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Thread: Myth Buster

  1. #1
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    Default Myth Buster

    On several previous treads, people have stated a 12 inch straight length of flue pipe is needed on top of the draft hood. I have asked on two different threads for someone to point out the code requirement or manufactures requirements. Both times, there were no answers.

    Last night I sent an e-mail to A.O Smith asking that question, the following is their reply:

    DISCUSSION THREAD
    Response (Brandon Freeman) 05/23/2007 08:59 AM
    Darren,

    Thank you for contacting us. If you are referring to standard atmospheric venting water heaters, then a straight vent run is not a requirement before a bend, although we do recommend it as it allows for better venting. The main thing to insure is that any horizontal run is on an appropriate rise and that the total horizontal is less than 75% of the vertical. Please let us know if we can assist you further.

    Sincerely,
    Brandon



    So, unless someone can show some code requirement, let's put this HI folk-lore to bed right now!


    Darren

    New Jersey Home Inspection - About the House!

    Similar Threads:
    Last edited by Darren Miller; 05-23-2007 at 01:23 PM. Reason: spelling (sic)
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    Default Re: Myth Buster

    Darren,

    Thanks for this. I too have asked about this from local HVA/C technicians and have received a puzzled look. It will be interesting to hear the responses.

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    Default Re: Myth Buster

    Instead of sending that to the water heater manufacturer, send it to the vent manufacturer.

    THEY (the vent manufacturer) are the ones which state and show going vertical 1 foot before turning, and that one foot, to may recollection, is measured from the top of the water heater, not from the top of the draft hood (at least as I remember the drawings showing it).

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Jerry

    Show me the proof;

    Show me code requirements

    Show me manufactures requirements

    Show me show me show me

    I would think the water heater manufacture whould require it if neededl they said NO.

    Show me


    Darren


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    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post

    I would think the water heater manufacture would require it if needed
    Water heater manufacturers send out atmospheric appliances with draft hoods on them, this tells me a lot about the manufacturers.

    A one foot section of straight vent doesn't make an appliance vent better, where do they get this stuff?

    Measured Performance more than just a buzzword

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    Default Re: Myth Buster

    Darren,

    I just reviewed the installation instructions from three B vent manufacturers.

    DuraVent:
    "Connector Rise. Plan a minimum of one foot vertical connector rise
    coming out of each appliance."

    AmeriVent:
    "Wherever possible, install vertical vents directly above
    appliances before beginning any lateral runs. "

    And I could find no such requirements for MetalBestos.

    But, then again, I could very well have missed the specific instruction.

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    Default Re: Myth Buster

    I tried to attach this with my post, but my notebook computer kept crashing (I'm out of town and I suspect it does not like the motel's wireless system ).

    From the Simpson installation instructions: see attached - read #8 right there at the top.

    Attached Files Attached Files
    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Jerry,

    You of all people surprise me.

    Everyone knows when reading a code book what the word 'shall' means.

    When reading your attachment, there is a big difference between 'Plan' and 'Shall'.

    Installation instructions usually include "must"; as in
    "there must be a 12 inch rise before any bends can be installed".

    I take your instructions as, "plan on 12 inches, but if you don't have it, no problem."

    Or take Gunnar quote, "whenever possible" doesn't mean MUST.


    Darren


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    Default Re: Myth Buster

    Oh, yeah. One other thing. Regarding the required draft hood connector. In my area, I never see one. In the AmeriVent instructions, the draft hood connector is listed as optional.

    AmeriVent Products
    (click on the diagrams, specifically "Type B Gas Vent Single Appliance")

    On the same page is a link to download the installation instructions and the item that I quoted is at the bottom of p. 2.

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    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post
    Jerry,

    You of all people surprise me.

    Everyone knows when reading a code book what the word 'shall' means.

    When reading your attachment, there is a big difference between 'Plan' and 'Shall'.

    Installation instructions usually include "must"; as in
    "there must be a 12 inch rise before any bends can be installed".

    I take your instructions as, "plan on 12 inches, but if you don't have it, no problem."

    Or take Gunnar quote, "whenever possible" doesn't mean MUST.


    Darren
    Darren,

    Does *THIS* "SHALL" mean anything to you?

    From the IRC. (bold and underlining are mine).

    - M1307.1 General. Installation of appliances shall conform to the conditions of their listing and label and the manufacturer’s installation instructions. The manufacturer’s operating and installation instructions shall remain attached to the appliance.

    That means *YOU SHALL* follow the manufacturer's installation instructions and *YOU HAD BETTER PLAN ON* that minimum height of 12".



    I have no idea why you insist on being so confused on this, and then continue trying to defend your position on it.


    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Jerry,

    I kind of have to agree with Darren. One B-vent product instructions (DuraVent) uses ambiguous wording, one product (AmeriVent) writes "whenever possible" and another (MetalBestos) does not mention it at all. This apparently means that we must know all of the installation instructions of all of the B-vent manufacturers in order to properly report on them.

    Either that, or we defer on everything.

    Department of Redundancy Department
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    Default Re: Myth Buster

    [QUOTE=Jerry Peck;6677]Darren,

    Does *THIS* "SHALL" mean anything to you?

    From the IRC. (bold and underlining are mine).

    - M1307.1 General. Installation of appliances shall conform to the conditions of their listing and label and the manufacturer’s installation instructions. The manufacturer’s operating and installation instructions shall remain attached to the appliance.


