3 or 4" PVC to 4" CI and more?

3 or 4" PVC to 4" CI and more? finished photos!

This is the main stack going out of my house. It looks to be 4" CI. I plan on redoing the rest of the house in PVC. At the same time I am going to low flow toilets. Total units in the house are: 2 toilets, 3 vanity's, clothing washer, dish washer, kitchen sink, and 2 showers. Should I use 3" or 4" PVC. I know if you go too big with not enough water clogs can from from solids not getting washed away.

Also when connecting the PVC to the CI should I cut the CI and use a band or can I find some thing that will attach the PVC to the top of that T with the old washer drain on it?

I plan moving the 2" line from the laundry room to a Y on the upper horizontal run. Should I extend the current line up to the vent stack so that utility sink is vented or can I just cap it off? I could also leave it as is. Though right now it is at a bout a 45 deg slope. I could also put a trap on it and use it for the furnace drain and plug the other hole. Thoughts?

At the other end of the house is where the bathroom and kitchen tie in. Right behind the toilet is an opening for the pipes to the up stairs and the vent to the roof. I have the option of doing it almost any way I want but I do need to conserve some space. I plan to run 2 3" lines up. One will be the vent the other will be the drain for the upstairs bath. I was going to have 2 y's and 45's in a line to get the pipes closer for the vertical run. One will exit the roof the other will make a 90 to the US bath. What order should I do? From the toilet to the first Y is 2 ft. Should the first Y be the vent or the US drain line? After that will be a Y for the kitchen and bath with a clean out.

Thank you for all your help.

main questions

I see from no responce that maybe I did not word the question right. My main concern is should I go 3" or 4" for the main drain? Cost and space are not a problem here. I just want to make sure I get the best drainage and I have heard that too big of drain pipe can be a problem. May be that was just the old 6" CI though. I have searched and found nothing.

The second problem is the connection to the old stack. Should I use a banded connector or is there a rubber donut that would work better?

The last guestion is the order of the vent and US drain. I plan on 3" vent and US drain even if I use 4" in the basment for the main bath and kitchen. My gut tells me I should do toilet, then main vent, then US drain.

FYI the US drain is going to get caped off 6 ft up for now. That bathroom is going to go in some other time.

Also I plan on having the bathroom vanity drain into the 3" vent stack as the other 3" drain line will not be vented at this time.

Thank you.

sizing

You must be 4" pipe from the 1st toilet.Into the building drain.
Check your local code.

I'm getting a little confused by what you are writing.

I would check local code first.
With UPC code, they allow up to three toilets on 3"
When I add the fourth, it has to be 4" on the main line.
Our building sewers are 4"
Every fixture must be vented,
Vents can be tied back together above the flood level of the fixtures served.
If you are cutting cast iron, sometimes you can snap or cut, and then used a banded coupling.
Sometimes, you can remove the existing pipe, and use a poured joint, or a rubber substitute for a poured joint for the connection.

wet vent

We used to be able to dump a lav and tub over w/c.Called a wet vent.
In 3" through the roof.Now we use boca code and things have changed.

Thanks guys. My question is would I be better off with 3" or 4" for the main lines? 3" would be much better to work with under the toilet. For the main horisontal portion will 3" or 4" be better? Considering there will only be 2 toilets. If you tell me that 4" will drain as good as 3" with low flow toilets then I will just do the main line in 4" I may still drop to 3" from the last Y to the toilet so I have space. Or if I can go 4" right to the toilet I will. The planed toilet is a Toto Aqua I think. It is the one piece unit with the covered base. I just dont want to have problems with solids left in the main horisontal run.

Thanks for the pic Terry, I have had that as a file on my desktop for a while. The plan for vents is the kitchen will get a 2" vent out the roof, the shower will get a 2" out the roof or tie back to the main vent in the attic depending on space. The main vent out the roof will be 3".

The second story, if and when it is added, will have a 3" line direct to the basment and a 2 or 3" vent (or vents depending on the lay out) out the roof. That is a later project and will be caped off for now.

You get better drain line carry with smaller 3" lines.

