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Thread: 2" trap for tub/shower. Is it a good idea?

  1. #1

    Default 2" trap for tub/shower. Is it a good idea?

    I am replacing all my waste lines. I would lilke a 2" trap and arm off my tub/shower instead of the 1 1/2 inch. My assumption is that a larger trap and pipe means fewer hair clogs and better/faster drain.. The trap arm runs about 2 feet to the 2" vertical abs drain line. I would use an adapter above the trap to go from for the 1 1/2 inch drain from the tub.

    So I am wondering if this is bad as it will hurt the self cleaning action of the smaller diameter pipe. The tub shower is used mostly as a shower . I have read pros and cons regarding oversizing drains.

    If I could find a 2" tub shoe, I would use that too..

    Thanks in advance for your replies!

  2. #2
    Master Plumber nhmaster's Avatar
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    You can't go from 2" anything down to 1 1/2" EVER!

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    To paraphrase, you could only do this if the section from the trap to the connection to the main drain is 2" or larger, you can't throttle it down. Keep in mind, too, that tub drains are almost always 1.5", but adapting that to a 2" trap isn't hard. When I remodeled, I ended up putting the tub where the toilet connection used to be and then still went with a 1.5" trap, but it dumps immediately into a 4" line.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Illinois Licensed Plumber SewerRatz's Avatar
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    Here is a couple clips from the Illinois code. Bold added by me.

    Trap Size. The size of trap for a fixture shall comply with Appendix A: Table E for minimum size of traps. No trap shall be larger than the fixture drain to which it is connected or the drainage pipe into which it discharges.


    When a P-trap is used on a bath waste, it shall be directly below the tub overflow. The overflow shall be fastened to the tub by means other than the face plate.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    quote; Trap Size. The size of trap for a fixture shall comply with Appendix A: Table E for minimum size of traps. No trap shall be larger than the fixture drain to which it is connected or the drainage pipe into which it discharges.
    When a P-trap is used on a bath waste, it shall be directly below the tub overflow. The overflow shall be fastened to the tub by means other than the face plate.

    I have NEVER installed a 1 1/2" tub drain, always 2" with a 2" trap and a reducer on the trap inlet. Even when I worked in the Chicago area.
    FEW overflow fittings have an independent way of fastening it other than the face plate. So either hundreds of installations are being turned down, or the code is not being enforced.

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