    OK then, is a vent considered an appliance; I think not.


    Sorry Jerry, you're making this up as you go.......


    Darren


  13. #13
    Bob Mayer's Avatar
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    Default Re: Myth Buster

    Quote Originally Posted by DavidR View Post
    A one foot section of straight vent doesn't make an appliance vent better, where do they get this stuff?
    Ever use a double-basin sink where the drains are connected with a tee directly under one of the drains? That is, the straight part of the tee is vertical? The difference in draining speed is very great. The push for water's draining is the same as the push for hot air's tendency to go up the vent, its weight, where the hot air has negative weight. The push is greatest when the flow is aligned with gravity, vertical. This, of course, is why the amount of horizontal travel in a atmospherically-vented vent is limited. The only reason the combustion gases are moving up the vent is that they are marginally lighter than the surrounding air. It doesn't take a whole lot to screw this up and have some of the combustion gases come out the huge hole at the draft hood. So as the combustion gases pass out of the appliance, through the draft hood, and into the vent, we want as much push, with as little friction, as possible. A bend, going into a section that is not vertical, right above the draft hood, will make the upward draft force less than what it would be with a straight, vertical section. Maybe it is a small difference, but when outside winds are set up for backdrafting, or if the combustion air is insufficient, I wouldn't want venting system slowing down the combustion gases just where they can come out into the room.

    So I believe that is why there are reccommendations for a straight section of pipe above the draft hood.

    They may be only recommendations, but if an installation doesn't start out with a straight section of vent where it could, I would call it out. There are advantages in our not being code inspectors. We can, and should, point out where safety could be improved even if the installation meets code. If I were acting for the AHJ I would require a straight section at the draft hood if the installation allowed it based on the installation instructions mentioned in this thread.

    - BOB


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    Default Re: Myth Buster

    Bob:

    OK; you do an inspection and call out a water heater vent needs a straight section of pipe attached to the draft hood.

    The seller then calls a licensed plumber who tells her, the inspector is wrong, It is not a code issue; manufactures RECOMMEND it be installed this way but it's not REQUIRED. She then calls her local AHJ who backs up the plumber.

    Oh, by the way, here's my bill for a $175.00 service call.

    Seller then calls you looking for $175.00 because you believe in the HI foke lore.

    Hey; I'm all for calling ANYTHING out if it's wrong. However, I need back-up, (code requirements or manufactures REQUIREMENTS, not suggestions).


    Darren


  15. #15
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    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post
    Bob:

    OK; you do an inspection and call out a water heater vent needs a straight section of pipe attached to the draft hood.

    The seller then calls a licensed plumber who tells her, the inspector is wrong, It is not a code issue; manufactures RECOMMEND it be installed this way but it's not REQUIRED. She then calls her local AHJ who backs up the plumber.

    Oh, by the way, here's my bill for a $175.00 service call.

    Seller then calls you looking for $175.00 because you believe in the HI foke lore.

    Hey; I'm all for calling ANYTHING out if it's wrong. However, I need back-up, (code requirements or manufactures REQUIREMENTS, not suggestions).


    Darren
    Perhaps I wasn't long-winded enough in my post. I do not believe in the HI folklore, I believe in the laws of fluid flow and thermodynamics.

    From Gunner's post:
    AmeriVent:
    "Wherever possible, install vertical vents directly above
    appliances before beginning any lateral runs. "

    Some of the vent manufacturers give what could be called a recommendation or preference for putting a straight vent section above the draft hood. I explained (or tried to) why this is A Good Thing.

    The issue you make of the financial liability is a good one, and I did not think of it. I would still call it out, as a recommendation, in the case where having a vertical section is possible, but I would explicitly say that the code "probably" does not require it.

    You make an important distinction between requirements and recommendations. I believe that the recommendation is significant enough to mention, and, thanks to your post, I would make it clear that it is a recommendation and not a requirement. I can understand if another inspector would not mention it at all.

    - BOB


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    Default Re: Myth Buster

    Darren,

    You are beginning to sound a bit like Tony M. here.

    You do not need, should not need, code, HIs *CANNOT* *MAKE* anyone do anything.

    Are you forgetting that you are being paid to provide *YOUR* "professional opinion"?

    *MY* "Professional Opinion" *IS NOT* going to contradict the manufacturers opinion.

    If the manufacturer wants (however they word it) something to make something work better, *I* am not going to take it upon myself to say it is not needed.

    I inspected under that concept for over 16 years and NOT ONCE has any seller ended up trying to get me to pay for THEIR (their contractor's, their whomever) errors. The manufacturer wants it, I recommend it, I cannot not (as an HI) make anyone do anything.

    I guess you just don't get the mileage with the way you present your information that I got with the way I presented my information.

    My clients understand that what there are reasons why the manufacturers want what they want, maybe yours don't?

    Bob H. recently, on another thread (which it appears you missed) addressed this very issue, providing the listing information (or something, forgot now) which addresses the very issue you are trying to skirt - maybe Bob will post it again.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Darren,

    You've made a very defensible argument with respect to code. I have not been able to find the 12 inch requirement in any resources I have checked. I am unable to defend what I have been saying for a very long time. I hate you, Darren.

    I do not have the 2002 NFGC, so I can't check their tables to see what they have to say. If you or any respondent on the thread have a copy will you look and report if the tables refer to this subject of length?

