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-Wall Metal Chimneys for Fireplaces

Triple walled metal chimneys such as shown in Carson Dunlop Associates [at REVIEWERS] sketches are often used to vent "Zero-clearance" fireplace inserts.

This article gives detailed Inspection points and a photo guide to triple-wall metal or fireplace chimney defects & inspection procedures.

We include a CHECKLIST for metal fireplace chimney inspection

The sketch below 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 ANGLED CHIMNEYS 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

Notes to the table 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 atReferences or Citations

• [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", [PDF] 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, [Website] 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: CHIMNEY INSPECTION DIAGNOSIS REPAIR. 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, [Book at Amazon] American Society of Civil Engineers, 2003

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-08-02 by Mike

I have a triple-wall chimney in the interior wall of my condominium, between two units, built in 1993. I am a new owner of the condo.

A recent inspection suggests the metal chimney does not have enough clearance from the surrounding wood framing. Yet, it has been in use for 27 years. Why would it be a problem now? (gas burning fireplace)

Another condo owner in same complex has suggested the nature of the triple walls of the metal chimney prevent the outer wall from getting too hot and it should not be a problem.

Should I be concerned? Can I continue to use the gas burning fireplace / chimney without modification? Picture attached.

On 2019-02-14 - by (mod) -

If you meet the fire clearance distance requirements

On 2019-02-14 by bevm

I would like to install a zero clearance fireplace in a great room.

I will follow the manufacturer specified recommendations on the required height of the fireplace enclosure-- actually exceeding the height requirement by 2+ feet. Would I be able to leave the chimney area exposed above the required enclosure to the height of the cathedral ceiling?

There are no floors around the chimney in this location where the pipe can be touched or bumped.

The installation manual states the "chimney must be totally enclosed when passing through a living space with a minimum 2" clearance to combustibles."

It does not pass through a second floor so does the chimney in this are need to be enclosed by a chase? There would be firestops at both the exit from the fireplace enclosure and at the ceiling. I have included an image for your review. Thanks.
IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2017-12-20 - by (mod) -

Ken

Chimney Cleaning Frequency

Sorry but in my view there is not one single "right" answer. The chimney needs to be cleaned when it's dirty or has built up deposits of soot and creosote. The rate of deposits in a chimney depends on

- the thickness of creosote & soot on the flue interior (1/4" to 1/8" = ready for cleaning, 1/8" or more, clean immediately, unsafe)

- the frequency and duration of fireplace use

- the temperature of fireplace operation (higher temps, less creosote, slower deposition)

- the quality of firewood (green, more-sap, much higher rate of creosote formation)

- the specific chimney height and draft (that also affects condensation in the flue and creosote formation)

It would be reasonable to say an annual inspection and clean-out if needed would be the minimum safe procedure.

Or you can inspect the flue interior - taking care not to get soot in your eye - by scratching the deposits you can see to estimate the thickness of the soot and creosote layer.

See also CHIMNEY CLEANING PROCEDURE https://inspectapedia.com/chimneys/Chimney_Cleaning_Procedures.php

On 2017-12-20 by Ken

How often should a triple wall zero clearance fireplace be cleaned by a chimney sweep?

On 2017-02-18 - by (mod) -

Probably; your building department will need to approve the modification - at least in most jurisdictions. Check also with the manufacturer about the contact of the metal chimney with the existing chimney wall.

On 2017-02-16 by tim

can I install a triple wall vent pipe inside my chimney which vents my oil furnace? there will be zero clearance on one side and about 3 inches on the other. the pipe is round and the chimney is 8in by 11 in a rectangle.

On 2016-11-27 - by (mod) -

Richard,

Using any chimney for sixteen years without a cleaning or inspection is risking a house fire and death of the occupants. That is more true for a wood-burning chimney where creosote accumulation is likely.

I inspected a house fire at which occupants had felt that their woodstove chimney had worked "just fine for years". They left the home in charge of a house sitter who built a nice hot fire in the family room woodstove- it was cold outside. She got just one fire. It consumed the house.

On 2016-11-27 by Richard

I have an insert with a triple wall pipe running from the stove in a straight line up through the roof. I have used the "cleaning" logs but have never actually cleaned it. After 16 years it's still working great? Should I have it cleaned?

On 2015-07-04 by gail

I seem to have soot (light flakes - not creosote) accumulating inside the cavity of a double-wall vent pipe. This is a 3' section above the roof, with single-wall on the interior. There is a transition box between the two. I think it's Duravent. I have a proper (same manufacturer) cap. When I clean the stovepipe, I can see the openings into the triple-wall. Is that usual? Since this is a flammable material, how do I get it out (vacuum from top when cleaning the chimney?) And more importantly, how to I prevent this in the future? Don't tell me to call a sweep. If you don't know, just say so.

Question:

(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.

Reply:

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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Continue reading at FIRE CLEARANCES INDOORS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CHIMNEY HEIGHT & CLEARANCE CODE
• FIRE CLEARANCES INDOORS
• FIRE CLEARANCES, METAL CHIMNEYS
• FIREPLACES & HEARTHS/A> - home
  • FIREPLACE CHIMNEY ROOF CLEARANCE
  • FIREPLACE & WOODSTOVE CONTAMINANTS
  • FIREPLACE INSERTS INSTALL, INSPECT, REPAIR
  • FIREPLACE INSPECTION PRE-FAB
  • FIREPLACE INSPECTIONS
  • FIREPLACE DAMPERS
  • GAS FIREPLACES & GAS LOGS
• METAL CHIMNEYS & FLUES - home
• METAL CHIMNEY INSTALLATION MANUALS

Suggested citation for this web page

TRIPLE-WALL METAL FIREPLACE CHIMNEYS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE INDEX to CHIMNEYS & FLUES

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Citations & References

In addition to any citations in the article above, a full list is available on request.

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