Metalbestos or Class A Chimney Installation & Inspection:

This article describes how to select, install, and inspect Class-A insulated metal chimneys such as the Insulated Double Wall MetalBestos™ manufactured metal chimney, also called a zero clearance chimney.

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.

Class A Chimneys - Insulated Double Wall MetalBestos™ type

Watch out: Improper metal chimney installatios are likely to be unsafe.

As you can see from our page top photo, even this superb product can be reduced to shambles when installed by an idiot. The chimney in this photo was not supported, is falling and is unsafe.

See CHIMNEY COLLAPSE RISKS, REPAIRS.

This unfortunate collapsing Class-A type metal chimney was the replacement for the abandoned masonry chimney under the corrugated metal roof we show

at ABANDONED CHIMNEYS, OUTDOORS

and that whose remains we showed

at ABANDONED CHIMNEYS. It looks as if more than one generation of inexpert chimney installers worked in Dover, NY.

Our photo above shows an end view of a section of Metalbestos SS All Fuel Chimney™. The fiberglass insulation is not part of the product and was just left stuffed in that opening.

Class-A Insulated double wall all-fuel chimneys such as the MetalBestos model SS All-Fuel Chimney™ are constructed of double walled stainless steel (usually) and include an insulating material (originally asbestos) between the two metal layers. Class A chimneys have been replaced in some jurisdictions with Super Chimneys

or SUPER CHIMNEYS, 629 CHIMNEYS (also called Type 650 C chimneys) which we discuss below.

Carson Dunlop Associates [at REVIEWERS] sketch at left shows a Class "A" chimney, of which our photos are an example.

Metalbestos™ type chimneys are available in different diameters, lengths, and with elbows, caps, and supporting base kits. These chimneys are used often to vent oil fired heating equipment as well as woodstoves and zero-clearance or built-in fireplaces. Our photograph at above left shows an installation leaving the insulated metal chimney exposed on the home exterior.

While these insulated chimneys may be rated for zero clearance from combustibles by the manufacturer, many building codes require at least a one-inch clearance between the chimney and any combustible materials.

Our photo at CHIMNEY CHASE CONSTRUCTION hows a wood-framed chimney chase that might enclose an insulated metal chimney or a Type-B Gas vent chimney.

Class A Chimney Height Requirements

Complete details about chimney height requirements on buildings including Class A Chimneys are now located

at CHIMNEY HEIGHT & CLEARANCE CODE

Class A Chimney Fire Clearance Details

Complete details about Class-A chimney fire clearances indoors can now be read

at FIRE CLEARANCES, METAL CHIMNEYS

And below on this page see

CLASS A CHIMNEY CODES, STANDARDS & MANUALS

Should an Insulated or "Air Cooled" Metal Chimney Be Replaced After a Chimney Fire has Occurred?

What Kind of Inspection Is Required After a Metal Chimney Fire?

I was looking for information on chimney fires, specifically, on how to inspect double wall pipe after such an event.

The outside of the outer pipe had paper stickers on it that were not burnt or discolored, so I am assuming the pipe did its job. However the top of the chimney run did catch on fire, presumably from the heat generated from the chimney fire. Anyway, I was looking for a category on how to inspect double wall pipe after a fire. - K.M.

Reply: Inspect for visible flue damage, color changes, movement, cracks; but to be safe: in our opinion you should replace the chimney

After a chimney fire (such as from igniting creosote in a metal flue), a competent onsite chimney inspection by an expert usually finds additional clues that help accurately diagnose a problem. That said, we add the following opinion:

In sum: in our opinion after a chimney fire in an insulated metal chimney or an air-insulated metal chimney the chimney should be replaced entirely in order to be safe and to assure that maximum fire protection for the building is maintained. In addition you should inspect for heat or fire damage to surrounding building components. Details follow.

