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plumbing vent in frigid weather

cliffy | Posted in Construction Techniques on January 20, 2009 05:13am

I built a house for a friend of mine a few years ago that has its own septic tank and field bed.   We live in a a climate with about 5 months of winter so I like to go a little extra on the insulation. (R34 walls, R50 ceiling)  In this house the vent stack is in the exterior wall and projects close to two feet beyond the roof.

In the last couple of weeks we have had overnight temps in the range of about 35 degrees below freexing and the vent is icing up near the top.  I’ve built several houses with similar insulation and plumbing stategies that drain into municipal sewers, with no icing problems.

Thoughts?  Should I cut the stack closer to the roof?  Is this icing a sign that the septic tank is ready to be pumped?

Have a good day

Cliffy

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Replies

  1. plumbbill | Jan 20, 2009 05:47pm | #1

    In climates where icing is an issue we usually increase the vent two pipe sizes 1' below the roof.

    Icing on a vent in extreme cold could be caused by several things, most common is using hot water.

    Steam rises out the vent & freezes when it hits the open atmosphere.

     

    1. User avater
      BillHartmann | Jan 20, 2009 07:38pm | #3

      BTW, I was in a Lowes the other week getting some parts to install some vanity drains and saw something that I had never seen before.It was a cap for plumbing vent pipes.It was a mushroom shape and had 3 or 4 ribs on the inside. The ribs had steps in them so that it could fit different diameter pipes. And also spaced their off the pipe so that the space between the ribs was the clear space to vent.All of the vents that I have ever seen have just been pipes open to the sky..
      William the Geezer, the sequel to Billy the Kid - Shoe

      1. DanH | Jan 20, 2009 08:53pm | #4

        Any idea what purpose it would serve? Did it look like it could keep out critters?
        The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

        1. User avater
          BillHartmann | Jan 20, 2009 09:20pm | #5

          I was in a rush and did not look that closely, but think that it would keep out a squirrel..
          William the Geezer, the sequel to Billy the Kid - Shoe

          1. DanH | Jan 20, 2009 09:46pm | #6

            Or might just be a tasty snack for a squirrel, I suppose.Can you see yourself using them?
            The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

          2. User avater
            BillHartmann | Jan 20, 2009 09:47pm | #7

            No..
            William the Geezer, the sequel to Billy the Kid - Shoe

          3. wagmore | Jan 21, 2009 05:39am | #8

            I bought one of those mushrooms after we had our boiler serviced.  The tech found 2 squirrels in the combustion chamber.  The plumbing vent isn't too far from our chimney, so I was concerned about a squirrel getting in the vent.  Got a cap for the boiler flue too.

            The mushroom vent fit on perfectly and looked kind of cool instead of just a cut off pipe.  A few months later after winter set in, I was at the kitchen sink when the upstairs toilet was flushed.  There was a nasty sound of the water in the ptrap being sucked out.  I knew immediatly what it was.

            It really, really sucked getting up on the roof with snow and ice to chip off the mushroom cap.  The ice pattern on it was kind of cool, but it won't be installed again.

          4. DanH | Jan 21, 2009 05:41am | #9

            Yeah, I was figuring that something like that would make icing up more likely.
            The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

        2. fingersandtoes | Jan 21, 2009 08:14am | #10

          I've cleared a couple of vents that clogged with pine needles after a dozen years. I thought of putting a 90 on the top but it would look silly. A funny mushroom top might be just the ticket.

          1. DanH | Jan 21, 2009 03:35pm | #11

            Yeah, but if you've got funny mushrooms visible from the street you might get a visit from guys with the armor-plated vests.
            The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

    2. cliffy | Jan 21, 2009 04:49pm | #12

      The vent is 3 inches.  I have not had freezing that I know of in the other houses I built in a similar fashion so I'm thinking the prob is due to septic.

      Have a good day

      Cliffy

  2. DanH | Jan 20, 2009 06:43pm | #2

    The problem is that with a septic there is a lot of gas generated by the little beasties in the tank, so there's a lot more to vent than in a regular sewer setup.

    But so long as the gas generation is reasonably continuous (and it will be, for a septic) then the (relatively) warm air should keep the vent open, even though it may show ice on the outside.

    Two feet beyond the roof sounds a little much, though. The longer it is the cooler the gas gets inside, before it can exit. Being inside an outside wall doesn't help either -- not a good design.

    The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
    1. cliffy | Jan 21, 2009 04:57pm | #14

      The beasties in the tank was a theory I expected to be raised here.   The reason the vent is so long is that with the extra insulation on this house,  alot of snow sits on the roof.  We were originally concerned that the vent would be buried with snow.

      I don't know about the vent being a problem because it is in the out side wall. The wall is over 10 inches thick, the vent is 3 inches, and is located on the innermost part of the wall.  The closer the vent is to the lowest part of the roof the quicker it reaches the sky.  If it went up through an interior wall then through the attic it would have to travel 8 feet through a frigid attic.

      I will probably cut the vent down to 6 or so inches in spring.  I don't think the tank has been pumped since the house was built either, maybe that is not helping.

