Wall hung Toilet Cumulative Change in Direction and minimum to vent

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StevenJ

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Hello, I am looking to get some advice on water closet minimum lengths of trap arms and cumulative change in direction calculations for wall-hung toilets.

Q1: Are there minimum lengths required for water closet traps arms protected by vents as there are for other fixtures? Does the code I posted below 2.5.6.3(1) exclude wc with the statement: "(1) Except as provided in Sentences (2) and (3)..."
I ask because I am looking to vent my toilet using a 3x3x1.5 wye in the vertical above the floor and space is TIGHT! Based on my calculations I likely will be just short or at 3" min distance from waste to vent. *also my codes allow for 1.5" to vent a 3". it's in the table as the minimum.

Q2: Do we start counting degrees of change from the waste pipe outlet bend (piece of HDPE pipe provided, that is directly behind the wall hung toilet/wall) or start counting after this 90?
Based on the code below 2.5.6.3(2): "Do wall hung toilets ... also 'discharges vertically' and depends on siphonic action? If the answer is yes, then does the cumulative change in direction count after this vertical discharge?

Images below. Our building codes provide this:

OBC and NPC2020 2.5.6.3. Location of Vent Pipes

(1)
Except as provided in Sentences (2) and (3), vent pipes that protects a fixture trap shall be located so that
(a) the developed length of the trap arm is not less than twice the NPS of the fixture drain,
(b) the total fall of the trap arm is not greater than its inside diameter, and
(c) the trap arm does not have a cumulative change in direction of more than 135°.

(2) The trap arm of water closets, of S-trap standards or of any other fixture that also discharges vertically and depends on siphonic action for its proper function shall not have a cumulative change in direction of more than 225°.

(3) A vent pipe that protects a water closet or any other fixture that also depends on siphonic action for its proper functioning shall be located so that the distance between the connections of the fixture drain to the fixture and the vent pipe does not exceed
(a) 1 m in the vertical plane, and
(b) 3 m in the horizontal plane.

Thank you for you time!
 

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wwhitney

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A couple comments, without actually trying to answer the questions you posed:

1) You could get the wye a bit lower by using a street reducing wye.

2) I believe with a horizontal discharge toilet, the wall elbow is part of the S-trap that the toilet uses for its "siphonic action". So at least in theory it is possible that having the vent connection too high in the wall would defeat the intended siphonic action. What does the toilet installation manual say?

Cheers, Wayne
 

StevenJ

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Hi Wayne,

1) that's a good idea, i will look into it if needed.

2) According to the carrier and toilet manufacturer the wall elbow is not part of the toilet flush operation. These are washdown, gravity fed toilets and have no s-trap and no siphonic action. The toilet manufacturer mentioned to try and have "at least 4" from the vent and bowl connection. This could have a negative impact where the air is not properly forced out due to the short distance and thus resulting in slower draining."

Does this seems accurate? It's interesting that this isn't mentioned anywhere in the provided written instructions and no code specifies this. I guess I can attempt to ensure this minimum distance...
 
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