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

  • POST a QUESTION or COMMENT about metal chimneys used with fireplace inserts and zero-clearance fireplaces: installation, inspection, diagnosis, repair, & specifications or codes

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.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Triple-Wall Metal Chimneys for Fireplaces

Triple wall metal chimney (C) Carson Dunlop AssociatesTriple 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.

Angle of offset permitted in a gas vent (C) Carson Dunlop Associates

"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 2017 InspectApedia.com, 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 INSTALL, INSPECT, REPAIR

FIREPLACE INSPECTIONS
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).

METAL CHIMNEYS & FLUES

CHIMNEY INSPECTION CAMERA

CHIMNEY INSPECTION CHECKLIST

CHIMNEY INSPECTION, FLUE INTERIOR

CHIMNEY INSPECTION OUTDOORS

CHIMNEY INSPECTION INDOORS

CHIMNEY SHROUDS

4

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 HEIGHT & CLEARANCE CODE

FIRE CLEARANCES INDOORS
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

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

CHIMNEY SHROUDS
7

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 CHASE
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.

CHIMNEY CLEANING PROCEDURE

CHIMNEY CLEANING FRAUD

CHIMNEY CLEANOUT DOOR

CREOSOTE DEPOSITS, FIRE HAZARD

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

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

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


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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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