Some chimney repair companies and building codes cite that "metal chimneys must be inspected after a fire for possible need for replacement". We speculate that the chimney inspector will look for deformed, cracked, metal components, movement, color changes in the stainless steel, or signs of overheating or damage to surrounding building components.

If the metal chimney liner and metal exterior of a multi-wall insulated metal chimney are undamaged, one might think that the internal chimney insulation of a multi-wall insulated metal chimney or flue was intact. But that may not be true. In addition there may be subtle damage to surrounding building components such as pyrolysis that could lower the combustion point and increase the risk of a future fire in nearby wood materials.

See FIRE STOPPING in BUILDINGS

Some sources point out that

Stainless Steel turns blue at 900 degrees causing the chemical makeup of chromium carbide to migrate. After this, the stainless steel will rust and cause corrosion. Stainless Steel really should be replaced after chimney fires over 900 degrees. -References or Citations

We have observed steel flues that turned blue and also black after a fire.

A "be safe" approach requires that insulated chimneys are replaced after a fire.

We believe that this makes sense because because during a chimney fire the internal temperatures can be extremely high and thus can damage the flue in both obvious and less obvious ways that may not be visible and no one wants to take a chance.

Furthermore, the "after 900 degrees" rule is impractical: - who is actually measuring chimney temperature during a fire? The 900 deg F number in our OPINION is not helpful.

Most chimney sources point out that it's common for a chimney fire to reach 2000 deg F! Who wants to risk an unsafe flue after a fire when a new fire could still occur and could meet less protection.

A similar example is with earthquake-resistant construction: the construction is designed to keep the building from collapsing and killing the occupants, but it is not expected to prevent any damage whatsoever to the building. So after a quake repairs are going to be needed.

...

Class A Insulated Metal Chimney Manuals, Codes, Safety References

• 2006 ICC MECHANICAL CODE, CHAPTER 8, CHIMNEYS and VENTS [PDF], International Mechanical Code as adopted by Virginia, retrieved 2018/02/12 original source: https://www2.iccsafe.org/states/Virginia/Mechanical/PDFs/Chapter%208_Chimneys%20and%20Vents.pdf
• BRITISH STANDARD BS 5440 CHIMNEY INSTALLATION CLEARANCES MAINTENANCE [PDF] (2000) Installation and maintenance of flues and ventilation for gas appliances of rated input not exceeding 70 kW net (1st, 2nd and
  3rd family gases) — Part 1: Specification for installation and maintenance of flues
• CHIMNEY CODES & STANDARDS - complete list of Chimney & Vent codes & standards
• Dura-Vent Chimney Installation Instructions for the company's various models can be found at https://duravent.com/installation-instructions/ (2021/05/19), including the company's products listed below. Note that a number of these (like the DuraVent DirectVentPro are NOT intended for wood burning or other heating appliances that require use of a multi-walled insulated metal chimney.
  
  CVS® DirectVent® Pro, DuraBlack®, DuraChimney® II, DuraFlex® Aluminum, DuraFlex® Stainless Steel, DuraLiner®, DuraPlus®, DuraSeal®, DuraStack®, DuraStack® Pro, DuraTech® 5"-8", DuraTech® 10"-24", DuraTech® Canada, DuraTech® Premium, DVL®, FasNSeal®, FasNSeal® 80/90, FasNSeal® Flex, FasNSeal® W2, PelletVent® for Multi-Fuel, PelletVent Pro®, PolyPro®, PolyPro® Flex, Type B Gas Vent, Ventinox®
• DuraVent, DURACHIMNEY® INSTALLATION INSTRUCTIONS [PDF] Air-Cooled, All-Fuel Chimney for Fireplaces, DuraVent Co., Tel: : 800-835-4429 Website: www.duravent.com
  
• GAMA, VENTING TABLES, CATGORY I CENTRAL FURNACES [PDF] (1990 & 2000) Gas Appliance Manufacturers' Association,, includes also fan-assisted combustion system central furnaces.
  
