STOVE FLUES
FIREPLACES & HEARTHS
FIRE STOPPING in BUILDINGS
FLAME COLOR, BLUE vs YELLOW COMBUSTION
FLASHING, CHIMNEY Mistakes & Leaks
FLUE SIZE SPECIFICATIONS
Flue Separation Requirements
Flue Tile Damage in Chimneys
FLUE VENT CONNECTORS, HEATING EQUIPMENT
FUEL CHANGES for HEATING APPLIANCES
HEATING COST FUEL & BTU Cost Table
HEATING SYSTEM INSPECTION
HOME HEATING SAFETY
INDOOR AIR EMERGENCY RESPONSE
Lennox SAFETY WARNING
METAL CHIMNEYS & FLUES
NOISE / SOUND DIAGNOSIS & CURE
ODORS & SMELLS DIAGNOSIS & CURE
ODORS FROM HEATING SYSTEMS
OIL HEAT SAFETY INSPECTIONS
PLASTIC HEATER VENTS
ROOF STAINS from CHIMNEYS
SAFETY RECALLS CHIMNEYS VENTS HEATERS
SHARED CHIMNEY & FLUE HAZARDS
Shared Chimney Flue Examples
Exceptions: Shared Flues Permitted?
Wood & Oil Fired Heaters
Two Gas Fired Appliances Vent in One Flue
Multiple Fireplaces Sharing One Flue
STAIN DIAGNOSIS on BUILDING EXTERIORS
STAINS on/near CHIMNEYS
Three-Sided Chimneys: Problems
TRANSITE PIPE CHIMNEYS & FLUES
UNLINED FLUE INSPECTIONS
WOOD, COAL STOVES & FIREPLACES
This article describes shared chimney flues, multiple heating appliances, fireplaces, woodstoves all using the same chimney venting path through a building and to outside. Shared flues can create fire and smoke spread hazards and carbon monoxide hazards in buildings.
Here we outline how to detect shared chimney flues, how they are repaired, and we list the exceptions to the rule, showing when, in some jurisdictions, it is permitted to vent more than one heating appliance into a single chimney flue and when it is permitted to vent both oil and gas-fired appliances into the same flue.
Our photo (page top) shows three heating appliance, each connected by its own flue vent connector to a masonry block chimney. Is this OK? the answer is, it depends. On the chimney flue size and other installation details. Notice too that we are sharing the flue between oil and wood fired appliances. See Exceptions: Shared Flues Permitted?
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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Fire spread and combustion gas or carbon monoxide hazards: gases may be conducted from a heating appliance to another area in the building when the flue divider is missing.
For example, dangerous carbon monoxide from a basement gas fired heater or a coal stove may leak into an upper building floor through a fireplace or woodstove connected to the same flue.
As Carson Dunlop's sketch points out (above left), the missing divider from the chimney shown in our photo above and in the sketch at left may permit dangerous flue gases or carbon monoxide to enter the living area through a fireplace. Proper construction of chimney walls in a modern masonry flue is shown at above right.
Our photo (above/left) shows that the clay flue tiles are just 1.5" apart (left flue pair) and about 2" apart (right flue pair) - too close according to the sketch above.
This is especially the case if elsewhere in the building a gas (or oil) fired heater is using the same chimney.
It was common for chimney flues to be shared in older buildings in the following ways (and probably others you can suggest to us). All of the examples in the following list are unsafe and should be corrected immediately.
Shared Flue Vent Connector and Chimney - Soot Blow-back Clue
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Technical Reviewers & References
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