The Aquia is a two piece, though in the picture, it looks very much like a one.

GrumpyPlumber said:

Same in my state..3" up to 3 closets OR 48 fixture units vertical - 34 horizontal (stack), please...don't ask me to explain what fixture units are here...NOT like UPC where it's for both water & drainage, we use a seperate system called factor values for water sizing.
We still allow wet vents, have to be 2".

OK...I'll explain F.U.'s, usually works this way:
1-1/4" drain is 1
1-1/2" drain is 2
2" drain is 3
3" drain is 5 (except on certain exceptions, like a closet is 6, flushometer is 8)
(yes, 2-1/2" is 4...for all those 2-1/2" fixture drains you can think of)

TJBaudio...maybe you can understand why Terry says to check your local code, if your not from my state, this is hieroglyphics.

Click to expand...

I get 31 units for my house. So by your code I would be fine with 3", Another posibility is I could home run much of the pluming to the main stack and make it 4" Keep the toilet on 3" so it washes out with each flush. Maybe put the shower on that line to add extra water. I just dont want to worry about hair and poo clogs clogs. If 4" washes clean then I will go 4" If not then I will go 3"
I wish I could find the post that got me concerned about going too big with the main line.

Terry said:

You get better drain line carry with smaller 3" lines.

The Aquia is a two piece, though in the picture, it looks very much like a one.

Click to expand...

Thank you! that was the info I was looking for, and I knew I was not nuts! All in all it sounds like I am better off with the 3" My gut tells me to run a 4" vertical with a 2" run to the kitchen, and a 3" to the main bathroom
leave the 2" to the laundry alone. The only question now is do I run a different 3" for the US or just combine it with the main bath 3", both will be full baths.

Also the Aqua is the unit I was thinking of, it looks like it will be easy to clean! That is a big point in oure house!

It's good having an additional fixture washing a 3" line with just a toilet on it.

poked around on the WI gov web pages and found a PDF with the codes. 3" horisontal is 20 Drain units. My house is 12 right now and will hit 18 with the US bath so I can run 3" no problem. It also sounds like I will get better drain action with 3"

GrumpyPlumber said:

Exactly the right way to do it, like I said, my code would be hieroglyphics to your plumbers.

Click to expand...

When looking at your system VS wi system I thing they say the same thing just using a different number set. I am feeling better about the whole set up now too. I saved the PDF so I have some thing to show the inspector if he questions my set up.

So the set up is going to be 2 baths + laundry and the main vent on 3". The kitchen will be on a 2" direct to the vertical stack that heads out of the house, vented on its own with 2" vent.

Now some more questions.
If you look at my origonal Pic you will see
you can see the new laundry line headed up at a 45 deg. My plan is to cut it where it pases the bathroom line and y it in there. Then this 2" will still be there. Should I:
A- not do that and leave the laundry as is.
B- cap it
C- run it up above the 1st floor fixtures and use it as a vent for the utility sink?

Another though that has come up is we would like a floor drain in the bathroom. Some thing like a 1.5 or a 2" This would catch any over flows and we have pets and put the pet wattere in there. Right in that area is the shower drain and the toilet. Also in that area is the kitchen 2" line. My gut tells me to use the kitchen 2" as it will end up lower than the shower drain AND be seperate incase of a clog in the bathroom pluming. I could also home run it to the main stack. I would have easy access to the main vent and would tie it in above the fixtures. Thoughts on this?

Thank you!

Thank you all.

I was going to get this uploaded sooner but got very busy. Any way the final lay out was:

3" PVC horizontal. Shower and toilet near the end with a 2" vent up and tied to the main vent in the attic.

3" vent with lav on it mid way down.

3" line to the up stairs and caped at a convenient location to add onto in the future.

2" on the kitchen sink with its own run to the main out of the house and its own vent.

Comment from the inspector on the pluming (and electrical) after a very quick once over was "looks like your not skimping, it all passes"

Congarats looks good!

drains

Trying to follow your description gets mind boggling but the one thing you do not want to do is connect the air conditioner's drain to the plumbing system, even if it is just an open connection above a P trap.