    I do remember learning it in a CE course early in my licensed career and I remember it being recommended because of the inefficiencies of heaters and the bends closer than 12 inches having a tendecy to corrode prematurely.

    Let's hear from some plumbers on this issue. And as for Inspectors, what does your local code say?

    For a different take on the use of single wall pipe AT ALL, read this article.
    GAS VENT DESIGN

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    Default Re: Myth Buster

    Jerry,

    You are correct; HI cannot make anyone DO anything. The best we can do is offer our opinion and provide proper back-up to support our opinion.

    Now, rumor has it you are now in (building) code enforcment. Here in NJ, a building inspector is responsible for many areas of the mechanical code.

    A building inspector would (should) never fail an inspection because a manufacture states "whenever possible" in their installation guide. Here in NJ, a contractor has the right to appeal an inspector's decision. If it's found the inspector is wrong, disipline actions (possible lose of license) can be taken.

    On another note, when I was a superintendent, I had a sub contractor dispute my call for his installation of modulines in the ceiling. He stated he "installed 50,000 modulines this way" just because you did it that way for years doesn't make it right.

    See Thom's post above; he's thinking about what he's been saying for years now. He believes he could be wrong. If someone calls him out right now, he has no back-up to prove his call. Maybe he'll find something, maybe he won't. Until someone can show me where a manufacture of a water heater REQUIRES a straight pipe on the draft hood, it's a myth.

    An stop comparing me to other people; any good home inspector needs back-up to prove their claim. Without back-up, your creating more HI folk lore.


    Darren


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    Default Re: Myth Buster

    Actually, what I'm looking for at this point is any support for what I have been saying. As JP said, "You do not need, should not need, code, HIs *CANNOT* *MAKE* anyone do anything.....If the manufacturer wants (however they word it) something to make something work better, *I* am not going to take it upon myself to say it is not needed."

    If I can find support, I'll continue to use it. The closest I have come so far is some published general instructions saying that the vertical run should run as far as possible before a bend, and one drawing showing 6" minimum. Nothing re 12".

    T

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    Default Re: Myth Buster

    http://www.bradfordwhite.com/images/..._44219_00F.pdf

    page 9 requires 12 inches .............

    only it's not the 12 inches you think it is.


    This is clear cut proof.


    Darren

    New Jersey Home Inspection - About the House!


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    Default Re: Myth Buster

    OK, for starters, I've e-mailed three major B-Vent manufactures....


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    Default Re: Myth Buster

    Michael;

    This is another point:

    How many 'B' vents do you see attached to a water heater??


    Darren


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    Default Re: Myth Buster

    Darren
    You make some interesting points. Even if a conclusive answer is not arrived at, this type of discussion should make better inspectors of us all, by making us dig deeper to find to find out.
    Case in point, you stated that a vent is not an appliance
    "OK then, is a vent considered an appliance; I think not."
    I believe the 2006 IRC says it is.
    " APPLIANCE. A device or apparatus that is manufactured and
    designed to utilize energy and for which this code provides specific
    requirements."
    A vent is a manufactured device, designed to use energy (heated air) and has specific code requirements.

    Many times we (HIs) make a recommendation for an item that is "not required" such as GFCI, anti siphon hose bibs, replace FP panels. None of these are required by code, but good practice dictates we mention it.
    At some point in time someone recognized that GFCI were needed, maybe it was years later before it was added to code as a requirement. But some electrician somewhere was using them before it became code, because he knew it was better.

    An appliance connected to a vent without a 12" rise before a turn "MAY" vent properly, much of the time, but with a 12" rise it will vent as good, and probably better, all of the time.

    Whenever I inspect EFIS or vinyl siding I think " what problems may exist that I don't see?". Poor workmanship can cause so many problems later.
    The same as with venting, if there is no rise above the appliance when available, I ask myself "Why is it not available?". Did they not have room for a rise, if not why was it not planned for, what else was not planned for, that I don't see.

    I feel that where minimal is seen as acceptable, substandard is very close.
    If someone is willing to work for minimum wage, they probably are not worth that much.

    You make a good argument, but why?


    ' correct a wise man and you gain a friend... correct a fool and he'll bloody your nose'.

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    Default Re: Myth Buster

    Per a phone conversation with Dale Menges at Simpson Dura-Vent Tech Support:

    For Cat I gas appliances and gas appliances with a draft hood (that is, residential furnaces and WHs in these categories) the 12” requirement is a function of the gamma tables in the NFGC, which start at a minimum 12” rise – without this rise, the vent cannot meet the requirements of the code. There are two exceptions: 1) an appliance listed and tested with some other vent arrangement (for example, a gas fireplace) and 2) a system engineered for a specific application, when stamped plans are present.


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    Default Re: Myth Buster

    This is the e-mail I got back:

    the Gama tables always require a 12" min. rise for sizing category I appliances and appliances with draft hoods. If there is not a 12" min rise then sizing of the venting system must be done by some another approved means. Because we use the Gama tables exclusively for sizing category I appliances and appliances with draft hoods, we would always need a min. of 12" rise.

    Thanks
    Dale Menges
    Product specialist
    Simpson Dura-Vent
    1-800-835-4429


    I admit I have never seen such a table; didn't know it existed. Now, my question is, do manufactures require this table be used, is it referred in any code section?

