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Thread: Connecting New PVC Pipe Vent to Existing Cast Iron Vent Pipe in a Wall for Toilet

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    DIY Senior Member DanMcD's Avatar
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    Default Connecting New PVC Pipe Vent to Existing Cast Iron Vent Pipe in a Wall for Toilet

    My Plumber made the connection of a new PVC pipe vent to my existing cast iron vent pipe which is in the wall for Toilet. The connection is about 8 inches above the floor. This connection is higher than the toilet or sink drain pipes, because they are all below the floor in the crawl space.

    However, the connection is lower than the top of the toilet bowl and lower that the top of the bathroom sink bowl. The connection is made with a mission band.

    If there ever was a sewer backup, I want to avoid any water that might enter the vent stack past the connection of the two pipes.

    Is my plumber’s connection the correct way?

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    Plumber jimbo's Avatar
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    It can't be a horizontal connection. It could be done with a 45 degree wye, and the vent continuing up at 45

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    DIY Senior Member DanMcD's Avatar
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    It is a vertical vent connection from the crawl space up the bathroom wall to the roof.

    Attached is a picture of the toilet and vent connections under my crawl space.
    Name:  Toilet (left)  & Vent (right) Connections.jpg
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    DIY Senior Member DanMcD's Avatar
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    When one looks at the picture of my pipes in the crawl space, the PVC vent pipe is on the right. The picture shows it going straight up. At the top of the picture would be the bottom of my bathroom floor next to the wall. From the bottom of the floor in the bathroom, the PVC pipe goes straight up (vertical) until it is connected by a mission coupling to the cast iron pipe which then also goes vertical to the roof. The mission coupling connection is about 11 inches from the bathroom floor in the house, which is lower than the top of the toilet bowl. Both the PVC vent pipe and the cast iron vent pipe the PVC is connected is in the wall behind the bathroom toilet.

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    Forum Admin, Expert Plumber Terry's Avatar
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    If it's a mission with a metal wrap on it, you're good to go.

    Those mission couplings are designed to hold at least 10 feet of head.
    Last edited by Terry; 10-13-2012 at 10:44 AM.

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    DIY Senior Member DanMcD's Avatar
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    Thanks. I checked and it is a mission with a full metal wrap.

    Bye the way, was I right that, if the sewer did backed up, could water in the vent pipe reach the level of this couling since it it is about 7 inches lower than the top of the toilet bowl?
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    Last edited by Terry; 10-15-2012 at 10:44 AM.

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    Test, Don't Guess! cacher_chick's Avatar
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    You are thinking about this too hard.
    As long as the vent is vertical it is fine, even if the sewer backs up.
    If the vent were horizontal, then it would not drain, and that would be a problem.

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    Forum Admin, Expert Plumber Terry's Avatar
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    You can install a mission coupling anywhere you want. The couplings hold at least ten feet of head pressure.
    The vent from your toilet goes vertically straight up through the roof.

    Bye the way, was I right that, if the sewer did backed up, could water in the vent pipe reach the level of this couling since it it is about 7 inches lower than the top of the toilet bowl?
    That would be a concern if couplings leaked; which they don't.
    It is not a problem.
    Last edited by Terry; 10-15-2012 at 09:15 AM.

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    DIY Senior Member DanMcD's Avatar
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    Terry, Hj,

    The picture I posted was taken by my plumber and is the view in the crawl space. The vent pipe in the picture is on the right; the pipe to the toilet is the pipe on the left.

    All I can say is the new PCV vent pipe that you see in the picture continues straight up through the floor (which is about 3 inches thick), then it continues straight up and is connected by a mission band to the cast iron pipe at a point 8 inches above the bathroom floor. Both the PVC and the cast always run straight up. Both the cast, and the new PCV above the bathroom floor, run up the bathroom wall (wall is behind my toilet). The cast section goes all the way to the roof where it exits.

    The mission band has a full metal jacket.

    I do not know how to describe it more clearly.

    Dan

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    DIY Senior Member DanMcD's Avatar
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    Just meant all the vent pipes run vertical.

    The PVC and the cast are connected together at a point 8 inches higher than the bathroom floor...but lower than the toilet bowl top or the sink top.

    The plastic DOES NOT go through the roof.

    Bye the way, my plumber is a master plumber and says it is all OK.

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    DIY Senior Member kreemoweet's Avatar
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    I don't know what hj is on about, unless he is thinking that there's a DIFFERENT vent being connected behind your toilet. As it is, you could
    have a gosh-darn straight coupling connection in that vent pipe every foot, if ya wanted too. You keep mentioning your sink and sink vent,
    for some reason, but by your description that has nothing whatever to do with the pipes being discussed, and maybe that's confusing people.
    Also, I can't imagine why you would have any question at all about a sewer backup rising to the plastic-cast iron joint: of course it would, since
    there is no other route of exit from those pipes.

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    DIY Senior Member DanMcD's Avatar
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    I only mentioned the sink because, if the sewer backs up, I was just stating the obvious that the water level in the sink would be higher than the connection of the plastic-cast iron joint. Sorry about the confudion.

    You verified what I thought was the case when you said: "I can't imagine why you would have any question at all about a sewer backup rising to the plastic-cast iron joint: of course it would, since there is no other route of exit from those pipes. Thus, water could go higher in the vent pipe than the connection with the mission band (I thought this might not be safe).

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    Forum Admin, Expert Plumber Terry's Avatar
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    Wow!

    Things must be different in Arizona then on the West Coast.
    We use couplings on plumbing below 42" all the time. Wait...........is there a moderator here to help us out with this?

    UPC 705.1.8 Shielded Coupling Joints
    When piping systems are joined by means of shielded couplings, such couplings shall conform to approved standards and shall not be considered as slip joints.



    Your plumber did fine. It's time to cover up the work and finish the job.
    Last edited by Terry; 10-15-2012 at 09:16 AM.

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    Forum Admin, Expert Plumber Terry's Avatar
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    Just meant all the vent pipes run vertical.

    The PVC and the cast are connected together at a point 8 inches higher than the bathroom floor...but lower than the toilet bowl top or the sink top.
    The vent pipe is vertical from the crawl space all the wall through the roof according to the homeowner.
    There is no mention of a re-vent here or any horizontal vent piping.
    The vent starts in the crawl space as the top of a santee that is positioned in the vertical position, and arms over to the water closet.
    Last edited by Terry; 10-13-2012 at 03:43 PM.

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    DIY Senior Member DanMcD's Avatar
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    Adding to my "plethora of postings" is the long awaited photo from inside my bathroom.

    At the bottom you will see the white PVC (as it enters from my crawl space up the bathroom wall)....then you see the mission coupling....then you see the cast iron continuing up the wall and its way Name:  PVC to Cast Connection.jpg
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    Dan

    PS, I just noticed the pciture I've shown is in an upside down view for some reason.

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