Dead End Flues or Dead Base Chimney Flue Hazards
InspectAPedia® -
What is a dead end flue or dead base chimney flue
Warnings about unsafe blocked chimney flues
Questions & answers about dead end chimneys & flues
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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.
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 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.
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 building.
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.
Dead End Chimney Flue Clues
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
flue.
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.
Certainly if
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 REGULATORS, DAMPERS, BOOSTERS.
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.
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Additional technical contributors & reference sources for this article are listed below.
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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 ap@octoberhome.com
Roger Hankey is 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 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
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.
GAMA -
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.htm. 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
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
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 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
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
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