    Does anyone have a copy they would like to share?

    Rick:

    I don't think a vent connector 'uses' energy, it moves the by products to the exterior.

    Man oh man, this debate can go on forever.....

    But at least we're having fun


    Darren


  26. #26
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    Default Re: Myth Buster

    From the FAQ at gamanet.org:

    Where can I find the GAMA Venting Tables?GAMA has not published venting tables since 1991. The venting tables in the current National Fuel Gas Code incorporate the information that was contained in those "GAMA" venting tables. That document can be ordered from the American Gas Association or the National Fire Protection Association.

    The tabes can be found here.

    Last edited by Bob White; 05-24-2007 at 01:59 PM.

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    Default Re: Myth Buster

    Thanks, Bob. That's what I was looking for last night, but didn't have the NFGC.

    The only reason some people get lost in thought is because it's unfamiliar territory.
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    Default Re: Myth Buster

    Quote Originally Posted by Bob Mayer View Post
    Ever use a double-basin sink where the drains are connected with a tee directly under one of the drains? That is, the straight part of the tee is vertical? The difference in draining speed is very great. The push for water's draining is the same as the push for hot air's tendency to go up the vent, its weight, where the hot air has negative weight. The push is greatest when the flow is aligned with gravity, vertical. This, of course, is why the amount of horizontal travel in a atmospherically-vented vent is limited. The only reason the combustion gases are moving up the vent is that they are marginally lighter than the surrounding air. It doesn't take a whole lot to screw this up and have some of the combustion gases come out the huge hole at the draft hood. So as the combustion gases pass out of the appliance, through the draft hood, and into the vent, we want as much push, with as little friction, as possible. A bend, going into a section that is not vertical, right above the draft hood, will make the upward draft force less than what it would be with a straight, vertical section. Maybe it is a small difference, but when outside winds are set up for backdrafting, or if the combustion air is insufficient, I wouldn't want venting system slowing down the combustion gases just where they can come out into the room.

    So I believe that is why there are reccommendations for a straight section of pipe above the draft hood.

    They may be only recommendations, but if an installation doesn't start out with a straight section of vent where it could, I would call it out. There are advantages in our not being code inspectors. We can, and should, point out where safety could be improved even if the installation meets code. If I were acting for the AHJ I would require a straight section at the draft hood if the installation allowed it based on the installation instructions mentioned in this thread.

    - BOB

    I would worry more about the draft hood than the one foot section of pipe.

    Measured Performance more than just a buzzword

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    Default Re: Myth Buster

    I don't know about anyone else, but I am still having a problem with the 12" thing. Once again, not all of the manufacturer's installation instructions specify this and the requirement is buried really deep in technical tables that we cannot really be expected to find it when needed. Is it required on all B-vents, even those that do not specify it? I understand that it is a good idea, but is it required?

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    Default Re: Myth Buster

    Gunnar;

    I haven't read the whole thing yet but,

    The simple answer in NO. (I know, here we go again)

    If you look at the GAMA venting tables, go to page 7 figure 12; that refers you back to table 8 which has a rise (R) for each appliance.

    Now, also on page 7, figure 9 & 10 refers you back to tables 5 & 6 which show no rise. Hence, no rise is needed when venting a single appliance.


    Darren


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    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post
    Gunnar;

    I haven't read the whole thing yet but,

    The simple answer in NO. (I know, here we go again)

    If you look at the GAMA venting tables, go to page 7 figure 12; that refers you back to table 8 which has a rise (R) for each appliance.

    Now, also on page 7, figure 9 & 10 refers you back to tables 5 & 6 which show no rise. Hence, no rise is needed when venting a single appliance.


    Darren
    Darren,

    Where do you see "no rise"?

    The "NR" stands for "Not Recommended", i.e., you have to keep going across the table until you get to one which shows what is allowed.

    By the way, those figures which shows R1, R2, etc., that stands for "connector rise".

    With two appliances, you will have a connector rise with at least one of them (because if cannot also go straight up, it must go horizontally for some distance, thus the connector must rise some amount.

    Check out Table 3, you will see "Connector Rise" in the right of the first column - the shortest connector rise is "1 foot". This is for two or more appliances connected together into a common vent.

    Now, with a single appliance, the connector and vent (or just vent if the Type B vent is connected to the appliance with no 'connector') has a total rise which also equals the overall height of the vent. That 12" rise is still needed to get the draft going before making that first offset. Additionally, the lateral offset with two 90 degree elbows is included in the table for vent sizing, as in Table 1 and Table 2. Each additional 45 elbow reduces the rating by 5% and each additional 90 elbow reduces the rating by 10%. You will notice in Table 1 and Table 2 that there is a lateral (offset) length in the right of the first column.

    The referenced GAMA Venting Tables show a total lateral distance of 100% of the total height, the IFGC only allows a lateral distance of 75% of the total height.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Jerry,

    Where on tables 1,2, 5 & 6 does it show or specify a rise?
    I see it on table 4 & 7, but not on 1,2,5 & 6.

    Darren


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    Talking Re: Myth Buster

    I Believe Darren is the Winner, Jerry looses


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    Default Re: Myth Buster

    NR=no requirement where i come from


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    Default Re: Myth Buster

    Ahh, Y'all are making my foot hurt more than it should! (long story)

    What is wrong if a gas WH does not have a 12" length of pipe on the draft hood? If this is wrong, who or what says it is wrong?

