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Metal chimney fire clearance codes & specifications: this article describes the basic fire clearance requirements for four types of manufactured metal chimneys: B-vents, L-vents, Class A chimneys, and 650C Chimneys.
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Fire Safety Clearance Required from Combustibles for Metal Chimneys
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.
Adjacent Metal Chimney Separation Requirements
In addition to the requirement for safety fire clearance from rooftops and other building components, separate metal chimneys that are too close to one another may cause damage resulting in poor chimney performance or an unsafe chimney.
Carson Dunlop Associates [at REVIEWERS] sketch at left shows that metal chimneys should be at least 16 inches apart to avoid damage.
Table of Clearances for Listed Flue Vent Connectors for Gas-Fired Heating Appliances
Clearances for Listed Flue Vent Connectors for Gas-Fired Heating Appliances
Minimum Distance from Combustible Materials
Equipment
B-Vents
L-Vents
Single-Wall Metal Pipe
Factory-Built Chimneys
B-Vents: Listed equipment w/ draft hood & equipment listed for use with B-Vents
as listed
as listed
6-inches
as listed
Residential gas boilers/furnaces, gas conversion burner, draft hood
6-inches
6-inches
9-inches
as listed
L-Vents: Residential appliances listed for use with L-Vents
not permitted
as listed
9-inches
as listed
Incinerators - residential
not permitted
9-inches
18-inches
as listed
Listed gas fired toilets
not permitted
as listed
as listed
as listed
Unlisted residential appliances with draft hood
not permitted
6-inches
9-inches
as listed
Residential & low-heat equipment other than items above
not permitted
9-inches
18-inches
as listed
Medium heat equipment
not permitted
not permitted
36-inches
as listed
Notes to the metal chimney fire clearance table above
Watch out: "as listed" where shown in the table above means that the acceptable fire clearance distances for those chimney types must match or comply with the manufacturer's instructions; those clearance spacings are normally found in at least two locations:
The installation instructions for the specific flue vent connector or metal chimney brand and model or product
A stamping or label found right on the metal chimney product itself
We include an example here: the embossed stamping on a Selkirk B-vent for gas appliances that specifies a minimum of 1-inch clearance to combustibles.
Also see the chimney codes listed below.
Key Articles on Chimney, Flue, & Vent Clearances for Fire Safety & Building Code Compliance
IMPORTANT: see FIRE CLEARANCES, SINGLE WALL METAL FLUES & VENTS for the clearance from combustibles required for flue vent connectors (these are not chimneys, but rather the "flue pipe", "smoke pipe", or "stack pipe" that connects a heating appliance to a chimney.
FIRE STOPPING in BUILDINGS - where fire blocking or fire stopping is required to slow the spread of fire or smoke in buildings
METAL CHIMNEYS & FLUES - topic home, for definitions and characteristics of the different types of metal chimneys.
METAL CHIMNEY FLUE SEPARATION CODES - clearances for multiple metal chimney flues passing through a common chimney chase or inside a single masonry chimney
Reader Question: what's the code on distance and clearance for MetalBestos chimneys & vents vs oil storage tanks?
I am installing a pellet boiler and will need a second metal chimney as I am leaving my oil burner as a backup. I live in Maine. The only place I would like the metal asbestos chimney would run 40” away from my oil tank. Do you know what the code is on this? I am having a heck of a time getting any answers regarding this? - R. B. Windham ME 2/27/2014
Reply:
Insulated metal chimneys typically require a one-inch clearance from combustibles.
I think the reason you're not finding an answer to your question is that we're mixing up different constraints and safety concerns:
The required separation or clearance distances for flue vent connectors (generally single-wall uninsulated metal "flue pipes" or "stack pipes" that connect the heater to the chimney) - discussed
at FLUE VENT CONNECTORS, HEATING EQUIPMENT
The required separation of metal or insulated chimneys themselves from various building components or combustibles - discussed
On 2019-10-07 by (mod) - What is the original specification for clearances from the outer wall to combustibles for our fireplace and its chimney?
R Conn
Thanks for a really important metal chimney fire clearance safety question.
In the article above on this page we give typical fire clearance distances for the most-common types of metal flues and chimneys.
Watch out: Beyond that I'm way too chicken to bet your life and money and fire risk on a guessed answer. Instead, let's take a look at the specific metal chimney product you have installed; there will be embossed stampings or data tags on the metal flue product that give its brand and model and clearance minimums.
I don't know what Majestic fireplace model you have installed nor what fuel it's burning nor a thing about the surrounding construction; so the required clearance distances could vary.
