I am updating the cast iron plumbing in my old house to pvc... might as well as I am doing a down to the bones renovation. I am also converting an upstairs bedroom into a master half bath. The new bath will have it's own vent stack and will drain to the basement where it will cross the ceiling to the main stack. I had a friend who seems to know a lot about plumbing come by tonight and he said my vents are wet!@##$%^%^?? I guess I either shouldn't listen to him, get a second opinion or get an education. I am trying to understand the full function of the vent. My assumption... first and foremost to allow sewer gas to escape the house. Secondly, to keep the water from being siphoned out of the p traps in order to keep the gas from coming in through the drains. Right so far? So, where can I find diagrams on proper vent set up. What I am wandering is... how far from my shower p trap can my drain run horizontally before it reaches my dwv stack? He said after my p I needed to go into a t. Up of t goes into attic and over to T into vent... down from t 90's toward sewer stack. I wanted to just come out of my p to the sewer stack. Any links to venting diagrams of do's and don'ts would be appreciated as well.

You just got a piece of the vent concept. Take a pop bottle and cap it with your thumb and turn it up side down, now remove your thumb. This is how your drains would work if they did not have a vent. The vent has little to do with sewer gas other than it is full of sewer gas. The trap holds the gas inside the drain and vent. P traps don't easily siphon but old S traps could siphone so that's why they are prohibited by code. Did anyone tell you how much louder your drains will be after switching to PVC, quite a bit. Speedball1 will be here in the morning and he's the pro. He'll give you tons more info but likely has diagrams and pics for you.

OK princeton... let's see if I can help at all.

You are right so far ;)

The ptrap keeps the sewer gasses out of your house.

The vent system keeps the traps from siphoning and allows for turbulent flow of waste water, i.e. allows entire drainage system to be self scouring/cleaning in a manner of speaking.

There are many different kinds of waste/vent systems but for your purpose... we will discuss individual waste/vents and wet venting.. ok?

In some plumbing systems each fixture (toilet, tub, shower, sink, washing machine, kitchen sink, etc.) gets its own individual vent that connects into vent system and terminates out the roof. In other plumbing system, depending on distances and other critical information you can use an individual vent to WET VENT other fixtures... again, there are critical facts that need to be adhered to (such as lavatory vent can WET VENT toilet/tub but must be run full size 2" vent to its termination out roof or into larger pipe that goes out roof).

You asked specific question... how far from shower ptrap until reaches DWV waste stack... well, that is not as important as how far the SHOWER VENT is from the shower ptrap. It is all about FIXTURE TRAP to VENT distance in plumbing... for example, most showers require a 2" waste line/ptrap with a vent connected ABOVE CENTERLINE OF SHOWER WASTE LINE within 6 feet of the trap... that is run and connects so that it connects into the vent system at least six inches higher than the top of the lavatory sink... that make sense?

Anyway, a bit involved. First pic. Represents one way of presenting wet venting... but is not up to date.. fittings have changed.. and everything in the basement is just wrong (so ignore that)

Second pic. Represents wet venting... BUT the fittings are poorly presented.. and you will need to understand some principles before you finish.. ok?

Get back to me? I can probably do better. Or maybe speedball/ballenger/growler/doug238 have some better ones.

If this helped, please RATE THIS ANSWER. Thank you


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Thanks massplumber2008, The 2" shower drain within 6' of the vent info was cool. The diagrams are cool too. I am actually 6 1/2' from my wet wall with my shower p. So my friend was right that I would have to vent it through the wall surround on my shower and run the vent up into the attic above and over into my vent-stack. However, I still wander if I can connect a t in line of my drain line with the branch pointing up. This differs slightly from what he told me as he told me I would have to stand my t up and 90 my drain back to continue it's course to the soil stack. Any clue what I am saying? It's just a matter of how to install the t to connect the line coming from the p going to the vent and going to the soil stack. One way it stays in line, the other requires a 90 degree correction to continue it's course to the stack. Or could I get by with 6 1/2 foot to my stack? :rolleyes: Thanks again.

As a general rule I teach all apprentices to use wye fittings for anything to do with waste on horizontal pipes... even if waste on a wet vent fitting... reduces confusion for some. So, on horizontal pipe picking up lavatory drain (i.e. the tub wet vent as well) I would want you to use a wye fitting as I still treat the wet vent fitting as a drain fitting... and drain fittings hate short turns as in a tee fitting... that make sense?

AND... *looking around*... 6.5 feet to vent may work... but I did not say that.. OK? ANy chance you can get me a drawing of exactly what you are doing.. and the distances from all?

Get back to me.

If this helped please RATE THIS ANSWER. Thank you.

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I thought I would try to draw a diagram of my plumbing. The diagram is limited to the new installation area of my dwv system only. It is all open and in rough in and is subject to change. I would like any help I can get... so what's wrong with this picture

It dawned on me that my pipes labeled re-vent are actually supposed to be 1 1/2 inch.

Hi princeton... looking pretty good... but I do see some issues.

I am unclear on the drawing of the toilet piping... Does the toilet tie into the top of a double TY.. See if you can draw that a little clearer.. by chance.

You don't need 3" vent/waste line to sink...just need 2" if wet venting the toilet and then can get rid of the individual vent on sink as well. See if you can post the toilet piping better...

BUT if NO 3" vent out roof already then you do need the 3 inch vent...let me know if you already penetrate roof with an older vent....or if this is the first penetration through the roof.

And where are your dandy clean outs?? One belongs at base of the stack..another just as conects into the 4" main stack (which shows that you have a 4" vent out your roof...:p ..so don't need that 3")

Get back to me if you can with toilet piping drawn more clearly. Thank you

Tough to draw in 3d so I had to compensate for it by flattening things out a bit. Shouldn't affect it much. Really not understanding the concept of wet venting. Yes, I do have a 4 inch vent and a 3 inch vent already going through the roof. On other side of house... cannot tap into from here. I am going to stay around to try to get help this pm. THanks in advance.

OK... getting there... let me see if I can draw something up based on that.. I will post in about 1 hour.. ok?

Let's see if this helps.. let me know if any questions.

This is correct by uniform plumbing code accepted in Massachusetts.. should work there, too... I hope!

Sure appreciate this.

God Bless