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L vent and B vent height requirements (C) Carson Dunlop Associates Type B-Vents Chimney Rooftop Clearances
Type B gas vents fire clearances at rooftop

Metal B-Vent chimney clearance distances above and on the roof:

Clearance distances are given for a gas appliance B-vent at the rooftop.

This article series describes B-vent metal chimneys used for gas-fired appliances. We discuss fire safety, fire clearances, and other gas appliance venting details for b-vent chimneys.

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Type B Gas Vent Rooftop Chimney Height & Clearances

Type B Vent (C) Carson Dunlop Associates

Heights for these both B-Vent and L-Vent types of metal chimney vents are shown in Carson Dunlop Associates [at REVIEWERS] sketches at page top and right here.

[Click to enlarge any image]

The top of the chimney should be at least two feet above anything within a ten-foot radius of the chimney.

Except for flat and very low slope roofs such as those listed in the table below, B-Vents should be at least two feet above the roof surface as well.

See the detailed B-vent chimney rooftop clearance table below.

Also see CHIMNEY HEIGHT & CLEARANCE CODE - separate article that compares the B-vent with other chimney types.

The 1992 Vent Sizing Tables below (and more-recent codes) all require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer's instructions.

Table of Type B-Vent Rooftop Clearance Requirements

Vent caps 12" and smaller may terminate a distance above the roof if 8 feet or more away from a vertical surface as follows:

Table of Rooftop Chimney Clearances for Metal B-Vent Chimneys & Flues
ROOF PITCH - rise/run in inches Minimum Height Above the Roof Surface (1)
Flat to 7/12 1.0 foot above the roof surface (1)
7/12 to 8/12 1.5 feet above the roof surface
8/12 to 9/12 2.0 feet above the roof surface
9/12 to 10/12 2.5 feet above the roof surface
10/12 to 11/12 3.25 feet above the roof surface
11/12 to 12/12 4.0 feet above the roof surface
* Continues to 21/12 pitch at 8.0 feet  

Notes to the table above

  1. measure on the up-roof or "shorter" height side of the chimney
  2. Watch out: while one foot above the roof surface may meet the recommendations for fire clearances, in one-storey buildings or in buildings with heating equipment on the uppermost floor, the total chimney height may be inadquate to establish sufficient and safe draft unless you extend the chimney height by more than these low minimums.
  3. Chimney Vent caps larger than 12" must be located at least 2 feet above the highest point and 2 feet higher than any portion of the building within a horizontal distance of 10 feet.
  4. The 1992 Vent Sizing Tables require that all Type B gas vents terminate above the roof with a listed cap or listed roof assembly in accordance with the manufacturer's instructions.
  5. Details about chimney height & rooftop clearance requirements on buildings for all types of chimneys are

    at CHIMNEY HEIGHT & CLEARANCE CODE

    For details about all types of metal chimneys

    see METAL CHIMNEYS & FLUES
  6. The minimum distance from the top or nearest B-vent chimney component to overhead electrical wires is 3 ft.

    See ELECTRICAL SERVICE DROP

 


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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 2020-10-07 - by (mod) -

There are model or standard prototype building codes that are written at a national level for most countries. State or provincial for local building authorities generally will adopt one of those models and occasionals make some adjustments to them.

If you look in the article index for this page you will find a link to all of the US and Canadian as well as other countries building codes and model codes

On 2020-10-07 by Model

Hi what did you mean by model?

Thanks,

Bob

On 2020-10-06 - by (mod) -

Robert

You're right, chimney heights, or minimum heights above the roof are described in model and local building codes.

On 2020-10-06 by Robert Fleszar

Hi,
I live in the middle unit of a 6 unit townhome with an HOA. I discovered a building code violation and want to correct it and replace a damaged vent pipe and B Vent Cap. The HOA is giving me a hard time wanting to know how high the new pipe will be.

I never heard of an HOA having that control or rule. I thought the height was distracted by the local code?

On 2020-03-10 - by (mod) -

No, Lee, for fire safety there are rooftop clearances given in the article above on this page.

For other readers, Lee's "POC" refers to "products of combustion.

On 2020-03-10 by Lee

Should the height be any hieght as long POC are adequately dispersed

On 2019-10-31 - by (mod) -

The possible concern is for both fire safety (clearances to combustibled) and fatal flue gas leak safety (if the system leaks).

Flexible flue vent connector material, presumably stainless steel) will be single-wall in thickness and even if code-approved to connect a fireplace vent, depending on the temperatures involved, it probably doesn't have the same combustible clearance ratings as a B-vent.

Pretty much everything depends on the specific type, brand, model of gas fireplace being installed. Get installation instructions and parts approvals in writing from the manufacturer.

On 2019-10-31 by Wendy

I have a gas fireplace insert with a flex pipe, and a B Vent at the roof. The insert needs replacing. I see the B Vent at the roof and, when I pull the insert forward a bit, I see a flex pipe out the top of the insert. The fireplace guy tells that B Vent into a flex pipe is bad/illegal. The fuel company/fireplace guy tells me he has never heard of this. Is there a concern?
Wendy

On 2017-11-03 - by (mod) -

Tom, at ADJACENT METAL CHIMNEY SEPARATION https://inspectapedia.com/chimneys/Chimney_Height_Codes_Specifications.php#AdjClr

we note that metal chimneys should be at least 16" (that's 16 inches) apart and that it makes sense to stagger the rain cap heights as well - I agree with your chimney contractor.

On 2017-11-03 by Tom

I have a B vent that was vented by the heating company in a new chimney chase adjacent to a metal chimney flue. The idea was to make a nice, clean look, and not have another hole in the roof. The chimney contractor says I should be concerned about the short distance (about 5 inches) between the two caps due to downdraft into the fireplace. I can't find anything that tells me there's a minimum(?), but I am concerned. Any suggestions?


...

Continue reading at HEIGHT REQUIRED for L VENTS & B VENTS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see TYPE B-VENT CHIMNEY FAQs - questions & answers posted originally on this page

Or see these

Recommended Articles

Suggested citation for this web page

TYPE B-VENT ROOFTOP CLEARANCE 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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