    Then we need to look at the WH manufacturer. If they don't require the 12" section, but the pipe manufacturer does, then who is right?

    Now to throw a wrench into the gears; what about those Flex B vents that bend a few inches above the draft hood?

    ---------------------------

    Scott
    Confusion is only a state of mind, or a good bottle of single malt!


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    Default Re: Myth Buster

    Quote Originally Posted by brian schmitt View Post
    NR=no requirement where i come from
    Brian,

    Look at page 1 of the referenced link.

    It states what NR means.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post
    Jerry,

    Where on tables 1,2, 5 & 6 does it show or specify a rise?
    I see it on table 4 & 7, but not on 1,2,5 & 6.

    Darren
    You also see rise on 3 and 8.

    I stated:
    With two appliances, you will have a connector rise with at least one of them (because if cannot also go straight up, it must go horizontally for some distance, thus the connector must rise some amount.

    Check out Table 3, you will see "Connector Rise" in the right of the first column - the shortest connector rise is "1 foot". This is for two or more appliances connected together into a common vent.

    Now, with a single appliance, the connector and vent (or just vent if the Type B vent is connected to the appliance with no 'connector') has a total rise which also equals the overall height of the vent. That 12" rise is still needed to get the draft going before making that first offset. Additionally, the lateral offset with two 90 degree elbows is included in the table for vent sizing, as in Table 1 and Table 2. Each additional 45 elbow reduces the rating by 5% and each additional 90 elbow reduces the rating by 10%. You will notice in Table 1 and Table 2 that there is a lateral (offset) length in the right of the first column.
    The tables you pointed out which show a rise are all for two or more appliances, the tables you pointed out which do not show a rise are all for single appliances.

    I explained the differences (tried to anyway).

    Jerry Peck, Construction / Litigation Consultant
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    Cool Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post
    Jerry,

    Where on tables 1,2, 5 & 6 does it show or specify a rise?
    I see it on table 4 & 7, but not on 1,2,5 & 6.

    Darren
    Darren, if you read the heading of those tables, you will see they refer to the capacity of vents and chimneys--those are not vent connector sizing charts, hence no need for a connector rise.

    Dude, you need to take some vitamin V. Why are you so worked up?

    Look, There are numerous references, both direct and indirect that make a case not to elbow off an appliance collar. The Simpson Dura-Vent Sizing Handbook is full of them. The venting tables were developed by Battelle Labs for the Gas Research Institute. They took empirical data and loaded it into a computer running a program called VENT-II, which then developed these tables and charts. Since every conceivable configuration cannot be tested, they developed the most common. The charts start at a 12' vent connector rise because during the actual live burns, they would often get spillage from the sudden resistance of an ell. Each 90 degree ell derates the vent 10%. Why take a 10% hit right off the appliance collar? Quoting GAMA, The vent connector should be routed to the vent utilizing the shortest possible route" . Then, from the IFGC 503.10.6 Flow Resistance. A vent connector shall be installed so as to avoid turns or other construction features that create excessive resistance to flow of vent gases." There isn't much more you can do to resist flow than sticking a 90 degree ell right on top of a draft hood. This is precisely the kind of thing this code section is talking about. Since there are other ways of resisting flow such as adding a dozen elbows, they decided to lump it all into this one broad statement. FYI, those listed flexible connectors have a broad radius bend so they offer less resistance than your typical sheetmetal 90.

    Let me ask you this: What are you inspecting for? I mean, are you performing a code compliance inspection or are you providing a general inspection to ascertain the suitability of this house for human habitation, durability and maintenance concerns? If you give a hoot about your client's safety, the maximum performance of the appliance, the durability of the equipment, indoor air quality, and overall value of the home, you would call out those issues that you know to be a problem or potential problem. Let me quote Benjamin Thompson on this matter:" The whole mystery, therefore, of curing smoking chimneys, is comprised in this simple direction; find out and remove those local hindrances which forcibly prevent the smoke from following its natural tendancy to go up the chimney; or rather, to speak more accurately, which prevent its being forced up the chimney by the pressure of heavier air of the room." From the Collected Works of Count Rumford, 1796 That's right, Seventeen Ninety-Six. We have known in writing for 211 years not to put things in the way of smoke if you want it to get out of the building.

    Now, let me add other considerations to this discussion:
    I think we all are aware of the phenomenon of depressurization of modern homes. By weatherization efforts, we tighten the home, which exacerbates the Stack Effect. By leaving upper level leaks in the thermal envelope such as attic access, lights, and fans, we provide a pathway for passive exfiltration. Then, we install powerful exhaust fans and appliances that remove large quantities of air from the thermal envelope. We place our atmospherically vented heating appliances in confined spaces with inadequate makeup air then install a clothes dryer in the Combustion Appliance Zone (CAZ) to insure we suck this room inside-out. Then, in the face of all this, we see Cat.I vented appliances with draft hoods, which can provide a convenient means of spilling dangerous flue gases back into the home. We use single walled vent connectors, which lose heat to the room thereby causing a cooler stack which translates into weaker draft and condensation, which will rot out the venting. Condensation robs BTUs from warming a flue thereby inhibiting draft as the appliance first fires up. We install our appliances where it suits us instead of as Count Rumford points out, which would mean vented straight up off the appliance collar. In the face of all this, you are not concerned about putting an elbow right at the collar? We know through testing by the Canada Mortgage and Home Corporation the typical draft hood equipped water heater can reliably backdraft at only 3 Pascals of depressurization. This is a mere 0.012 inches of water column. So, with the deck stacked against you like this, you're not going to say something about the lack of vent rise? Boy, you sure are making it easy for the Discovery process....