Corporate Office
7571 215th Street West
Lakeville, MN 55044
Customer Service:1 (877) 486-9123 retrieved 2019/10/07 original source: https://downloads.hearthnhome.com/installManuals/Ashland%2036_ASH36_Installation%20Manual_4059-909.pdf warns
Comply with all minimum clearances to combustibles as specified. Failure to comply may
cause house fire.
and continues to give clearance distances at 40 spots in the manual .The sketch below is excerpted from that manual.
Below is a similar example showing the data tag on an Ameri-Vent Type B Gas Vent from American Metal Products, manufactured in Mexico and UL Listed.
On 2019-10-06 by R Conn
- clearance distances for our Majestic Fireplace
I have a majestic fireplace installed in our home, I believe it was put in during the early to mid 70’s. It has a 3 wall metal chimney, it is not insulated, but air cooled between the 2’nd and 3’rd structures.
I believe the inside is stainless. The outside is galvanized. It is straight up a chimney chase inside the home. There is an insulated attic above the fireplace where the chimney penetrates then up through the roof with another roof mounted chase.
It appears to be in excellent condition. I’m having the home re-insulated, with high density cellulose.
It appears the original installation allows about 1.5” if clearance in a framed pass through the ceiling, in other words the current fiberglass insulation is about 1.5” away, leaving the lower chimney chase able to breath or release heat.
However it also allows cold air into that chamber during the winter, and we can feel the chase is very cold. It is not insulated very well, think fiberglass batts that have gaps.
What is the original specification for clearances from the outer wall to combustibles. is it 1” or 2”. I assume no contact is recommended. Thank you, Rick, Michigan
On 2017-11-23 by (mod) -
Pat,
Indeed this is a common complaint that we hear from readers: smoke and odors from a neighbour's chimney.
There are in most communities building regulations about distances from property lines or from nearby buildings that may help sort out what the neighbour is required to do.
In addition we give distances to adjacent buildings, windows, etc. in the "Other Key Articles" listed above on this page.
On 2017-11-23 by Pat
Our next door neighbor has about a 3 foot high metal chimney that vents their oil burner (they moved it to the garage). It's on their lower (garage) roof, and way below the height of their upper roof ridge line from the main part pf the house.
It's also right next to our bedroom windows. We're concerned about fumes, not to mention it's very noisy.
On 2017-04-13 by (mod) -
Anon:
Fire stops or fire blocking where?
The final legal approval of your fireplace installation is of course your local building official.
On 2017-04-13 by Anonymous
on a house with no occupied area above fireplace unit and only a vaulted are fire stops required for wood burner with pipe rated and supplied with unit 20' approx
Question:
(Feb 6, 2013) bill.fletchis@gmail.com said:
Can insulation be put next to the metal chimney in the attic area for a gas furnace
Reply:
Bill, some metal chimneys require an air space while others are rated for zero clearance. What kind of flue is this?
If it's a B-vent, typically you need to leave a 1" clearance around the vent - take a look at the "listed" clearance for your particular product - you'll see that advice in the table above.
Let me know what you find or email me the B-vent product name, specs, or any details you can and we'll research it together.
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In addition to any citations in the article above, a full list is available on request.
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 [Website: /www.house-whisperer.com ] 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 804-873-8534 or by Email: johncranor@verizon.net
Thanks to Luke Barnes for suggesting that we add text regarding the hazards of shared chimney flues. USMA - Sept. 2008.
Thanks to Bryce Olson, New London, CT, for technical editing and correction of clearance distances - 03/2009
Thanks to reader Vic for technical editing and again, correction of clearance distances - 04/2009
NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older 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.
GAMA -
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: CHIMNEY INSPECTION DIAGNOSIS REPAIR . 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
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
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.
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.
Fireplaces, a Practical Design Guide, Jane Gitlin
Fireplaces, Friend or Foe, Robert D. Mayo
NFPA 211 - Standards for Chimneys & Fireplaces, NFPA 211: Standard for Chimneys, Fireplaces, Vents, and Solid Fuel-Burning Appliances, 2006 Edition (older editions and standards are found at the same bookstore)
Principles of Home Inspection: Chimneys & Wood Heating, in (Principles of Home Inspection), Carson Dunlop, Associates, Toronto, Ontario
NFPA 211 - 3-1.10 - Relining guide for chimneys
NFPA 211 - 3-2 - Construction of Masonry Chimneys
NFPA 211 - 3-3 - Termination Height for chimneys
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
In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.