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  1. #1
    Jon mackay's Avatar
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    Default high efficiency pvc vent underground

    I have not seen this before and was not able to find any good references.

    The installation exits through a crawlspace and is underground for a foot or so.

    Also, is the exhaust too close to the a/c unit? Not that they would be running at the same time but is the corrosive gas a concern? I was thinking yes but again was not able to verify.

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  2. #2
    Kary Krismer's Avatar
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    Default Re: high efficiency pvc vent underground

    Are you sure that's not an intake? I would expect it to have a second turn down if it were, but that doesn't mean it isn't.


  3. #3
    Jon mackay's Avatar
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    Default Re: high efficiency pvc vent underground

    Quote Originally Posted by Kary Krismer View Post
    Are you sure that's not an intake? I would expect it to have a second turn down if it were, but that doesn't mean it isn't.
    Yes, I'm sure. They are utilizing the indoor air for intake.


  4. #4
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    Default Re: high efficiency pvc vent underground

    Quote Originally Posted by A.D. Miller View Post
    Yes.



    Yes, it is.
    So how far away does the exhaust need to be from the outdoor unit?


  5. #5
    James Duffin's Avatar
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    Default Re: high efficiency pvc vent underground

    It seems like you need to get a copy of the manufactures installation instructions. This is a unique installation.


  6. #6
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    Default Re: high efficiency pvc vent underground

    I'd be concerned about the soil being above the foundation, possibly covering the rim joist. Looks like the a/c and electrical wiring are all subterranean.

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  7. #7
    Jon mackay's Avatar
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    Default Re: high efficiency pvc vent underground

    It is a unique house. All block wall construction.


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    Default Re: high efficiency pvc vent underground

    Quote Originally Posted by Jon mackay View Post
    It is a unique house. All block wall construction.
    Penetrations below grade is a no-no.

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  9. #9
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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Ken Rowe View Post
    Penetrations below grade is a no-no.
    You mean all those water lines, sewer lines, oil lines, electrical lines, etc., which penetrate through the foundation walls below grade are a "no-no"?

    Jeez, that would make almost every house with a basement a no-no.

    Jon said it was a:
    Quote Originally Posted by Jon mackay View Post
    The installation exits through a crawlspace ...
    If it is a "crawlspace" and not a basement, then the crawlspace floor should be at or above grade, not below grade, that would just lead to water intrusion.

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  10. #10
    Jon mackay's Avatar
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    Default Re: high efficiency pvc vent underground

    It is in fact a crawl space but oddly enough, it is below grade.
    The house is a modernistic, built in the 1930s.. Very unusual but built like a fortress..

    I was not going to raise the issue as being a problem because I can't find any information that states it is not allowed.

    If anyone has information that states otherwise, please let me know.


  11. #11
    Kary Krismer's Avatar
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    Default Re: high efficiency pvc vent underground

    I'm not getting this talk about how crawlspaces should not be below grade. Around here about 100% of crawlspaces are below grade. Is it different elsewhere or am I misunderstanding what is being said?

    Just to be clear though, when a house is built around here typically 3-4 feet of dirt is dug out, the foundation it built, the main floor is built a few inches/feet above grade, and the area below the main floor is called a crawlspace. The only differences between a crawlspace and a basement are whether you can stand up, and a basement usually has a concrete floor.


  12. #12
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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Jerry Peck View Post
    You mean all those water lines, sewer lines, oil lines, electrical lines, etc., which penetrate through the foundation walls below grade are a "no-no"?

    Jeez, that would make almost every house with a basement a no-no.
    Around here water pipes come in through the floor (non structural), sewer pipes are through the floor (non structural), electrical, gas piping etc come in above grade. As you can see by my original post I did not call it a code violation, but then again I'm not a code inspector.

    While there may not be specific Codes or manufacturers instructions to address this issue, sometime you just need to use common sense. Please post ANY documentation supporting penetrating the foundation wall below grade for electrical, air conditioning lines or furnace venting.

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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Ken Rowe View Post
    Please post ANY documentation supporting penetrating the foundation wall below grade for electrical, air conditioning lines or furnace venting.

    Without getting into the technical code aspect and keeping your common sense statement, think about ...

    Footing 12 inches below frost level minimum.

    Pipes 12 inches below frost level minimum.

    Sleeves 2 pipe sizes larger for pipes penetrating through foundation walls.

    There are more, but use your common sense and put those together, you will see that the sleeves are there for, in part, just the purpose we are discussing.

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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Jerry Peck View Post
    Without getting into the technical code aspect and keeping your common sense statement, think about ...

    Footing 12 inches below frost level minimum.

    Pipes 12 inches below frost level minimum.

    Sleeves 2 pipe sizes larger for pipes penetrating through foundation walls.

    There are more, but use your common sense and put those together, you will see that the sleeves are there for, in part, just the purpose we are discussing.
    So where is the sleeve for the furnace vent?

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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Jerry Peck View Post
    Without getting into the technical code aspect and keeping your common sense statement, think about ...

    Footing 12 inches below frost level minimum.

    Pipes 12 inches below frost level minimum.

    Sleeves 2 pipe sizes larger for pipes penetrating through foundation walls.

