Any Hydraulic Experts here?

[PocketThunder]

I am putting an addition on my house.  I am adding two bathrooms upstairs and i need to size my water supply pipe correctly.  I have a 3/4" supply main from the city to my basement.  I need to go 81 feet from that point to the furthest fixture on the second floor.  My water pressure is 78 psi at the meter in the basement.  I have a total of 27 fixture units. 

So, according to my state plumbing code book i can go approx. 60 feet with 3/4" pipe, (but i need 81).  If i use 1" pipe i can go 250 feet.  So my question is, if i have a 3/4" main, then increase 1" pipe to the upstairs, and then back down to 3/4" (and then 1/2" at the fixtures) isnt the pressure going to be the same at both ends?

Do you follow?

[Rocky]

No, you need to change the main to 1".

[dkn1997]

I am no expert in household plumbing, but I have been repairing /building/plumbing swimming pools since 1988 and pipe size is a major issue.  the one thing I am sure of is that pipe size limits your volume, which, I feel, effects pressure. I use the garden hose analogy.  you turn down a spigot 1/2 way, and when you first press that nozzle, you get a real shot of water.  but hold it long enough and it dies down.  not enough volume.  the household pressure coming in has not changed, but the volume has changed since you cannot force enough water through that 1/2 closed spigot.

Even if you run the larger pipe between your meter and the fixtures, I doubt you will see an increase in pressure because it's already choked at the meter.  I could be wrong here, but that's what my experience tells me. 

I think that even using 3/4" all the way (which it sounds like they won't let you do) you would see the same pressure at the end.  from what I understand, a pipe of a certian diameter will only flow a certain amount of water, no matter how much pressure is supplying  it.  also, pressure is effected by volume.  the initial turning on the fixtures may result in a nice "rush" of water because of what's stored in the larger pipe, but once it's running, the small 3/4" street feed will only supply so much volume, even to the 1" pipe that's run in between.

Then again, do you really want to be taking your plumbing advice from a Pool Man?  I know I would not want to be a member of any club that would have me as a member.

[Paul G]

I just went and looked downstairs at my plumbing. This house is a split level built in 1997. The water feed comes in to the basement and runs all the way to the bathroom's on the second floor (like a two story). The house has a 1" main water line. It stays 1" all the way in to the hot water heater. There it tee's to a 3/4" line for both hot and cold water from that point on to the rest of the house. My second floor has great water pressure. I only have about 45 psi on this system. I am an electrician not a plumber, but I think if you ran 3/4" lines up to the bathroom it should be okay. If you have problems it would probably be that 3/4" main line. Maybe thats why I have a 1" main. If I remember correctly it cost me a little more per month because of that bigger line and associated meter. Check with your friendly local plumbing inspector for your town. Unless you just cant do that (if you know what I mean).

[PocketThunder]

Check with your friendly local plumbing inspector for your town. Unless you just cant do that (if you know what I mean).

  Oh ya i know what you mean.     But i'm doing a full second story addition on my one story house and i have all permits req'd, i wasnt gonna get away with this one.

No, you need to change the main to 1".

Rocky you are correct.  I called my inspector today and he said that they want the larger size 1" line run after the meter throughout the house for sufficient volume of water to the fixtures.  They agree that the pressure will be the same.  So, i have 3/4" at the meter, then i will go 1" to the upstairs, and then back down to 3/4" and then 1/2" at the fixtures.

My inspection is scheduled for tuesday so we'll see how i did on my design.  I tried calling some plumbing contractors and asked them if they would lay out the system for me but they would not do it.  They want the whole job and i dont have that kind of green..   The inspector did allow me to dry fit the system and then he would come look at it.  Then i can finish it all up and run the pressure test and he will come back and verify that.

Paul
in St. Paul

[Rocky]

Before I bought my house, all of my experience was with electrical.  i learned allot when I realized that the only hot water in my house was available in the kitchen sink.  It may seem like a pain in the ass, but the local building inspectors usually know what they are talking about.  Unless you are confident enough to challenge what they have to say, (you have to know your shit), they will usually point you in the right direction.  It is always better to err on the side of caution.  If you are doing the design yourself, then just allow for some extra time for corrections, and  think about the money you have saved by doing it yourself.  Personally, I saved about 5K by re-plumbing my house, and the satisfaction alone would have been worth it to me.

[Paul G]

That 3/4" line to the meter, and the 3/4" meter will be your biggest restriction. You should have a 1" main line to feed all the 3/4" lines to the system. Ideally it should be 1" all the way from the shutoff outside to a 1" meter to all the 3/4" runs. I am thinking that most everything will work well until you have a high demand for water, like two showers running along with a garden hose and someone flushes a toilet. Whats going to happen is that 3/4" line to the meter wont have the flow volume to feed the house with such high demand. Running a 1" line all the way upstairs wont really help much, wont hurt either. A 1" main line should feed all the 3/4" lines that go to the different areas of the house. At least thats how they did mine.
Really no point worrying about the outside plumbing until you have to. If you even have to. You my not have any problems with the 3/4" outside line since your pressure is good.