      Have a good day

      Cliffy 

      1. User avater
        Dreamcatcher | Jan 21, 2009 06:22pm | #18

        Easy way to find out if you really need your tank pumped...open the clean out (slowly) if water leaks out in the process you need a pump. I found out about mine when I was remodeling and had to tap into the main. Luckily, I had a rubber fitting to loosen. Once it started to leak I let it go figuring there was just a little residual water in the line. 3 hrs later it was still leaking and the whole house smelled like sewage. I tightened the clamp and called the pumpers. Good thing I didn't just hack into it with my sawzall!I can't figure out why your vent is freezing...do you live in a high wind area? My vent is very similar in placement to yours but is 3" copper. It never gets frosted...in fact, I have more of an ice dam problem as it melts the snow around it.DC

        1. cliffy | Jan 22, 2009 05:20pm | #29

          Good suggestion with the cleanout.  I guess you were just a couple of flushes away from totally full!  I don't live in a high wiund area but the house in this thread is.  It is windy as hell, at the end of a long farm field.   have a good day

          Cliffy

      2. wane | Jan 21, 2009 09:04pm | #22

        "The wall is over 10 inches thick, the vent is 3 inches, and is located on the innermost part of the wall."

        had this issue before, sounds like you've done everything right, if our vents are in an outside wall they must be on the warm side of the vb, I now put them in the middle of the stud bay so they are warm 3 sides, away from the stud,  definitely don't add a cap, it will make it freeze over faster, worst case scenario add a vent at the bottom and top of the stud bay to let the room air circulate over the pipe ..

      3. seeyou | Jan 22, 2009 12:13pm | #24

        If it went up through an interior wall then through the attic it would have to travel 8 feet through a frigid attic.

        I'm guessing the problem may be that the pipe is staying too warm. Instead of condensing on the inside of a cool pipe, most of the water vapor is making it all the way to the top before cooling enough to condense and then flash freezing. http://www.quittintime.com/      View Image        

        1. cliffy | Jan 22, 2009 05:25pm | #31

          Sounds logical.  The pipe only goes through about 17 inches of attic and is surrounde by blown in insulation.  I'm leaning toward the cut.  Funny thing is I've doe several homes and reno's this way and the only problem has been the house on septic tank.

          Have a good day

          Cliffy

    2. User avater
      EricPaulson | Jan 21, 2009 07:14pm | #19

      We have whole house traps here so nothing would be going back up the house vent.

      I've heard many regions don't require them. I can't imagine. 

      1. DanH | Jan 21, 2009 07:20pm | #20

        If you have whole house trap then you'd need a separate vent somewhere for the septic system.
        The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

        1. User avater
          EricPaulson | Jan 21, 2009 07:35pm | #21

          Trap is vented seperately and usually just above the trap and through the wall. Not sure it's still done that way though.

          All the appliance vents tie into the house stack(s).

            

      2. cliffy | Jan 22, 2009 05:21pm | #30

        We don't require whole house traps, but evey fixture does.  I've only seen them in various magazines.

        Have a good day

        Cliffy

        1. User avater
          EricPaulson | Jan 22, 2009 06:12pm | #32

          We have both. 

  3. Nails | Jan 21, 2009 04:57pm | #13

    cliffy........Just a side note .......You're driving through a subdivision passing a $250,000.00 house with white pvc pipes sticking out all over the roof , they never appear on the front elevation of the plan.

    Have you or anyone else seen any treatment that makes them blend or at least easier on the eye? Maybe it's just me , but I bet you will notice them more now that I have mentioned them.

    1. cliffy | Jan 21, 2009 04:59pm | #15

      Interesting observation.  I try to make sure the vents (plumbing and roof) are at the back.  The other one I hate is the electrical wires overhead, especially when there is a transmission pole at the lot line. The gas meter at the front is another classic.

      Have a good day

      Cliffy

      1. Nails | Jan 21, 2009 05:38pm | #16

        Cliffy.....electrial wires, local company's will trench for a $1.10 a foot , not a lot of money. I think the gas company and landscapers have cut a deal among them selves.

        While I'm on this rant .........many times I will be doing a punch list on move in day and the owners will get friends and family to help them move in and sometimes I just stand there and add to the punch list.

        A lot of money spent on the house and none spent onprofessional movers. Really , I don't know anyone who likes to help someone move in.

        Have the best day you ever had!

        1. cliffy | Jan 22, 2009 05:18pm | #28

          I went to the small expense of doing my electrical underground but I rented a truck and had two friends help me move!  But then again I'm in this house 12 years now and not quite finished.  The move cost me the truck, two pizzas and a few beer for supper.   Of course the wife and her mom supervised everything!

          Haver a good day

          Cliffy

           

    2. DanH | Jan 21, 2009 05:43pm | #17

      Lead boot.
      The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith

    3. User avater
      jonblakemore | Jan 22, 2009 06:32am | #23

      "Have you or anyone else seen any treatment that makes them blend or at least easier on the eye?"

      We just spray paint them roughly the color of the shingles. They don't disappear, but they're a lot less obtrusive. 

      Jon Blakemore RappahannockINC.com Fredericksburg, VA

  4. IronHelix | Jan 22, 2009 04:44pm | #25

    You do live in a cold climate, but I think the following still applies...

       Minimum Main Stack Diameter  4"

       Minimum Ht. above roof 5"

       Maximum Ht. above roof 12"

    Check your local code for additional info pertinate to your climate/location.

    Note: Dome caps may keep out critters or debris, but the moist warm air condenses on the inside and the drops freeze at the bottom edge drip line, accumulate and quickly freeze shut the stack.

    FWIW.....Iron Helix

    1. rich1 | Jan 22, 2009 04:52pm | #26

      Our code is 3" main stack, terminating as close to the roof as possible.

    2. cliffy | Jan 22, 2009 05:14pm | #27

      The 4 inch definitely does not apply but I'll look up the other two.  The house was inspected for plumbing twice.  OUr building inspectors who inspect plumbing are former plumbers.      I think I'll go with the trimming of the stacks height.   I did a house in the summer of 08 that is also on a tank and septic field, I better keep an eye on that one too.

      Have a good day

      Cliffy

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