What is the reason behind maximum length =4" for a p trap seal ?

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Mar 24th, 2021 6:26 am

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Mar 23rd, 2021 7:02 pm

CuriousC [OP]: Deal Addict; Jun 27, 2015; 2070 posts; 355 upvotes; East York, ON

Mar 23rd, 2021 7:02 pm

What is the reason behind maximum length =4" for a p trap seal ?

Based on multiple Google search results the maximum seems to be 4"
https://www.google.com/search?q=plumbin ... l%22+lengh
What is the law of physics that imposes this constraint ? What happens if you make it longer ?

Lots of crazy 💡

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Mar 23rd, 2021 7:27 pm

Red_Army: Deal Fanatic; Oct 15, 2007; 5233 posts; 2678 upvotes

Mar 23rd, 2021 7:27 pm

CuriousC wrote: ↑ Based on multiple Google search results the maximum seems to be 4"
https://www.google.com/search?q=plumbin ... l%22+lengh
What is the law of physics that imposes this constraint ? What happens if you make it longer ?

Canadian code , there is no maximum ,
but the theory behind it is if the trap is too deep, the water may flow through too fast which can lead to siphoning of the trap seal and debris buildup
/thread

Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide

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Mar 23rd, 2021 9:53 pm

CuriousC [OP]: Deal Addict; Jun 27, 2015; 2070 posts; 355 upvotes; East York, ON

Mar 23rd, 2021 9:53 pm

Thank you
Does this look ok to you

Lots of crazy 💡

Mar 23rd, 2021 9:56 pm

Red_Army: Deal Fanatic; Oct 15, 2007; 5233 posts; 2678 upvotes

Mar 23rd, 2021 9:56 pm

CuriousC wrote: ↑ Thank you
Does this look ok to you

Looks fine. Your trap seal is 2.5” there. You’re not measuring it properly

Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide

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Mar 23rd, 2021 11:04 pm

CuriousC [OP]: Deal Addict; Jun 27, 2015; 2070 posts; 355 upvotes; East York, ON

Mar 23rd, 2021 11:04 pm

Thank you I am trying to make room for the coupler that makes the transition from 2" to 1.5"
Interesting that the tub was OK with 1.5 but the shower needs 2"
the drain was OK with the tub and the shower so I kept is as it was (1.5") hence the need to make the transition

Lots of crazy 💡

Mar 24th, 2021 6:26 am

Red_Army: Deal Fanatic; Oct 15, 2007; 5233 posts; 2678 upvotes

Mar 24th, 2021 6:26 am

CuriousC wrote: ↑ Thank you I am trying to make room for the coupler that makes the transition from 2" to 1.5"
Interesting that the tub was OK with 1.5 but the shower needs 2"
the drain was OK with the tub and the shower so I kept is as it was (1.5") hence the need to make the transition

It’s because a shower has a lower threshold, and also code requires a 2” drain for any shower with more than 1 head/outlet

Everything has been said before, but since nobody listens we have to keep going back and beginning all over again. - Andre Gide

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