    Short or no vent connector rise is a bad practice--period. I don't know what else to say to get this point across.

    Keep the fire in the fireplace.

  39. #39
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    Default Re: Myth Buster

    Quote Originally Posted by Bob Harper View Post
    The venting tables were developed by Battelle Labs for the Gas Research Institute. They took empirical data and loaded it into a computer running a program called VENT-II, which then developed these tables and charts. Since every conceivable configuration cannot be tested, they developed the most common. The charts start at a 12' vent connector rise because during the actual live burns, they would often get spillage from the sudden resistance of an ell. Each 90 degree ell derates the vent 10%. Why take a 10% hit right off the appliance collar? Quoting GAMA, The vent connector should be routed to the vent utilizing the shortest possible route"

    Short or no vent connector rise is a bad practice--period. I don't know what else to say to get this point across.

    This is where I have a problem we are being taught to take these venting tables as the gospel when they are based on a computer program simulation?

    There is absolutely no real world field testing data that went into that program, I could not begin to tell you how many appliances I've tested with elbows coming off the draft hoods that were actually venting.

    On the other hand there are numerous appliances I've tested that had flues going straight up with no elbows at all, these were not venting at all.

    Each appliance needs to be tested for the environment it is installed in as that particular installation cannot be accounted for in any computer program.

    Measured Performance more than just a buzzword

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    Cool Re: Myth Buster

    Amen DavidR! Codes, charts and guides are exactly that---guides. I've never met a heater or fireplace that could read a code book. These things tend to do what they want to. When you take into acct. all the variables I posted plus a bunch I either left out or we haven't learned to consider and it is anybody's guess whether it will work or not. These charts mean that under the controlled conditions in a lab, they got a few venting configurations to work then interpolated the rest.

    Guys, DavidR practices what he preaches and he preaches testing pretty strongly. He has taken training then applied it and knows when you ASSume, what happens. He is on a mission to get the HVAC industry to test every installation and quit guessing. He continues with his passion because when he himself is testing, he finds things all the time that would not have been discovered had he not tested. That's like me and looking up chimneys. We know that statistically speaking a high percentage have a problem. The inspection and testing help you uncover how many problems and their scope.

    Codes do Not guarantee performance! Codes are Minimum standards that often must be exceeded.

    David, I see them venting everyday as you have. It also depends a lot on the conditions present. While I'm there is a snapshot in time. I look closely at the top of the WH for signs of frequent prolonged backdrafting such as corrosion, heat damage to paint, crud on top of the unit, melted pipe insulation, etc. Also look for soot trails from the TPR valve. I cannot guarantee they will fial but I state with confidence an ell off the top is more prone to spillage than having proper vent rise.


    Let me ask you this: how many of you would red flag this setup and why: 40 mbtu gas water heater common vented with a 120 mbtu fan assised 80% gas furnance. The vent connector is attached directly to the WH flue collar and there is a Field Controls MG-1 double acting barometric damper installed in a tee off the WH instead of a draft hood. How would you report this? David, you'll love this discussion!

    Keep the fire in the fireplace.

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    Default Re: Myth Buster

    Bob,
    Sometimes your quizzes are helpful to me and sometimes they aren't. This is an "aren't". Rather than having to sift through all the best guess efforts of those of us who are certain to diagnose incorrectly, it would be more beneficial (for me) if someone like you or David R would use the same example and explain why it is incorrect. I could then use the explanation to help recognize and identify problems in the field, as well as a study aid when I'm reading. Just my opinion.

    The only reason some people get lost in thought is because it's unfamiliar territory.
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    Default Re: Myth Buster

    Quote Originally Posted by Bob Harper View Post
    Let me ask you this: how many of you would red flag this setup and why: 40 mbtu gas water heater common vented with a 120 mbtu fan assised 80% gas furnance. The vent connector is attached directly to the WH flue collar and there is a Field Controls MG-1 double acting barometric damper installed in a tee off the WH instead of a draft hood. How would you report this? David, you'll love this discussion!
    OK, I can understand the water heater and the furnace part. But, I don't have a clue what the other stuff is. This must be one of them those Yankee setups!

    Way over my head.

    Scott Patterson, ACI
    Spring Hill, TN
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    Default Re: Myth Buster

    Bob & Jerry,

    I am still having problems with this. As near as I can tell, the tables require a 1 foot vent connector between the draft hood and the vent/flue. Does this mean that that you must use a 1 foot length of single walled pipe and cannot connect the draft hood directly to a B vent?

    Once again, I will have to agree with Scott and Darren. The specifics of this are buried so deep that many HVAC guys aren't even aware of it, much less practice it. I use code or manufacturers' installation instructions to reinforce the comments and recommendations that I make. There is a loss of credibility when I note a potentially hazardous condition, but am unable to come up with clear documentation that I can use as a reference, even if my recommendation is correct. That is why I need documentation that is easy to understand, and I expect that is Darren's reason for being frustrated as well. While these tables are no doubt clear to Bob and Jerry, the average homeowner, heating contractor, plumbing contractor and even building inspector does not get it. Heck, I don't get it. In addition, the reference that we are using is for Catagory 1 Central Furnaces, not water heaters. Not that that makes any functional difference, but when citing this as a reference, it would carry more weight if it included water heaters in the title. Once again, I was unable to find the 12" vertical requirement in the manufacturer's installation instructions, other than DuraVent.

