Vent on a 90 up stream on horizontal?

[FishingDave]

Replumbing a bathtub, the vent is up stream 3in from a wye on its side to the bathtub trap. Is it okay to plumb it this way again.the original 1950 was setup this way and the 90 was all clogged up , the pipe didnt have much pitch. I don't have much room really tight there.

 

[wwhitney]

No, a dry vent has to come off on the vertical (at least 45 degrees above level), not the horizontal. Maybe a picture would allow us to suggest an allowable configuration.

Cheers, Wayne

 

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[Jeff H Young]

one of the worst ways to vent , , if the vent was coming off the wye side and was rolled up on a 45 it might be legal under some codes but generaly avoided . your plumbing is not legal so Id like to see it legal but at the least as I described would be a repair but not really a repair but compromise and will likely be trouble free replace that old cruddy section with new fittings and good slope maybe a clean out on the vent in the wall above. If remodeling Try to get it 100 percent right though

 

[FishingDave]

can i swap out the 90 with a wye tee ? or place sanitee on a 45 with a street 45 connected to the vent? or do i have to move the vent connection some how further down pass the wye? I am restricted for space 16" center 2x8 2" pipe so it really crowed.

 

[wwhitney]

Your tub trap arm can horizontally enter the side port of a san-tee, where the top and bottom are 45 degrees off plumb. Then a 45 on the top to get a plumb vent, and a 45 on the bottom to turn the drain either horizontal or vertical as desired.

There are other options too, a picture would help.

Cheers, Wayne

 

[wwhitney]

I am restricted for space 16" center 2x8 2" pipe so it really crowed.

Old 2x8s that are 7-1/2" or taller? That would let you drill a 2-1/2" hole and you could squeeze a 2" pipe (2-3/8" OD) through there. With a modern 2x8 that's 7-1/4" or 7-1/8", the allowable hole size is too small to run a 2" pipe through the joist. So while I'm generally in favor of 2" pipe for a tub, this may be a case where 1-1/2" makes more sense.

If you use 1-1/2", then the net drop for the centerline of a horizontal pipe that hits the side entry on a san-tee rotated 45 degrees off plumb and then a street 45 to go back horizontal is 2-1/2"+ (may vary a little depending on ABS vs PVC). For 2" fittings it's 3-1/8"+.

Cheers, Wayne

 

[FishingDave]

Here's the old layout. The circular hole is where the 2" vent is dropping down the wal

 

[wwhitney]

OK, so if the hole through the subfloor for the vent can be moved to the right (in the picture) within the wall, that would make things easier, but here's the basic approach for your situation, I think. I marked up your picture with some assumptions:

The red lines are the wall above, the tub valve wall. The blue circles are the tub drain (towards the bottom of the picture) and tub overflow, connected by the blue line. Then the left-right blue line hitting the overflow is the u-bend of the trap below the waste-overflow tee. The line coming off that that at a 45 is the elbow of the trap (that joint swivels to any direction). Then the next fitting is a wye, where the wye is rolled up 45 degrees from horizontal; the green branch is the vent, which has to rise.

So the geometric question is whether this all fits without the trap being too low and without the vent rising into the subfloor before it gets under the wall. Also the footprint of the vent won't actually run parallel to the joists as drawn, since you've rolled the wye up 45 degrees from horizontal; it will angle back towards the trap a little. That means you may need to put the wye a little farther downstream if you need to hit your existing hole with the vent, which would then require more height gain for the somewhat longer distance the vent needs to run before hitting the wall above.

Note that with the wye rolled 45 degrees above horizontal, you would need a 60 degree bend to turn the vent to true vertical. So the rising vent segment is actually only 30 degrees above horizontal, which isn't quite considered vertical, but is much better than actually being horizontal as in your original install, and is generally considered sufficient.

Cheers, Wayne

 

[FishingDave]

Wayne , you got it right on the money . Wish i could move vent to the right but it will be in way of the shower valve . Where the vent ( green line ) connects to the the trap ( blue line) not sure if i will have enough room for a wye but a tee on a 45 might work . What do you think of that? ill mock up some fittings tomorrow and take a pic to show you what fits . Thanks!

 

[wwhitney]

Since you are in CT, and subject to the IPC, then a san-tee on its back is allowed for a vent takeoff, and should be rolled at least 45 degrees above horizontal. So if that lines up easier/closer than a wye, that's fine. A wye or a combo is otherwise a better choice.

Cheers, Wayne