    There are more, but use your common sense and put those together, you will see that the sleeves are there for, in part, just the purpose we are discussing.
    Quote Originally Posted by Ken Rowe View Post
    So where is the sleeve for the furnace vent?
    Ummmm ... Ken, did you miss this part? "There are more, but use your common sense and put those together, you will see that the sleeves are there for, in part, just the purpose we are discussing."

    Let's see ... "common sense" tells us, at least tells me, that the UNDERGROUND vent would enter and penetrate the foundation wall UNDERGROUND, and, as such, the sleeve, if there were a sleeve, would be UNDERGROUND ... And you are asking me to point it out in that photo?

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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Jerry Peck View Post

    Let's see ... "common sense" tells us, at least tells me, that the UNDERGROUND vent would enter and penetrate the foundation wall UNDERGROUND, and, as such, the sleeve, if there were a sleeve, would be UNDERGROUND ... And you are asking me to point it out in that photo?
    Since when can sleeves terminate under ground? If that PVC vent was sleeved the sleeve should terminate above ground and be sealed. Just like the sleeves for the electrical wiring and a/c lines.

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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Ken Rowe View Post
    Since when can sleeves terminate under ground?
    Whenever something in them is underground, such as underground water pipes, underground sewer pipes, underground electrical conduits, underground ... shall I continue?

    For someone who always professes "common sense" and "not codes" you are not displaying the common sense to recognize all the obvious things that common sense should lead you to jump at and grasp.

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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Jerry Peck View Post
    Whenever something in them is underground, such as underground water pipes, underground sewer pipes, underground electrical conduits, underground ... shall I continue?

    For someone who always professes "common sense" and "not codes" you are not displaying the common sense to recognize all the obvious things that common sense should lead you to jump at and grasp.
    So let's follow your theory. You theorize that there is a 6 inch pipe sleeve (2x the diameter of the vent pipe) below grade on the exterior and open into the crawlspace. That's the way it should be done according to you.

    Not a good building practice in my book. I'll stick with my original statement that penetrations through the foundation wall below grade is a no-no. (as in should be avoided).

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    Default Re: high efficiency pvc vent underground

    My concerns would be, is it installed according to the manufacturer's installation instructions? Ones that I have seen specify intake and exhaust are within a few inches of each other to prevent pressure differential that would cause a shutdown.

    But my main concern is it appears to be too low to prevent snow drifts from covering the pipe. Being non-insulated this could result in the condensation freezing in the pipe. Had it happen until I insulated the pipe.


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    Default Re: high efficiency PVC vent underground

    Quote Originally Posted by Ken Rowe View Post
    So let's follow your theory. You theorize that there is a 6 inch pipe sleeve (2x the diameter of the vent pipe) below grade on the exterior and open into the crawlspace. That's the way it should be done according to you.
    Ken,

    It would help if you would read the posts.

    Quote Originally Posted by Jerry Peck View Post
    Sleeves 2 pipe sizes larger for pipes penetrating through foundation walls.
    See the difference in what I said and what you said I said?

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    Default Re: high efficiency pvc vent underground

    Yes, I did mis-read what you had written. However, the installation is still suspect and not the best way to do it.

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  22. #22
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    Default Re: high efficiency pvc vent underground

    I'm interested in learning more about this type situation.

    The photographed vent termination appears to be smaller than 3". It doesn't look to be more than three pipe diameters from the exterior foundation wall. How could this be horizontal at penetration, properly sleeved through a waterproofed foundation, and offset to its vertical position so close to the foundation and be venting properly?

    I note freeze & frost depths in NYS are significantly deep, esp. Upstate. So this appliance exhaust point would have to be about five feet below grade (yet its a completely sub-level or "below grade" "crawl space", yet using "indoor" air for combustion - with "crawl space" hosting the appliance being completely "below ground" where is this air being sourced? Should I presume the crawl space itself is being heated or unheated? I admit confusion here on the specifics JM offered. He declared it ran "about a foot or so" and I'm wondering if it is only one foot or so below grade, as well as being so close to the foundation wall itself.

    I am curious, with the temperature related shifts/expasion of PVC, a required change of direction for such a vent from below-grade yet within the freeze/frost layer from this through-the-(block?)-foundation-wall sub-terainian CRAWL SPACE, and considering the shifting/heaving of the soil, and the additional cavates of frosting/frozen venting, especially in a low temperature exhaust; and the importantance of having a continuous sealed vent for positive pressure venting appliances, Just how could,should this be expected to reliably work, and remain in-place, and not be stressing or failing at some point of connection (esp. at the appliance itself) or along its length when resisted by frozen soil and exhausting temperatures warmer?

    Snow load heights, and the alcove type almost three-sides restricted location (even if it weren't an A/C unit sitting in the foreground but some other obstruction, also make me wonder about cold swirling wind downdrafts still able to enter the vent, or straight winds.

    I sure hope Bob Harper chimes in on this one.

    I admit I have never seen this tpe of application so far north, so shallow (depth), or so sized. Would a chase with SS or what would be best practice (assuming appliance could not be relocated and obstruction on first floor above which could not be relocated) for venting from within/above the freeze/frost line of a foundation wall?

    Last edited by H.G. Watson, Sr.; 07-03-2010 at 05:06 PM.

  23. #23
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    Default Re: high efficiency pvc vent underground

    HG, The easiest way to prevent this from running below grade would be to install a window well. There are many other options such as a chase up through the roof or simply raising the level up the vent. But just going by the picture and description I'd go the window well route.

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