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Metal chimneys & flues for fireplaces:
This article explains the use, requirements, installation and inspection of triple wall metal chimneys used for fireplace inserts and zero-clearance fireplaces.
This article series on chimneys, chimney construction, 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.
Triple walled metal chimneys such as shown in Carson Dunlop's sketches are often used to vent "Zero-clearance" fireplace inserts.
The sketch above shows that the metal chimney may be permitted to run at angle of up to 60 deg. in some jurisdictions. If the angled chimney is constructed of masonry, such as a chimney lined with clay chimney tiles, see Mitering Angled Chimney Flues for notes on proper mitering of the flue liner tiles and other angled or sloped chimney concerns.
Fireplace inserts often are provided with steel spacers to force the installer to provide safe clearance from nearby wood framing or other combustibles.
As the sketch explains, an air-cooled or air-insulated triple wall chimney of this type is used only for zero-clearance fireplaces. If used to vent a wood stove the chimney is likely to be too cool, leading to a dangerous creosote build-up - a source of potentially fatal chimney fires.
"Zero Clearance" fireplaces and vents are usually not rated for literally zero clearance from combustibles, or greater fire clearance distances may be required by local or national fire safety codes.
If a homeowner converts a zero-clearance fireplace to a wood-stove hook-up the installation that uses a triple-wall metal chimney the installation is likely to be improper and dangerous.
Also remember to inspect zero-clearance fireplace installations to be sure that the clearance-projections are intact. We've found them hammered flat to cram a fireplace insert into a location where it did not fit - and was unsafe. Peer into cavities that vent room air around the fireplace or into openings around the fireplace to look at fire clearances wherever possible, or if in doubt, it may be necessary to cut an inspection opening into the adjoining wall.
This level of invasive inspection is a normal home inspection procedure but might be recommended as a further step in some circumstances such as where an installation was not inspected or where it has been performed by un-trained personnel.
Metal & Factory-Built Fireplace Chimney Inspection Checklist
Common Factory-Built Fireplace Metal Chimney Defects, Problems, Unsafe Conditions
Chimney Installation: all parts of a factory-built fireplace or chimney must be installed according to instructions provided by the manufacturer and no parts can be damaged to an extent that would impair the function of that part.
Chimney Labels: all parts of a factory-built fireplace or chimney system (except in some jursidictions locally-made covers) must bear labels identifying the parts as listed for use with the fireplace model installed in the building. Examples of labeling issues and even counterfeit labels are at CHIMNEY SHROUD, Decorative
Fireplace chimney & Chimney connections: the chimney should be inspected for proper construction, safe operating condition, etc. as appropriate for the type of chimney materials and construction (masonry, factory-built, etc).
Required combustible clearances: the manufacturer-specified air space or clearance must be provided between the chimney exterior surfaces and all combustible materials or building insulation. Clearances and installation must also comply with information provided by the chimney manufacturer's instructions and labels.
Chimney top height clearance: the chimney height above roof must be at least three feet above the roof surface (measured on the up-slope-roof side of the chimney) and at least two feet above any building compnent or structure found within ten feet of horizontal distance.
Chimney chase, housing, surrounding stucture: shall be constructed using materials, clearances, and sealing/flashing/fire-stops as specified by the chimney manufacturer and local building codes.
Where the factory-built fireplace chimney passes through living spaces of the building interior it must be enclosed and have proper fire-stops installed at ceilings or floors as specified by the manufactuer or local building codes.
Chimney angles, slope, elbows: the chimney should not slope less than 30 degrees or less as required by the manufacturer or local building codes; (Some local codes require steeper angles). Sections of chimney above any elbows must be supported by straps or other mounts specified by the manufacturer or local codes sufficient to carry the weight of the chimney above.
The fireplace owners manual and operating instructions should be provided and should be placed where readily accessible to building occupants. The fireplace identifying tags such as serial number and model number and UL listing or other listing certifications and labels provided by the manufacturer should be intact and left in place as originally installed by the manufacturer.
Inspection checklist warning: No checklist is ever a complete guide to building inspection or diagnosis since no checklist can contain every possible hazard or every clue that suggests a problem.
Therefore do not rely on this or any checklist to assure that your inspection of a chimney is complete. Instead, use this list to suggest additional topics that you otherwise may have omitted from your inspection. The more detailed chimney inspection and repair articles at the links at Related Links and the citations below below suggest further, more-detailed chimney inspection points and procedures.
Adapted from chimney inspection safety sources including these documents cited at REFERENCES
 Baird, David J., C.B.O., "Factory-built Chimney Chase Fires: A case for More Detailed Inspection", Building Standards, March-April 1991, pp. 14-17.
 Purdie, Roger K., "Chimney Fire Safety Bulletin", Vista Fire Protection District, 2001, report of house fire related to the home's metal chimney. Contains advice for chimney * fire safety & sketches of approved and not-code-approved metal chimney tops, caps & crowns. [PDF]
 Fire Inspector Guidebook, [BOOK] 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.
 "Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
 "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.
 "Chimney Inspection Procedures & Codes," Donald V. Cohen, draft, was to be published in the first volume of the 1994 ASHI Technical Journal by D. Friedman
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(June 18, 2014) Morgan said:
Does the outer walls of the triple walled chimney also act as a fresh air intake? I have a zero clearance fireplace on an interior wall and my home was recently inspected and the inspector stated that it needs a fresh air intake, any help in with this matter would be greatly appreciated.
Not quite, Morgan. Click to enlarge our page top photo and you'll see that indeed air does flow both up and down between concentric walls of a triple walled chimney, but that airflow is intended to cool rhe chimney. Interfering with that airflow, for example by diverting it for combustion use risks overheating the chimney, at least in the design we illustrate.
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Questions & answers or comments about metal chimneys used with fireplace inserts and zero-clearance fireplaces: installation, inspection, diagnosis, repair, & specifications or codes.
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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: email@example.com
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 firstname.lastname@example.org
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: email@example.com. 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