Water Leak & Frost Damage to Chimneys & Flues
InspectAPedia® -
How water and moisture leak into and damage chimneys and heating appliances.
Chimney inspection, diagnosis, and repair for water or frost damaged chimneys and flues
Questions & answers about how to spot water or frost damage to chimneys & how that chimney damage may be repaired
This article describes water leaks and moisture that damage masonry and metal chimneys and the heating appliances that are connected to them. We list the common sources of water and leaks and we include warnings for inspectors who need to examine equipment as well as the chimney itself when water or moisture leaks are detected.
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Our photo (page top) shows water pouring into a basement, coming out of the chimney cleanout during a heavy rainstorm. Readers of this article should also see Chimney Crack & Collapse Risks, Repairs. 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.
Our photograph at left shows a stunning waterfall flowing out of a "sealed" chimney cleanout in a basement. Lots of roof spillage or surface runoff was entering the base of this chimney.
Moisture is the major cause of chimney corrosion and disintegration in
both masonry and metal chimneys. The flue gases are acidic in nature and if
allowed to condense and saturate the masonry or joints in metal flues the
destructive results will soon be apparent.
Mechanical problems in the
construction or settlement after construction and over firing or flue fires will also
contribute to the problems.
External moisture enters the chimney through cracked caps, porous
masonry, poor mortar joints and improperly designed and installed roof flashings.
Internal moisture (condensation) collects in cracked or separated flue tiles,
blocked flues and chimney caps.
Masonry chimneys subjected to moisture damage can have efflorescent
salt stains, spalled bricks, eroded mortar joints, flaked cracks in the ceramic flue
liner and cracked caps.
Metal components of a vent system can have rust and white acid stains at
joints, corrosion holes along the bottom of horizontal connectors and corroded
chimney cleanout doors at the base of the flue.
Moisture enters a chimney structure from several locations:
Missing chimney cap lets wind blown rain and snow enter the flue
Damaged chimney crown lets water enter the chimney structure
Leaks at the chimney sides let wind-blown rain enter the chimney structure
Leaks at chimney flashing let water enter the chimney structure
Ground and surface runoff or roof spillage by a building often enter the base of a chimney that extends below ground.
Water leaks into a Chimney can Damage the Chimney and the Appliances Connected to It
The result of leaks into a chimney can be unsafe heating equipment as well as costly damage to the chimney, the appliances connected to it, and to the building itself.
Frost or water damage can crack or break a masonry clay chimney tile resulting in fire or flue gas hazards at the building
Broken chimney flue liner parts can obstruct the chimney flue resulting in dangerous, potentially fatal carbon monoxide gas hazards
Water entering the heating appliance such as a furnace, boiler, water heater or woodstove can cause rust damage to the heater components or can damage electrical controls on the appliance, leading to costly repairs
Water entering a wood-framed chimney chase can also invite insects, rot, or mold problems in the building
Water entering a metal chimney or flue can cause corrosion or rust which perforate the chimney or flue vent connector leading to equipment failure, improper operation, and dangerous flue gas leaks in the building. Even a stainless steel manufactured chimney is not immune to rust and corrosion when it faces the combination of water in the flue interior (or between the layers of metal of a multi-wall chimney) and corrosive acids that form as soot and creosote are dissolved by the water in the flue.
Questions & Answers regarding this article
Questions & answers about how to spot water or frost damage to chimneys & how that chimney damage may be repaired.
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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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