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Old 11-11-2008, 09:21 PM   #1
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Sizing pipe for replumbing job


I'm in the middle of remodeling a bathroom of mine and from this bathroom i can get to almost all the plumbing in the house at the fixtures and toilets. anyways i already have a couple slow leaks in my basement so i was wanting to rip it all out and replace it. What i need to know is what the best size piping is for the job. It has 3/4 now that feeds both hot and cold side but it has 1/2 going to all the water fixtures. we have the cold water pipe feeding all the fixtures. its like one pipe with a bunch of T fittings in it going to each fixture if that helps at all. we have well water and seem to have a lot of pressure coming from the well to supply everything. what i want is great pressure. My wife i think wants it to be able to blow the paint off the walls when shes in the shower. I was thinking about going with 3/4 everywhere including the shower riser. were also going to install a whirlpool tub when we do this remodel what size pipe would be good for that? Also what would be the best pipe for this job? i was thinking about using plastic cpvc pipe like what you get at lowes and home depot. but on the other hand people are talking about this pex pipe but it seems expensive. Also what about a manifold? i've heard talk about this would that be a good way to go on this. they wanted to do that on my heating in my house but didn't. any info would be a big help i want to do this the week of thanksgiving. i figure a week will be enough to do my house its not very big.
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Old 11-11-2008, 10:39 PM   #2
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Sizing pipe for replumbing job


Lots of stuff here.

First off pex is wonderful. So easy to work with.

Putting a larger line into the any faucet is a waste of time. The choke point in the system is at the faucet which is easily handled by a 1/2" pipe.

Same with the whirlpool tub. You can put in a 3/4" line but the faucet will make it a waste of time.

There is a saying, if it ain't broke, don't fix it.
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Old 11-11-2008, 11:02 PM   #3
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Sizing pipe for replumbing job


what about the shower riser? would you go 3/4 there? or just stay 1/2 from the main up to the top? would it hurt to go to 3/4 to the fixtures? in my own thought it would put more volume in the line for the fixture not necessarily more water for more pressure.
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Old 11-11-2008, 11:49 PM   #4
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Sizing pipe for replumbing job


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what about the shower riser? would you go 3/4 there? or just stay 1/2 from the main up to the top? would it hurt to go to 3/4 to the fixtures? in my own thought it would put more volume in the line for the fixture not necessarily more water for more pressure.
The volume will be determined by the smallest opening in the system. A 1/2" pipe will put out more water than the fixtures can use. A 3/4" line will put more water to the fixture and the same amount of water will come out the faucet.

Bottom line is that you will have spent a lot of time, energy and money with no change in the flow of water.

Think of a one lane road. You want to get more cars through it. So you spend millions to build an 8 lane freeway that leads up to the one lane road. All you end up with is a jambed up freeway waiting for all those cars to get down the one lane road.
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Old 11-12-2008, 08:48 AM   #5
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Sizing pipe for replumbing job


I can't think of another fixture in the house that would benefit from 3/4" line other than possibly the whirlpool.

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...Same with the whirlpool tub. You can put in a 3/4" line but the faucet will make it a waste of time.
This would be correct if the OP had standard fill valves...if they are high flow it is not a waste...in fact preferred. For some MFG, there are high flow 1/2" and 3/4", size your supply line accordingly.
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Old 11-12-2008, 09:16 AM   #6
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Sizing pipe for replumbing job


I would run a 3/4 main trunk for the cold and branch off to each fixture with it's own 1/2" line. Then if somebody flushes a toilet while you are in the shower, you won't notice as much pressure drop. A 1/2 line for the hot. Try to avoid feeding more than one fixture from a branch. Avoid as many ells as possible. They rob pressure. Use full flow ball valves everywhere.
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Old 11-12-2008, 10:17 AM   #7
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Sizing pipe for replumbing job


well i think thats what i'll do is run 3/4 main and 1/2 to all my fixtures. what about the whirl pool though. does it need its own line? or does it feed off of the hot and cold coming to the fixture? i've never seen a whirlpool tubs plumbing thats why i'm asking.

Also what do you guys recommend for pipes? i wanted to stay away from copper. you recommend pex or cpvc? I see that the pex pipe has the push to connect fittings. has anyone had experience with these? do they leak or crack? they seem to make the job go a lot faster and a cleaner installation.