    Realistically, what is necessary is "Thou shalt have a 12" minimum vertical connector above the draft hood on all Catagory 1 gas appliances" included in the code, and we do not have that.

    Department of Redundancy Department
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    Default Re: Myth Buster

    Gunnar,

    Go to the IFGC, page 90, Table 504.2(1), then to page 96, Table 504.2(3).

    There are tables for 'single wall connectors' and tables for 'Type B double wall connectors'.

    Review all the tables and what they are for, you will find many different applications listed in those tables.

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    A great site to check out on barometric dampers is FIELD CONTROLS, LLC - CAS, UV-AIRE, SWG, IAQ, Solutions for the Great Indoors.

    They operate in direct contradiction to the purpose of a draft hood, they actually attach the appliance to the flue.

    You make a great observation about only being there for a snapshot Bob, thats why we have to be thorough in our diagnostic skills.

    We might not get another chance to visit that home, one reason I always recommend low level monitors to anyone who lives in a home.

    Measured Performance more than just a buzzword

  46. #46
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    Default Re: Myth Buster

    "40 mbtu gas water heater common vented with a 120 mbtu fan assisted 80% gas furnace..."

    My understanding is that a natural draft appliance should not share a flue with a power-vented appliance... is this correct?


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    Default Re: Myth Buster

    Quote Originally Posted by Michael Thomas View Post
    My understanding is that a natural draft appliance should not share a flue with a power-vented appliance... is this correct?
    No. The tables even include calculations for (in the two or more appliances connected to a common vent) two fan assisted appliances, two natural draft appliances, and a fan assisted appliance with a natural draft appliance.

    Refer to Table 504.3(1) on page 106, go down to the bottom table which shows the Common Vent Capacity. You will see 'Fan+Fan' (all appliances are fan assisted), 'Fan+Nat' (at least one is fan assisted and at least one is natural drat), 'Nat+Nat' (all are natural draft).

    Jerry Peck, Construction / Litigation Consultant
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    Default Re: Myth Buster

    Thanks.


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    Cool Re: Myth Buster

    Fan assisted is not power vented. It is fan assisting a natural vent, hence it is still Cat. I.

    Power vented, meaning positive flue gas pressure is either Cat. III or IV.

    An 80% fan assisted furnace is not power vented but Cat. I natural vent, fan assisted. Therefore, you use those columns in the Gas code charts for Fan Assisted. I agree with DavidR, after you've done what the code says, then test to confirm it works.

    So, I still ask you home inspectors, which I am not: what would you do if you found a double acting baro. on the WH, which is common vented with a fan assisted furnace? How would you address this? C'mon, you see it all the time so don't be shy.
    Bob

    Keep the fire in the fireplace.

  50. #50
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    Default Re: Myth Buster

    Bob,

    I have never seen that setup before. If there is no room for a WH draft hood, an inline draft box with the open bottom (don't know the official name)would be installed.

    Nonetheless, if i saw that installation, I would check out the baraometric damper at the website. The installation seems to be confirmed by the description for the damper. Quote "The MG-1 baraometric damper is also recommended for use on gas atmospheric appliances where a draft hood cannot be installed, and can improve combustion stability and draft on many gas atmospheric installations with venting problems."


    As long as there's no backdrafting with the furnace inducer fan, I would be OK with it.


  51. #51
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    Default Re: Myth Buster

    There you go.

    If it is not functioning properly, write it up. If a short rise is functioning properly and there is room, recommend improvements (we all agree that increasing the rise at the draft hood will improve function, right?). Also: You cannot always assure it will draft properly under different and all conditions (similar language should be included in the report).

    If there is no room and the appliance is not backdrafting, recommend relocation upon replacement. Again, functioning properly, but cannot assure function under all conditions.

    That is how I handle it.

    Bob


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    Default Re: Myth Buster

    The installation instructions:

    http://www.fieldcontrols.com/pdfs/01984600.pdf

    outline a good deal of information a HI can check visually, including a number of prohibited installation locations. It also states that initial adjustment (and presumably later establishing a correct adjustment) requires a combustion analyzer.


  53. #53
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    Default Re: Myth Buster

    Bob,

    From the MG-1 literature:

    "Because it is double-acting, it opens out to relieve positive vent system pressures as low as .01". Draft adjustments using weights are simple and accurate from .01" to .1"..."

    Does this mean it's spilling exhaust gases into the structure?


  54. #54
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    Default Re: Myth Buster

    The gate will swing outward & relieve a downdraft condition or positive flue pressure scenarios.
    This is the whole purpose in fitting the barometric with a manual reset spill switch tied in with the thermocouple by means of a junction block.

    Very rarely does a barometric spill, draft hoods do it on a regular basis with no means of protection, which would you rather see installed?

