DEAD END CHIMNEY FLUE HAZARDS - CONTENTS: What is a dead end flue or dead base chimney flue. Warnings about unsafe blocked chimney flues. Heating system & chimney service, maintenance & inspection suggestions for dead end chimneys & flues. Solutions for the Dead End Chimney or Dead Base Flue Problem.
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Definition & hazards of dead end chimneys & flues.
This article describes dead base or dead end flues and explains why they can cause heating equipment operating difficulties or why they may be unsafe. A dead end flue is one in which the flue vent connector joins at the very base of a chimney.
Debris falling down the chimney can quickly block the flue, prevent proper removal of exhaust gases from the building heating equipment, and can be dangerous. We describe how to spot dead end chimneys, how to recognize trouble signs, and what to do about dead end chimney venting systems.
Dead-end flues, chimneys whose flue stops right at the point of entry of a thimble
for a woodstove or heating appliance are inherently more dangerous than a conventional flue
which extends several feet further past the thimble. Dead end flues are quickly and easily
blocked by any debris that might fall down a chimney.
[Click to enlarge any image]
If a chimneys venting a gas-fired appliance
becomes partly or totally blocked, the appliance is likely to rapidly produce very dangerous,
potentially fatal carbon monoxide (CO).
Be sure that chimneys of this type are inspected and
cleaned annually and be sure that you have working CO detectors as well as smoke detectors in
The dead end flue in this photo (above) can be determined because we're venting that long run from a heating boiler into the bottom of a chimney that's just above ground level in a crawl space. Looks as if we've got some asbestos paper wrapping the flue - another matter to be addressed.
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.
Dead End Chimney Flue Clues & Examples
Absence of a chimney cleanout - the chimney may stop right where the flue vent connector enters the chimney.
Combustion chamber backpressure burns on the heating equipment (photo at left) may indicate that the chimney is blocked (or there are other draft problems such as an open chimney cleanout door)
Old houses built on stone foundations with no original central heating.
Often when a basement was later excavated or deepened to install a heating boiler or furnace, the only connection into a chimney flue was an entry point at or close to ground level above the basement because the original chimney flue did not extend below ground level.
Look for a chimney that sits atop a stone foundation.
Flue vent connectors (stack pipes or smoke pipes) routed through crawl spaces often enter the bottom of a chimney flue. (Photos above on this page).
Masonry fragments in the cleanout: if you open a chimney cleanout-door or pull the flue vent connector
from a dead end chimney flue, in either case you are looking at the very bottom of the chimney
If you are inspecting a masonry chimney, be alert for discovery of masonry fragments when
inspecting or cleaning the bottom of the flue. If a piece of brick, masonry block, concrete,
or clay flue tile liner is pulled out of your chimney, ask "where do you suppose this came from?"
If the masonry scrap fell during construction of the chimney it may mean nothing.
But if it
fell because the chimney has been damaged, perhaps by water, frost, or during cleaning, then
you probably have an unsafe chimney flue - more investigation is in order, promptly.
you believe that the masonry scrap found at the bottom of a flue fell during original construction,
and if you remove it during cleaning, you should never find another piece in the flue bottom.
If you do, the flue has been damaged anew and it is unsafe.
Chimney use history: if a chimney has been used for a variety fuels, coal, oil, wood, there may be a greater accumulation of debris at the chimney bottom, a mixture of creosote, soot, or even masonry fragments from a flue damaged by corrosive gases and condensate in the flue.
Our photo (left) shows a truly abandoned dead end flue chimney. We changed this building to a direct-vent heating boiler and abandoned the chimney entirely rather than continue to face chimney blockage problems.
Chimney draft problems: if someone has installed a draft inducer fan because they couldn't get enough draft, the problem could be a blocked flue. Look for back-pressure burns on the combustion chamber. Look for a defeated or sealed-up barometric damper. See details at DRAFT REGULATOR, DAMPER, BOOSTER.
