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    B vent and turbine vent clearance

    B vent and turbine vent clearance

    New postby Marc M on Sun Jun 14, 2009 11:02 am

    Jerry,
    Are there minimum clearances between B vents and attic ventilation such as turbine or a dormer vent?
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    Re: B vent and turbine vent clearance

    New postby Jerry Peck - Codeman on Sun Jun 14, 2009 3:48 pm

    Hi Marc,

    I've been looking but have not found anything in the codes or the manufacturers' installation instructions I have about Type B Gas termination clearances from openings, mechanical vents, yes, but not gravity flow vents.

    I'll send out a couple of e-mails tomorrow (Monday) and see what I find.

    In the meantime I am sending an e-mail for an expert in this field to see if they know.
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    Re: B vent and turbine vent clearance

    New postby Marc M on Mon Jun 15, 2009 1:24 am

    Fantastic. Thanks for your service.
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    Re: B vent and turbine vent clearance

    New postby Jerry Peck - Codeman on Mon Jun 22, 2009 10:07 am

    Hi Marc,

    Also notice that there is no storm collar on the vent visible to the right of the turbine, the vent beyond the turbine is not visible at the storm collar height.

    So far I have not found anyone or any instructions which knows of a minimum spacing limitation. This is one of those common sense things one knows not to do - one simply knows not to allow contaminated combustion by-products to re-enter the building through any building opening (which includes attic vents) as doing so would be the same as simply venting the gas appliance into the building and not bothering to install a vent.

    That said, code does not address "common sense", if the code did, the code would be so large as to be unusable - think of all of the "common sense" items which would need to be included, one code would be like a 32 volume set of Encyclopedia Britannica.

    However, after doing the research, I am left with the code which requires:
    - " ... are located less than 8 feet (2438 mm) from a vertical wall or similar obstruction shall terminate not less than 2 feet (610 mm) above the highest point where they pass through the roof and not less than 2 feet (610 mm) above any portion of a building within 10 feet (3048 mm) horizontally."

    I agree that an attic turbine vent is not a "vertical wall", but ... could it be considered a "similar obstruction" in that it could restrict the free flow of air around the vent and thus restrict the venting?

    This brings up the idea where a chimney (not a vent) is required to be 3 feet high minimum, or 2 feet higher than any part of any structure within 10 feet, which means that chimneys with multiple flues have a built-in problem of which one is higher than the other, or are both allowed to be the same height? As soon as one is higher, the other is required to be raised 2 feet above the one within 10 feet - does that require a race to the sky or are both allowed to be the same height?

    Would that attic turbine vent actually be a "similar obstruction"? If so, then the vent would need to be 8 feet away, or 2 feet higher than the attic turbine vent. If not, then there is only common sense telling you not to allow combustion by-products to be drawn back into the building.
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    Re: B vent and turbine vent clearance

    New postby Hearthman on Mon Jun 22, 2009 10:54 am

    Actually, the answer is right under our noses. IFGC 503.5.4 Chimney terminations ....."and is at least 2 feet (610mm) higher than any portion of a building within a horizontal distance of 10 feet (3048mm)."

    We tend to think of this rule pertaining just to adjacent gable walls and such but it includes roof turbines because they are a "portion of a building". By locating 2 feet above this feature of the building, you get the flue gas outlet into clear, undisturbed wind and above this opening. Even though turbines normally exhaust, all it takes is a wind eddy to recirculate air. By maintaining this separation, you should reasonably prevent recirculation of flue gases. Now, if you want, you could cite an ASHRAE Standard, 62.1, Ch. 5 that deals with such separations from 'hazardous exhausts' at a min. 15ft for normally bad stuff and 30 ft. separation for extra bad stuff. Based upon personal experience, I find the 2/10 rule sufficient.

    Now, looking at the photo provided, I note severe condensation damage on the vent to the right with the Star Kap. I would have a qualified technician inspect and test that appliance because something is not right there. We now know you must extend this vent to get above the turbine by 2ft., which will allow you to replace that damaged pipe but why is it condensing so badly? Those Star Kaps (Field Controls) usually work really well so I would doubt it is a problem unless it is causing the condensate to drip all over the vent exterior. That vent looks to be exiting and an angle so something is up. Possibly a smaller single walled pipe sleeved inside a larger B-vent? Also, where's the storm collar? :?:

    I see another B-vent down the hip, which probably will need to be extended.
    HTH!
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    Re: B vent and turbine vent clearance

    New postby Jerry Peck - Codeman on Mon Jun 22, 2009 11:37 am

    Hi Hearthman,

    Thank you for responding.

    Hearthman wrote:Actually, the answer is right under our noses. IFGC 503.5.4 Chimney terminations ....."and is at least 2 feet (610 mm) higher than any portion of a building within a horizontal distance of 10 feet (3048 mm)."


    However, I have a question: The IFGC does not apply to single-family dwelling units and that is not a chimney, thus does that still apply?

    The IRC for Type B Gas vents has different requirements, and does not specifically state the same as for chimneys.

    We tend to think of this rule pertaining just to adjacent gable walls and such but it includes roof turbines because they are a "portion of a building". By locating 2 feet above this feature of the building, you get the flue gas outlet into clear, undisturbed wind and above this opening.


    Thus, my referencing the IRC requirements for Type B Gas Vents being 8 feet from vertical obstructions would pertain as well? I was not sure if they would.

    Though turbines normally exhaust, all it takes is a wind eddy to recirculate air. By maintaining this separation, you should reasonably prevent recirculation of flue gases.


    That was my concern, yes.

    Now, if you want, you could cite an ASHRAE Standard, 62.1, Ch. 5 that deals with such separations from 'hazardous exhausts' at a min. 15ft for normally bad stuff and 30 ft. separation for extra bad stuff. Based upon personal experience, I find the 2/10 rule sufficient.


    Okay, now you are getting into what really might help!

    Here is another question, that references "hazardous exhausts", what defines an "exhaust"? In the IRC it refers to mechanically exhausted exhausts, and a Type B gas vent is simply a hole up through the structure which vents stuff out by gravity. Is a Type B gas vent considered an "exhaust"?

    If so, then the IRC "Exhaust Systems" would address this:
    - From the 2006 IRC. (underlining and bold are mine)
    - - M1501.1 Outdoor discharge. The air removed by every mechanical exhaust system shall be discharged to the outdoors. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.
    - - - Exception: Whole-house ventilation-type attic fans that discharge into the attic space of dwelling units having private attics shall be permitted.

    However, that again refers to "mechanical" exhausts.
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    Re: B vent and turbine vent clearance

    New postby Marc M on Thu Jul 02, 2009 12:51 am

    From the 2006 IRC. (underlining and bold are mine)
    - - M1501.1 Outdoor discharge. The air removed by every mechanical exhaust system shall be discharged to the outdoors. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

    This looks good jerry.
    I agree that conventional wisdom should take priority in a grey-ish area such as this.
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    Re: B vent and turbine vent clearance

    New postby Jerry Peck - Codeman on Thu Jul 02, 2009 8:13 am

    Marc M wrote:From the 2006 IRC. (underlining and bold are mine)
    - - M1501.1 Outdoor discharge. The air removed by every mechanical exhaust system shall be discharged to the outdoors. Air shall not be exhausted into an attic, soffit, ridge vent or crawl space.

    This looks good jerry.


    Hi Marc,

    The problem with that code section is that it is referring to "mechanical" exhaust systems and Type B Gas Vents are "natural draft" exhaust systems - meaning that code section does not apply to Type B natural draft systems.

    That section would apply to fan-assisted and direct vent systems which are mechanical draft exhaust systems.
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