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L vent and B vent height requirements (C) Carson Dunlop Associates Fire Safety Clearance Requirements between Metal Chimneys & Combustible Materials

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

Adjacent metal flue heights should vary (C) Carson Dunlop AssociatesThis 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.

See CLASS A CHIMNEYS, MetalBestos™

Class A, B-Vent, & 650C Metal Chimney Fire Clearance Requirements

Carson Dunlop's sketch summarizes combustible clearance requirements for the three main types of metal chimneys:

Metal flue clearance requirements (C) Carson Dunlop Associates

Sketch courtesy Carson Dunlop.

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:

  1. The installation instructions for the specific flue vent connector or metal chimney brand and model or product
  2. 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.

Selkirk B-vent embossed notice on the chimmey gives minimum fire clearance distances (C) Daniel Friedman InspectApedia.com

Also see the chimney codes listed below.

Key Articles on Chimney, Flue, & Vent Clearances for Fire Safety & Building Code Compliance

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:

  1. 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
  2. The required separation of metal or insulated chimneys themselves from various building components or combustibles - discussed

    at FIRE CLEARANCES, METAL CHIMNEYS
    and for height above roofs

    at CHIMNEY HEIGHT & CLEARANCE CODE
  3. The required separation of heating appliances (like an oil burner) from heating oil storage (the oil tank) - discussed

    at ABOVE GROUND OIL STORAGE TANK (AST) INSPECTION

 




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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 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.

For example, the MAJESTIC IO Manual for the Ashland Wood Burning Fireplace, 36" model [PDF] Majestic Products A Brand of Hearth & Home Technologies Inc.

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.

Majestic wood burning 36 inch Ashland Fireplace Dimensions and clearance distances - discussed and cited at Inspectapedia.com

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.

Ameri-Vent 6EAL Type B Gas Vent fire clearance distance label (C) Daniel Friedman at InspectApedia.com

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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FIRE CLEARANCES, METAL 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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