Chimney leak history: leak stains inside the building attic or on any floor, if they
are traceable to leaks at a chimney, are reason to be concerned for possible water damage to the
chimney as well as to the building. Further investigation may be warranted.
Chimney cap history: if a chimney has spent part of its life with no cap installed,
there is extra risk of water damage to the flue interior. In a masonry chimney damage may appear
as frost cracking of the upper flue liners or masonry. In any chimney, there may also be
water damage to the heating appliances being vented by that chimney.
Dead end chimney flues are likely to lead to the rusted-out flue vent connector such as we show here.
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.
Experienced heating service technicians are expected to be well aware of the hazards of dead base chimneys & flues, and as our client points out in our photograph (left), the service tech may leave a note to tip off the technician who arrives for the next service call.
To the heating service tech a dead base chimney means
Watch out for blockage at the chimney - be sure to open and clean it out
Watch out for draft problems on the heating equipment
At below left we illustrate another clue that may indicate a dead base chimney - no visible cleanout door below the chimney thimble where the flue vent connector attaches to the flue, and water leak stains directly below the thimble.
Watch out: At above right we illustrate another scary problem often found in deep, hard to access crawl areas: a dead base chimney and a fallen-off or disconnected flue vent connector or "flue pipe" - presenting a fire hazard, a flue gas poisoning hazard, improper heating operation, generally an unsafe heating system.
Why would this problem be more likely here? Because the connection of the flue vent connector to the dead base chimney is deep into a hard-to-access crawl space where nobody wants to go. Be sure to inspect such locations with care.
Solutions for the Dead End Chimney or Dead Base Flue Problem
Safe chimney maintenance: regular annual maintenance must include opening and cleaning the chimney base as well as checking/cleaning the flue vent connector where a dead end flue chimney is in use. Also monitor heating equipment operation for signs of blocked flue passages such as indications of inadequate chimney draft.
Relocate the flue vent connector connection point to higher on the chimney: Where feasible, move the flue vent connector to a higher entry entry point in the chimney, replacing the original dead base entry point with a chimney cleanout door. This option will rarely be feasible or no one in their right mind would have connected the heater to the chimney bottom in the first place.
Eliminate use of the dead base chimney entirely by converting the heating equipment's venting system to a direct through wall power vent system. See our photo at left and for details of this approach see DIRECT VENTS / SIDE WALL VENTS.
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Questions & answers or comments about the inspection procedure & hazards of dead end chimneys & flues.
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Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: firstname.lastname@example.org
Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
Arlene Puentes, an ASHI member and a licensed home inspector in Kingston, NY, and has served on ASHI national committees as well as HVASHI Chapter President. Ms. Puentes can be contacted at email@example.com
Roger Hankeyis principal of Hankey and Brown home inspectors, Eden Prairie, MN, technical review by Roger Hankey, prior chairman, Standards Committee, American Society of Home Inspectors - ASHI. 952 829-0044 - hankeyandbrown.com
NFPA #211-3.1 1988 -
Specific to chimneys, fireplaces, vents and solid fuel burning appliances.
NFPA # 54-7.1 1992 -
Specific to venting of equipment with fan-assisted combustion systems.
Gas Appliance Manufacturers' Association has prepared venting tables for
Category I draft hood equipped central furnaces as well as fan-assisted
combustion system central furnaces.
National Fuel Gas Code, an American National Standard, 4th ed. 1988 (newer edition is available) Secretariats, American Gas Association (AGA), 1515 Wilson Blvd., Arlington VA22209, and National Fire Protection Association (NFPA), Batterymarch Park, Quincy MA 02269. ANSI Z223.1-1988 - NFPA 54-1988. WARNING: be sure to check clearances and other safety guidelines in the latest edition of these standards.
