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This article describes flue vent connectors used to connect heating appliances to a chimney in order to safely deliver combustion gases to a chimney for venting outside the building. Flue vent connectors are not the same thing as a chimney and they have their own safety and installation requirements including slope, materials, diameter, and clearance from combustibles. Readers should also see the fire safety distances required for flue vent connectors at Fire Clearances, Single-Wall Metal Flues. Our photo (page top) shows three heating appliance, each connected by its own flue vent connector to a masonry block chimney. This website provides 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. As with most inspection and safety topics, this material may be incomplete. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. Flue Vent Connectors - Heating Boilers, Furnaces, Water Heaters & Chimney FluesFlue vent connectors for "B" or "L" Vents: A vent connector connects gas equipment to a flue or chimney. Appliances having draft hoods and installed in an attic or concealed space must use Type B or L connectors. Appliances installed in basements can use Type B or Type L or metal pipe (.0304" thick) or aluminum pipe (.012" thick). Gas fired equipment should not be connected to any flue serving solid fuel appliances. Multiple gas vents into a single flue: Where two or more vent connectors enter a common gas vent, chimney flue or single wall metal pipe, the smaller connector shall enter at the highest level consistent with available headroom and clearance to combustibles. Avoid unnecessary bends and secure all joints with sheet metal screws or other approved means. Chimney Blocked at the Flue Vent ConnectorDebris falling down a "dead end flue" easily blocks the flue vent connection and chimney (photo, below right). Carson Dunlop's sketch (below left) shows fallen bricks blocking the bottom of the flue so that even where a "dead end" flue was not constructed - that is, where a chimney cleanout was installed - falling debris can so fill up the chamber at the bottom of the chimney flue that the effect is the same: a blocked chimney flue and the production of carbon monoxide.
A blocked flue case study is reported at UNLINED FLUE INSPECTIONS. Flue Vent Connector Too Far into Chimney
Proper Joint Connections for Single Wall Metal Flue Vent Pipes
It's easy to spot an improperly-joined flue vent connector pair of sections: you will often see stains from leaks oozing out at the section joints. Flue vent connector horizontal length limits
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The maximum horizontal length of vent connectors per the GAMA tables is limited to 1.5 feet per inch of diameter with a provision of a 10% reduction in capacity for each multiple of the length permitted. The venting tables must be consulted to size an adequate venting system. Our photo shows a very long dead flue vent connector joining a heating appliance to a dead end chimney. |
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Carson Dunlop's sketch (above left) shows a loose flue vent connector at the chimney. This is one of the most common chimney and venting defects we observe in buildings.
This defect can often be seen by careful visual inspection of the flue vent connector at the chimney. Our photo (above right) shows our client pointing to a flue vent connector that was not sealed at the chimney thimble.
The results of a loose or leaky vent connection at the chimney include inadequate chimney draft (unsafe heater operation) and leakage of potentially dangerous combustion gases into the building.
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. |
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This flue vent connector (photo at left) has rusted through from water leaking down the chimney into the vent connector elbow. On an oil-fired system we expect soot to blow out of this opening at system startup and during the system run cycle the opening may interfere with proper system draft. The opening leaves a fire risk should a spark blow out of this opening. On a gas-fired system a flue vent connector with a rust hole increases the chance of inadequate draft and dangerous carbon monoxide release in the building. This flue vent connector elbow,rusted through with a large hole, needs to be replaced and more, we need to identify and repair the source of water leakage into the chimney that caused this damage. |
Metal flue vent connectors such as shown in Carson Dunlop's sketch should:
All draft hood vent connectors must slope upward toward the flue connection at 1/4" per foot of length. |
Readers should also see the fire safety distances required for flue vent connectors at Fire Clearances, Single-Wall Metal Flues.
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
CHIMNEY INSPECTION DIAGNOSIS REPAIR
CHIMNEY INSPECTION & REPAIR GUIDE
CHIMNEY INSPECTION DIAGNOSIS REPAIR
Chimneys Cleaning Advice, Procedures
Chimney Cleanout Doors
Chimney Crack & Collapse Risks, Repairs
Chimney Draft & Performance
Chimney Inspection Checklist
Chimney Inspection Indoor Procedures
Attic Chimney Inspection
Chimney Inspection Outdoors From Ground
Chimney Crack Detection & Diagnosis
Chimney Inspection Outdoors From Ground
Chimney Height & Clearance
Chimney Inspection Outdoors at Rooftop
Chimney Cap & Crown Inspection
Chimney Types & Materials
Chimney Cleanout Doors
Fire Clearances for Masonry Chimneys
Fire Clearances for Metal Chimneys
Fire Clearances, Single-Wall Metal Flues
Flue Sizing of Chimneys
Fire Stopping Between Floors
Flue Vent Connectors - Boilers, Furnaces
Blocked Chimney at the Flue Vent Connector
Dead End Chimney Flue Hazards
Extended Too Far into Chimney
Joint Connections - Single Wall Metal Flues
Length Limits for a Flue Vent Connector
Loose, Leaky, Not Sealed, Flue Vent Connector
Plastic Heater Vents
Plastic Vents Goodman HTPV Recall
Rusted Metal Flue Vent Connectors
Slope, Proper Flue Vent Connector
Chimney Inspection: Flue Interiors
Metal Chimneys & Flues
Shared Chimney & Shared Flue Hazards
Fireplace Damage & Unsafe Hearths - Settlement
Moisture Problems Damage Chimneys
Wood Burning Heaters Fireplaces Stoves
Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.
Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
More expert information on this topic
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 The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems |
 Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab |
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Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.
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