Last edited by thejudges69; 11-12-2008 at 10:22 AM. Reason: had to add info
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Old 11-12-2008, 10:23 AM   #8
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Sizing pipe for replumbing job


I run pex on everything except for solar hot water applications (because of the heat and pressure it will rupture).
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Old 11-12-2008, 11:41 AM   #9
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I like PEX with home runs...but that's just me.

I have used the wirsbo, and copper crimp, never push-on in a wall...only for emergencies and "non-permenant" applications. Some area codes will not allow them to be used in a wall. I purchased the copper crimp tool and it's not failed me yet. I dis-agree with the assessment of the push fittings being cleaner when you have a piece of pex with nothing showing but a crimp ring.

The WP doesn't NEED it's own line...but if you have high flow valves, it will suck the pressure and flow to all the other fixtures on that line. That can be minimized with the home run manifold...but not eliminated.
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Old 11-12-2008, 04:35 PM   #10
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Sizing pipe for replumbing job


I'm seeing that is comes down to having more water pressure. I don't know how you get that from well water. I believe your pressure is coming only from your storage tank, until the pump kicks in and you get pressure from the pump. For me, it took some time, moving from city water to well water, to get use to the difference in pressure, its definitly not the same. And I did have a plumber one time set my pump up so, yes I had more pressure but only because he set it so the pump came on as soon as you opened a faucet. Not good for the pump or your eclectric bill.
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Old 11-13-2008, 08:05 AM   #11
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For me, it took some time, moving from city water to well water, to get use to the difference in pressure, its definitly not the same. And I did have a plumber one time set my pump up so, yes I had more pressure but only because he set it so the pump came on as soon as you opened a faucet. Not good for the pump or your eclectric bill.
That doesn't sound good or right. I grew up with a well and the only time we had poor pressure was when the bladder in the pressure tank would develop a small leak...for a while we could pump it up, but ultimately it had to be replaced. We had every bit as much pressure as any rural water or city water system.
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Old 11-13-2008, 03:13 PM   #12
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Sizing pipe for replumbing job


I'm not sure of the spec's, only that at the time I had a well, the pressure was never as good as when I've been on city water. I had at the time, a 20/40 pressure switch, I believe I had a 30 gallon storage tank. I'm posting a link I found on line, I assume the pressure is not the same in all cities. I'm not trying to get off track of the op's question, I'm just not sure changing the pipe size will increase water pressure from a well, unless its a real small size pipe. not a plumber by any means.

http://www.usinspect.com/Wells/Pressure.asp
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Old 11-13-2008, 06:24 PM   #13
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see heres what i did. the bladder in my tank was only pumped up to like 10 lbs. its supposed to be set at 2 lbs under your cut in pressure. we drained the tank and pumped it up. it made a huge difference. we also raised the pressure switch to 60 psi max. it also helped. i know that my well is able to put out more then 60 lbs of pressure it doesn't have a problem meeting the pressure switches demands at any pressure, me and a plumber tried that. i just seems that if you went with 3/4 everywhere it would give you more volume therefore increasing the pressure. on the other hand if you have 1/2 in. to the fixtures it would also give mroe pressure because the 3/4 in line feeding it would be forcing the water out faster to replenish what you using. i'm just trying to get the best setup for my house. if i sell it i think that this will make a good selling feature as well. like i said my wife wants to be able to blow th paint off the walls haha.
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Old 11-14-2008, 06:55 AM   #14
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Sizing pipe for replumbing job


You can have any static pressure you like, but if the pipe size is restricting the flow, then the dynamic pressure will drop off faster. A larger pipe will deliver more water and lose less pressure than a small one. Two 45 degree bends will lose less pressure than one 90 degree bend. As water is pumped through a pipe it creates turbulence from friction along the pipe walls. The turbulence actually restricts the opening in the pipe. The more water you try to force through the pipe the larger the turbulence becomes and the more restricted the path of travel. That is why a larger pipe will maintain better pressure under the same amount of flow as a small pipe. Fittings generate a lot of turbulence and rob even more pressure. Big pipe, fewer fittings= more pressure at delivery.
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Old 11-14-2008, 08:46 AM   #15
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Two 45 degree bends will lose less pressure than one 90 degree bend.
This is one of my big reasons for using pex. You can get by without fittings which increases throughput.

I did a test once of 40 feet of 3/4" pex with 4 90's compared to 40 feet of 1/2" with no 90's and just curved the line to the same configuration as the 3/4".

We filled a 30 gallon barrel and timed how long it took.

While the 3/4" still beat out the 1/2" it was not by much. Fittings really restrict the flow.
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