Fire Inspector Guidebook, A Correlation of Fire Safety Requirements Contained in the 1987 BOCA National Codes, (newer edition available), Building Officials and Code Administrators International, Inc. (BOCA), Country Club HIlls, IL 60478 312-799-2300 4th ed. Note: this document is reissued every four years. Be sure to obtain the latest edition.
Uniform Mechanical Code - UMC 1991, Sec 913 (a.) Masonry Chimneys,
refers to Chapters 23, 29, and 37 of the Building Code.
New York 1984 Uniform Fire
Prevention and Building Code, Article 10, Heating, Ventilating, and Air Conditioning Requirements
New York 1979 Uniform Fire Prevention & Building Code, The "requirement" for 8" of solid masonry OR for use of a
flue liner was listed in the One and Two Family Dwelling Code for New
York, in 1979, in Chapter 9, Chimneys and Fireplaces, New York 1979
Building and Fire Prevention Code:
"Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
"Rooftop View Turns to Darkness," Martine Costello, Josh Kovner, New Haven Register, 12 May 1992 p. 11: Catherine Murphy was sunning on a building roof when a chimney collapsed; she fell into and was trapped inside the chimney until rescued by emergency workers.
"Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
"Chimney Inspection Procedures & Codes," Donald V. Cohen was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman, then editor/publisher of that publication. The production of the ASHI Technical Journal and future editions was cancelled by ASHI President Patrick Porzio. Some of the content of Mr. Cohen's original submission has been included in this more complete chimney inspection article: InspectAPedia.com/chimneys/Chimney_Inspection_Repair.php. Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
Natural Gas Weekly Update: http://tonto.eia.doe.gov/oog/info/ngw/ngupdate.asp Official Energy Statistics from the U.S. Government
US Energy Administration: Electrical Energy Costs http://www.eia.doe.gov/fuelelectric.html
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Ceramic Roofware, Hans Van Lemmen, Shire Library, 2008, ISBN-13: 978-0747805694 - Brick chimneys, chimney-pots and roof and ridge tiles have been a feature of the roofs of a wide range of buildings since the late Middle Ages. In the first instance this ceramic roofware was functional - to make the roof weatherproof and to provide an outlet for smoke - but it could also be very decorative.
The practical and ornamental aspects of ceramic roofware can still be seen throughout Britain, particularly on buildings of the Victorian and Edwardian periods. Not only do these often have ornate chimneys and roof tiles but they may also feature ornamental sculptures or highly decorative gable ends. This book charts the history of ceramic roofware from the Middle Ages to the present day, highlighting both practical and decorative applications, and giving information about manufacturers and on the styles and techniques of production and decoration.
Hans van Lemmen is an established author on the history of tiles and has lectured on the subject in Britain and elsewhere. He is founder member and presently publications editor of the British Tiles and Architectural Ceramics Society. Available at the InspectAPedia Bookstore.
Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003 - These guidelines address the inspection of chimneys and stacks. Each guideline assists owners in determining what level of inspection is appropriate to a particular chimney and provides common criteria so that all parties involved have a clear understanding of the scope of the inspection and the end product required. Each chimney or stack is a unique structure, subject to both aggressive operating and natural environments, and degradation over time. Such degradation may be managed via a prudent inspection program followed by maintenance work on any equipment or structure determined to be in need of attention. Sample inspection report specifications, sample field inspection data forms, and an example of a developed plan of a concrete chimney are included in the guidelines. This book provides a valuable guidance tool for chimney and stack inspections and also offers a set of references for these particular inspections.
NFPA 211 - 3-4 - Clearance from Combustible Material
NFPA 54 - 7-1 - Venting of Equipment into chimneys
Brick Institute of America - Flashing Chimneys
Brick Institute of America - Proper Chimney Crowns
Brick Institute of America - Moisture Resistance of Brick
American Gas Association - New Vent Sizing Tables
Chimney Safety Institute of America - Chimney Fires: Causes, Effects, Evaluation
National Chimney Sweep Guild - Yellow Pages of Suppliers
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: firstname.lastname@example.org. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones