Washer 1.5" standpipe

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by traut27, Mar 1, 2019.

  1. traut27

    traut27 New Member

    Joined:
    Mar 1, 2019
    Location:
    Plymouth Meeting, PA
    My laundry room currently has a washer draining into utility sink. I am updating the laundry room and would prefer to have laundry drain to a stand pipe and not the sink. The sink connects to a 1.5" though and not 2" drain pipe. It has a 90 elbow and goes straight down into the concrete slab.

    1. Is my utility sink currently not vented? I don't see a vent pipe anywhere and don't see how one could hook into the drain pipe.

    2. Was considering attempting a 1.5" drain pipe with a AAV but hesitant since I'm not even sure how the sink is vented currently. Is this something that could potentially work?(I know 2" is needed for code)

    3. Is the only solution to drill up the concrete to see where the pipe goes and replace the 1.5" with 2"?

    I think the main drain pipe is under/in the concrete slab portion of my house and runs out toward the front of the house. In the picture the white rooms are the ones on top of the concrete slap :

    Layout.jpg

    IMG_20190227_200414611.jpg

    IMG_20190227_205608372.jpg
     
  2. Reach4

    Reach4 Well-Known Member

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    Sep 25, 2013
    Location:
    IL
    Your vent is in the wall above the sanitary tee shown in your second picture. [​IMG]

    Your inspector may be OK with something less drastic than #3. On the other hand, keeping what you have for the drain, is very functional.
     
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  4. Terry

    Terry Administrator Staff Member

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    They plumbed that without a vent. You should add an AAV there.
    In the 60's and before washers were drained with 1.5", so they have worked in the past. Sometimes I make the standpipe 2" and reduce down before the p-trap. You could always try plumbing it that way and then hooking things up to see how it works.
     
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  5. traut27

    traut27 New Member

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    If I were to try it would I use a single AAV or would I need one for the stand pipe and one for the sink?

    Option #1
    Option1.jpg

    Option #2
    Option2.jpg
     
    Michael Young likes this.
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    You should be aware that many of the newest, high efficiency washing machines tend to drain much faster than the older ones (most spin MUCH faster). They now require that washing machine line to be 2" for a reason. Your safest solution would be to still dump it into the sink if you can't upsize the pipe to the sewer to 2". It MIGHT work if you leave it 1.5", it might not.
     
  7. traut27

    traut27 New Member

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    Thanks for you input. All I'm looking for is might. I'm okay with plumbing it, testing it to the max and seeing if it works. Adding a new countertop and sink to the laundry room so I'd prefer not to drill holes in either in order to allow for draining into the sink. Also tired of cleaning the sink from the discharge. Laundry room gets used as our main entrance often so trying to clean it up. If it was in the basement or somewhere people didn't see all the time I'd just keep it in the sink.
     
  8. Terry

    Terry Administrator Staff Member

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    [​IMG]

    This one shows a sink and washer, both vented, but tied together at the top. One AAV would do this one.

    [​IMG]

    They make boxes with grills for installing in a wall.
     
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  9. traut27

    traut27 New Member

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    Awesome thanks for your help. Much Appreciated. Last question is if the height of the vent pipe that connects to the standpipe matters?

    DrainPipe.jpg
     
  10. Terry

    Terry Administrator Staff Member

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    Revents are 6" or higher above the flood level of the fixtures. We normally run them at 42" which is 6" higher than a kitchen counter.
     
  11. landsbergfan

    landsbergfan New Member

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    Does this method of reducing a 2" standpipe into a 1.5" trap offer less restriction than just a 1.5" standpipe? I thought to do this as well, but wasn't sure if I would actually be hurting myself.
     
  12. K-Man

    K-Man New Member

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    I am in a similar situation in my basement - I would think (common sense?) that necking down to 1-1/2" after the trap would tend to reduce the velocity and flow thru the trap and reduce the chance of siphoning. Actually restricting it before or after would reduce the velocity, but I would think that keeping a 2"trap is better off than a 1-1/2" trap. Wonder what Terrys take is on that?
     
  13. landsbergfan

    landsbergfan New Member

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    Reducing the pipe would actually increase the velocity, would decrease the overall flow rate though. I don’t like the idea of reducing while on a horizontal, so at the bottom of the standpipe before the trap was where I bought about putting it. I suppose I could do a bucket test
     
  14. Terry

    Terry Administrator Staff Member

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    In the 60's and earlier they had 1.5" for washers.
    My parents home before I remodeled that section of the home had that, and the overflows that went with it. I bought the home next door in the 70's and had a 1.5" with standpipe that worked for me. It can work, but if there is anyway to find the 2" that would be nice.
    What I have done with 1.5" and 1.5" traps has been to upsize the standpipe to 2" above the trap. Heck, you could even go 3" if needed. That gives you some buffer when the washer pumps out sort of like dumping into a laundry tray sink.
     
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  15. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    New England
    While today's high efficiency WM tend to use less water, they also tend to pump it out much faster. This is one reason why today's codes call for a 2" drain line.

    If you can access the rest of the line, upsize it to at least 2". A bigger diameter riser might help with the 1.5" line. What should work is dumping it into a laundry sink, and then maybe using a pump to evacuate the wastewater if the elevations don't work out. That would act like a huge buffer. If the pump fails, things get messy, though!
     
  16. Reach4

    Reach4 Well-Known Member

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    Location:
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    If you are to share the AAV, the horizontal vent pipe should be at least 6 inches above the entrance to the standpipe.

    If each trap arm had its own AAV, they each have to be at least 4 inches above the trap arm, 6 inches above insulation if any, and accessible for changing the AAV.
     
  17. K-Man

    K-Man New Member

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    Sep 23, 2019
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    LandsB

    Reducing below the trap reduces the velocity in the trap and above the trap. Yes it would increase the velocity (in 1-1/2 vs 2”) but not ABOVE the restriction.
    Put a 2” valve below a 2” trap (or 2” anything).
    Closed - zero Q, zero V
    Full open - full Q, full V
    Partially open- lower V, lower V
    i.e., a restriction downstream, reduces the flow and velocity upstream. (This is steady-state, it doesn’t take into account if there is a backup upstream, say in a standpipe, that increases the head above the trap).
     
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