Detailed Inspection & Photo Guide to chimney masonry or clay flue tile damage & defects
Types of damage to masonry chimney liners & flue tiles
What to do about damaged chimney flue tiles
Questions & answers about chimney flue tile inspection, diagnosis, repair
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This article describes how to detect and assess chimney flue tile or flue line damage and how that damage is repaired.
Also see Re-Lining Choices for Masonry Chimneys. 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. As with most inspection and safety topics, this material may be incomplete.
Flue liners can be made of clay, ceramic or metal and must contain the
products of combustion and protect the shell from heat and corrosion. Clay
linings are usually square, round or rectangular sections two feet in length. They
are stacked upon each other with refractory cement in the joints to form a
continuous smooth walled vent from below the appliance inlet to the top. A space
of one half inch to one inch must be maintained between the flue and masonry
surround. Alignment of the flue tiles is secured with one walnut sized mortar
deposit between the masonry surround and each of the faces of the tile.
As the flue is heated the warm liner will expand outward and lengthwise.
Thus it is important that the liner not be secured to the surrounding masonry. The
air space effects a reduction of temperature at the exterior of the masonry
surround and helps to maintain the elevated temperature of the flue for proper
draft.
Damaged clay flue tiles lining a chimney are often obvious only from a rooftop inspection such as we show in these photos. At above left we see that frost has broken off a portion of the clay liner for this chimney and that fine cracks in the clay flue tiles tell us that additional damage may have occurred below.
At above right we see poor chimney construction that left misaligned chimney tiles, inviting water to leak into the chimney structure, adding to the risk of frost damage and possibly causing an unsafe flue.
Damage to clay chimney flue tile liners can also appear as spalling shown in our photo (above left) or as shown in Carson Dunlop's sketch (above right). Notice that the chimney wall is getting thin at the left side of the flue. It is time to have this chimney lined for safety.
Many water damaged chimney flues could have been prevented by installation of a good chimney rain cap and crown or top seal at the time of construction.
The sketch at left shows the effects of gaps in a chimney liner. While the drawing depicts a regular gap as if magically the upper clay flue tile was suspended curing chimney construction, this is not as impossible as it may seem. Details in the drawing show the upper liner was suspended by nails, leaving a mortar gap between the clay flue tiles.
This flue tile liner gap can also occur if sections of the flue tiles are broken and lost after chimney construction, later in its life.
These flue liner gaps may explain why white efflorescence appears mysteriously somewhere below the top of the exterior of a masonry chimney. Gaps in the chimney liner can be found by a camera inspection of the flue interior; they might be suspected based on damage or stains on the chimney exterior.
Significance of Finding Soot at the Chimney Top
Safety Warning: If you see soot forming at a chimney which is venting gas-fired appliances you should shut the equipment down immediately and call for an expert to inspect and correct the chimney or equipment problem. Gas fired equipment can suddenly malfunction, producing soot, and blocking a chimney.
The result is the production of dangerous, possibly fatal carbon monoxide gas. Be sure that your building has working carbon monoxide detectors (CO Gas Detectors) as well as working smoke detectors that are properly located and installed.
Soot at the top of a chimney, regardless of whether the chimney is metal or masonry, can be a clue about improper and inefficient heating system operation where oil-fired heating boilers, furnaces, or water heaters are installed.
Photo of a sooty metal chimney cap venting an oil-fired heater was provided courtesy of Roger Hankey.
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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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