    Measured Performance more than just a buzzword

  55. #55
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    Default Re: Myth Buster

    "Let me ask you this: how many of you would red flag this setup and why: 40 mbtu gas water heater common vented with a 120 mbtu fan assised 80% gas furnance. The vent connector is attached directly to the WH flue collar and there is a Field Controls MG-1 double acting barometric damper installed in a tee off the WH instead of a draft hood. How would you report this? David, you'll love this discussion!.."

    Bob, what should the finding be in this case?


  56. #56
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    Cool double acting baro instead of listed draft hood

    It is a repair method being taught by the National Comfort Institute to solve problems properly diagnosed through testing. This enters that "Twilight Zone" because the unit was not tested or listed with this set up but on site performance testing was used to direct this modification be done. The ultimate test is how it performs. If the unit operates within mfr.s specs, has acceptable combustion performance, is not over or underfiring or experiencing any phenomena that could cause early component failure, then no harm, no foul. However, should something go wrong, it would boil down to a battle btw mfr and technician if these modifications caused a problem. Until there is a problem, there cannot be negligence. Depending upon your state's laws, there may still exist a "construction defect". If you perform work that poses a risk of hazard to the occupants, there may exist a "breech of duty" on the part of the technician. Of course, all this would have to be duked out in court.

    When debating repairs outside the scope of the product listing, there is a never ending battle btw following the letter of the law versus fixing it. Codes, standards, and books cannot guarantee performance. If you install to the listing but don't test and there is a problem, you are putting your client at risk. If you install to the listing, notice a problem, and make proper written notice to the homeowner that you are putting the problem back on the mfr. and not to use it until they resolve it, you are in pretty good shape. If you make unrecognized (by the mfr.) repairs and nothing ever goes wrong and your repairs prevented a problem, you are a hero. If you install to the listing and leave a problem, whether diagnosed or not, you are on dangerous ground.

    Keep in mind, you can get an engineer to state almost anything you need one to if you look hard enough. Always seems to be some guy willing to put his license and reputation up against codes and standards.

    I guess it boils down to the laws of probability and risk. What is the more hazardous choice?

    Keep the fire in the fireplace.

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    Default Re: Myth Buster

    Bob, what do you see as being the Hi's proper role here., and what as the reasonable span of knowledge from the conscientious HI?


  58. #58
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    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post
    Bob:

    OK; you do an inspection and call out a water heater vent needs a straight section of pipe attached to the draft hood.

    The seller then calls a licensed plumber who tells her, the inspector is wrong, It is not a code issue; manufactures RECOMMEND it be installed this way but it's not REQUIRED. She then calls her local AHJ who backs up the plumber.

    Oh, by the way, here's my bill for a $175.00 service call.

    Seller then calls you looking for $175.00 because you believe in the HI foke lore.

    Hey; I'm all for calling ANYTHING out if it's wrong. However, I need back-up, (code requirements or manufactures REQUIREMENTS, not suggestions).


    Darren

    Other side of this coin is that you do the inspection and don't call it out... a couple years later the house sells and the inspector does call it. HVAC guy agrees and you get the angry call from your buyer of a couple years ago.

    To me, this is what sometimes sucks about our industry... We can spend hours learning about something and honestly do our best to help our client and still get burned. The seed for this 'flower' of debate only needs two contractors within a given industry to disagree or interpurt something different and happen in at the right (or for us wrong) time and we look bad.


  59. #59
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    Default Re: Myth Buster

    Sub-Panels........Discuss


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    Default Re: Myth Buster

    Quote Originally Posted by Dan Phillips View Post
    Sub-Panels........Discuss
    Which types?

    Astute Class?

    Virgina Class?

    Swifture/Trafalgar Class?

    Los Angeles Class?

    Akula Class?

    Resolution Class?

    One of the old U-Boats?

    You've got to me a lot more specific when talking about subs and their panels.

    Jerry Peck, Construction / Litigation Consultant
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  61. #61
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    Default Re: Myth Buster

    We All Live in a Yellow Class?

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
    www.ArnoldHomeInspections.com

  62. #62

    Default Re: Myth Buster

    Quote Originally Posted by Darren Miller View Post

    Last night I sent an e-mail to A.O Smith asking that question, the following is their reply:

    DISCUSSION THREAD
    Response (Brandon Freeman) 05/23/2007 08:59 AM
    Darren,

    Thank you for contacting us. If you are referring to standard atmospheric venting water heaters, then a straight vent run is not a requirement before a bend, although we do recommend it as it allows for better venting. The main thing to insure is that any horizontal run is on an appropriate rise and that the total horizontal is less than 75% of the vertical. Please let us know if we can assist you further.

    Sincerely,
    Brandon

    New Jersey Home Inspection - About the House!
    O.K. Help me out here. they state that the "total horizontal is less than 75% of the vertical." Which vertical? From the heater to the bend? From the horizontal connection to the roof?


  63. #63
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    Default Re: Myth Buster

    Any opinions on this set up? First one I've seen.

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    Default Re: Myth Buster

    Quote Originally Posted by Rick Hurst View Post
    Any opinions on this set up? First one I've seen.
    You vent with the materials you have, not the materials you wish you had. Apologies to D. Rumsfeld.

    "There is no exception to the rule that every rule has an exception." -James Thurber, writer and cartoonist (1894-1961)
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  65. #65
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    Default Re: Myth Buster

    Quote Originally Posted by Rick Hurst View Post
    Any opinions on this set up? First one I've seen.
    Is that a fan motor/blower hooked up to the vent?


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