  SPECIAL METAL-FAB UPDATE AS OF MARCH 2000 The venting tables within this booklet have now been included in the National Fuel Gas Code (NFPA 54/ANSI Z223.1-1999). That code may also be used to size venting systems for drafthood equipped central furnaces or for fan-assisted combustion system central furnaces.
  
  This booklet contains new venting tables designed specifically for use with Category I central furnaces.
  
  These tables are unique, in that, industry wide venting tables now exist for fan-assisted combustion system central furnaces. Venting tables for these types of appliances are not contained in the National Fuel Gas Code (NFPA 54/ANSI Z223.1-1988).
  
  All requirements contained in this booklet apply to both Category I drafthood equipped central furnaces as well as fan-assisted combustion system central furnaces. At no time should a venting system for a listed Category II, III, or IV central furnace be sized with these tables.
  
  The National Fuel Gas Code (NFPA 54/ANSI Z223.1-1988) may also be used to size venting systems for drafthood equipped central furnaces.
  
  However, at this time, the National Fuel Gas Code does not include alternate sizing methods for fan-assisted combustion systems.
  
  Therefore, until engineering data is developed to allow alternate sizing methods for Category I fanassisted central furnaces, the enclosed venting tables must be used for fan-assisted combustion system central furnaces.
  
  These tables apply to venting single appliances and common venting multiple appliances in both metal and masonry chimneys.
• ICC Chimneys, Excel FACTORY BUILT CHIMNEY INSTALLATION & MAINTENANCE INSTRUCTIONS [PDF]Industrial Chimney Company 400, boulevard J-F Kennedy St-Jérome (Québec) Canada, J7Y 4B7 T. (450) 565-6336 Wrbsite: icc-rsf.com retrieved 2020/02/21 original source: https://icc-chimney.com/c/icc/file_db/docs_document.file_en/XLUSA-II_2012-01.pdf
• Metal-Fab TEMP/GUARD CHIMNEY INSTALLATION & MAINTENANCE INSTRUCTIONS [PDF] Metal-Fab Inc., 3025 May Street Wichita, Kansas 67213 USA, Tel: 1-800-835-2830 FAX: 316-943-2717 Email: info@mtlfab.com Website: https://www.mtlfab.com/ retrieved 2020/02/21 original source: https://www.mtlfab.com/media/TempGuard_All-Fuel_Chimney_Instructions_6-12_USA-L944.pdf
• 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.
• ICC, Fire Inspector Guide Based on the 2021 International Fire Code [ICC Digital Subscription] International Code Council
• Hart & Cooley, CHIMNEY RAIN CAP, FLASHING, STORM COLLAR, SPARK ARRESTER INSTALLATION INSTRUCTIONS [PDF] (2013) - retrieved 2022/06/15, original source: https://www.ameri-vent.com/assets/files/15h/8513591.pdf
• NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, (2024) at the NFPA Bookstore, (Older NFPA 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.
• Selkirk, S-3 METAL CHIMNEY CAP, FLASHING, STORM COLLAR INSTALLATION INSTRUCTIONS [PDF] Selkirk, 5030 Corporate Exchange Blvd. SE, Grand Rapids, MI 49512 USA, Tel: 1-800-992-VENT (8368), - retrieved 2022/06/15, original source: https://www.selkirkcorp.com/literature/S3_Round_Top _Flashings _Storm_Collar _Spark_Arrester_and_Roof_Brace_Kit.pdf
• SUPER VENT 2100 & SUPER PRO 2100 INSTALLATION INSTRUCTIONS & MAINTENANCE GUIDE [PDF] FACTORY-BUILT 650° C INSULATED CHIMNEY GUIDE Tested To
  CAN/ULC-S629 & UL103 Type HT, retrieved 2018/02/12, original source: http://www.selkirkcorp.ca/~/media/selkirk/reference-documents/common/file/installation/chimney/superpro-2100-alt/2100-installation-instructions.pdf
  

