Triple wall metal chimney (C) Carson Dunlop Associates Triple-Wall Metal Chimneys for Fireplaces
Metal fireplace inspection points & checklist

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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.

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Triple-Wall Metal Chimneys for Fireplaces

Triple wall metal chimney (C) Carson Dunlop Associates Angle of offset permitted in a gas vent (C) Carson Dunlop Associates

Triple walled metal chimneys such as shown in Carson Dunlop's sketches are often used to vent "Zero-clearance" fireplace inserts.

The sketch at above right 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

© Copyright 2015, All Rights Reserved. Author Daniel Friedman.

Item # Fireplace Chimney Defect, Concern, Hazard Comment / More Detail

Building ID & Location: __________________________________________

Date & Time: _________________________________________________

Inspector: ____________________________________________________

1 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. FIREPLACE INSERTS
2 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 CHIMNEY INSPECTION CHECKLIST
3 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.

5 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 HEIGHT & CLEARANCE CODE
6 Chimney top cap, shroud, termination: must use listed components, installed & secured according to the manufacturer's instructions & local building codes CHIMNEY CAP & CROWN

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.

8 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. ANGLED Chimneys
9 Chimney damage: the chimney and its supports, cover, or other components must be un-damaged in any way that may interfere with its safe and proper operation  
10 Chimney cleaning: the chimney must not be obstructed by debris, soot, creosote, animal nests etc.



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.

Additional fireplace safety inspection details are provided at FIREPLACES & HEARTHS, at FIREPLACE INSPECTION PRE-FABat FIREPLACE INSERTS and at FIREPLACE INSPECTIONS

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

  • [3] Wood Heating Alliance, "Building Inspector's Checklist for Factory Built Fireplaces" [PDF]
  • [4] 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.
  • [5] 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]
  • [12] 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.
  • [15] "Top Ten Chimney (and related) Problems Encountered by One Chimney Sweep," Hudson Valley ASHI education seminar, 3 January 2000, contributed by Bob Hansen, ASHI
  • [16] Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
  • [18] "Chimneys and Vents," Mark J. Reinmiller, P.E., ASHI Technical Journal, Vol. 1 No. 2 July 1991 p. 34-38.
  • [19] "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: Copies of earlier editions of the ASHI Technical Journal are available from ASHI, the American Society of Home Inspectors.
  • [20] "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
  • [25] Chimney Inspection Checklist, Carson Dunlop, Associates, Toronto, Ontario
  • [26] Chimney & Stack Inspection Guidelines, American Society of Civil Engineers, 2003

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