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CHIMNEY INSPECTION DIAGNOSIS REPAIR
BACKDRAFTING HEATING EQUIPMENT
CARBON MONOXIDE - CO
CHIMNEY COMPONENT DEFINITIONS
CHIMNEY FIRE ACTION / PREVENTION
COMBUSTION GASES & PARTICLE HAZARDS
COMBUSTION PRODUCTS & IAQ
FLAME COLOR, BLUE vs YELLOW COMBUSTION
HOME HEATING SAFETY
Moisture / Frost Damaged Chimney
ODORS & SMELLS DIAGNOSIS & CURE
Safety Recalls, Chimneys, Vents, Heaters
STAIN DIAGNOSIS on BUILDING EXTERIORS
WOOD, COAL STOVES & FIREPLACES
WOOD STOVE SAFETY
Flue vent connector specifications & fire clearances: 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.
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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. Chimney inspection methods and chimney repair methods are also discussed.
Flue 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.
Debris 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.
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.
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.
Readers should also see the fire safety distances required for flue vent connectors at FIRE CLEARANCES, Single-Wall Metal Flues.
Frequently Asked Questions (FAQs) about flue vent connectors & stackpipes
Question: is there a Simple rule that relates allowable horizontal flue length and flue vent diameter?
What is the maximux allowable horizontal length of a category 1 appliance vent connector in feet for each inch of its diameter. - S.W.
Reply: Not quite so simple, here are the factors that determien allowable horizontal flue length:
From your question, a simple, straight answer on allowable flue length per inch of flue diameter is not quite possible. Take a look at the National Fuel Gas COde NFPA 54, or ANSI Z223.1, for example, Tables G, and you'll see that the tables consider the following factors that set the allowable horizontal flue length or run:
An example (from a 1988 copy of the National Fuel Gas Code):
a 6" diameter Type B double wall connector with a 15' lateral run and a 15' high chimney can vent 198,000 BTUh of capacity.
So a simplistic equation that gives allowable horizontal distance of a flue vent connector or vent expressed in feet per inch of diameter simply would be wrong and potentially unsafe, risking a carbon monoxide or equipment operating problem.
You will want to consult the proper tables either in one of the codes or in the heating equipment manufacturer's equipment installation procedures (the manufacturer would be expected to have the final say).
Questions & answers or comments about metal flue vent connectors or "stackpipes".
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Technical Reviewers & References
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