  Contact the Selkirk company at 800.992.8368 or by Email: info@selkirkcorp.com Selkirk Corporation, 5030 Corporate Exchange Blvd. SE, Grand Rapids, MI 49512 USA
  or

  Selkirk Canada Corporation, P.O. Box 526, Depot 1, Hamilton, ON L8L 7X6 Tel: 888.SELKIRK (735.5475)

• 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:

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-12-25 - by (mod) -

Yes maybe;

The concern, Tom, is that the 8" chimney may be too cool and too large for a gas-fired water heater to develop sufficient draft; without enough draft such a water heater is unsafe as it risks spilling flue gases and dangerous carbon monoxide into the building interior.

It might be possible to use a power vent or draft booster. Check with the water heater's manufacturer or with the installation manual for your heater brand and model.

Let me know if you have further questions, details, opinions.

On 2020-12-25 by Tom

Can a water heater with a 4" vent be vented into to an existing 8" steel chimney? There are no other structures that would vent into the chimney

On 2020-10-10 - by (mod) -

Gary

Thank you for the interesting fuel conversion chimney question.


I would not change fuels in a chimney without first having the existing flue cleaned of creosote deposits in order to reduce a future fire or corrosion hazard.

At that point if you want to wind the existing chimney with a smaller gas flu that sounds like an interesting possibility. I would not proceed to actually buy the equipment to do that before checking with the manufacturer.

On 2020-10-10 by Gary

I have a class A chimney that I used for a freestanding wood stove. I purcashed a used Osburn free standing natural gas stove and would like to know if I can use the chimney. The Osburn asks for a Simpson Duravent direct vent number DV-GS.

I was thinking of running a 4" chimney up the middle of the class A 6" ,it runs vertical through the center of the house.

So the 4" would vent the waste and the surrounding area would be freach air. Is this possible/?

I talked to a HVAC guy and he didnt think it was a bad idea... but...The class A passed all inspections and I burned wood in it for several years.

Question: ok (safe) to vent a corn furnace (in the basement) with an external steel flue that runs in front of a window

(Sept 17, 2014) Craig Swindell said:
Thank you for posting all this great information!\

(Nov 3, 2014) Anonymous said:
is it ok (safe) to vent a corn furnace (in the basement) with an external steel flue that runs in front of a window on the 1st floor of a home.

Reply: No NFPA 211(2010):8.1.1 does not permit use of single-wall metal chimneys or unlisted metal chimneys inside or outside a one- or two-family dwelling.

(Nov 11, 2014) NH Fire Bear

NFPA 211(2010):8.1.1 does not permit use of single-wall metal chimneys or unlisted metal chimneys inside or outside a one- or two-family dwelling.

Even where permitted, an unshielded metal chimney must be no less than 2 ft from any window, door or walkway. 8.2.2.1.4. Locally adopted or amended codes may differ.

...

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

Or see these

Recommended Articles

• CHIMNEY INSPECTION DIAGNOSIS REPAIR - home
• CHIMNEY DRAFT & PERFORMANCE
• CHIMNEY FIRE ACTION / PREVENTION
• CHIMNEY FLUE INSPECTION CAMERA
• CHIMNEY RE-LINING CHOICES
• CHIMNEY SAFETY, WOOD BURNING - CPSC
• CHIMNEY TYPES & MATERIALS
• CLASS A CHIMNEYS, MetalBestos™
• FIRE CLEARANCES, METAL CHIMNEYS
• FIREPLACE INSERTS INSTALL, INSPECT, REPAIR
• FIREPLACE INSPECTION PRE-FAB
• MANUFACTURED CHIMNEYS - definition
• METAL CHIMNEY FLUE SEPARATION CODES
• METAL CHIMNEYS & FLUES - home

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CLASS A CHIMNEYS, MetalBestos™ 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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