BASIC WATER LINE QUESTION

[Michael Travis]

I am going to plumb the house I built soon. I will be running water lines to a on demand hot water heater, a steam generator, a shower, a tub and 2 sinks. My questions is it better to have one line for H and C that branches off via T connectors to all the above or use a manifold with a separate line running to each. Is there a difference in how each way would hold pressure in the line, meaning would one way keep more pressure in the line than the other way. Sorry for my lack of plumbing lingo I am a DIYer. Thanks for any help and or advice.

 

[Mikey]

Here's a good video outlining pros and cons of the manifold ("home-run") approach vs conventional plumbing:

 

[Diehard]

Well you'll always have some fluctuation of pressure whenever water is being used somewhere, in either system.
(The first system you mentioned is typically referred to as a trunk and branch system where the trunk line would generally be a 3/4" line and the branches would be the tee going to the individual demands.)
I think it's safe to say the manifold system would result with less pressure fluctuation at each point of demand. But it really amounts to pipe sizing for each flow and pipe length.

I think if I was going to do a new house system I would look at it different ways relative to cost and actual pressure losses with various scenarios. For example a 1" (or 3/4") line running the length of the basement with home runs to each demand from there. Or a combination of manifold and trunk/branch approach. And/or a number of manifolds located closer to points of demands.

The one location for a manifold system is not your best approach in all cases. Since I just watched that video above, I'm getting off the pressure concern. I wonder what the pressure loss rating is on that manifold in the video at the higher flows???

 

[wood4d]

you are probably having two wc , a dishwasher and a washing machine along with a kitchen sink also. In nj we run 1" pex (or 3/4 copper) to on demand wh and run 3/4 for 3 fixtures and branch that off to 1/2". Some houses are good with a manifold and some arent. A ranch is usually not a good choice while a smaller home with a basement might be. Both setups work well but the manifolds use a lot of piping. The video has a hwh connected with pex, we cant go all the way to the hwh. I quit watching when they had a commercial.

 

[Diehard]

I really don't think that guy should be making videos on most of the ones I've seen. He's really not familiar with much of the details he talks about.
One example of many was when he said that there are two weights of copper pipe, L & M. Where L was typically used for buried applications. They may have changed a few things but to the best of my knowledge type K roll copper was the required buried copper weight.
What he knows best is how to make money making videos about subjects he's not qualified in.

 

[Mikey]

I think if I was going to do a new house system I would look at it different ways relative to cost and actual pressure losses with various scenarios. For example a 1" (or 3/4") line running the length of the basement with home runs to each demand from there.

That's what I did in a house in Florida. Worked great, and allowed isolating individual rooms or fixtures as needed. Only problem arose when the house was inspected at time of sale. The inspector didn't like it, and said it had to be changed to a conventional trunk & branch. By that time I was 3000 miles away, and didn't have time to argue. I asked Mr Inspector if he knew of a local plumber who would do the job... of course he did, and for $2000 my problem went away.

 

[Diehard]

That's what I did in a house in Florida. Worked great, and allowed isolating individual rooms or fixtures as needed. Only problem arose when the house was inspected at time of sale. The inspector didn't like it, and said it had to be changed to a conventional trunk & branch. By that time I was 3000 miles away, and didn't have time to argue. I asked Mr Inspector if he knew of a local plumber who would do the job... of course he did, and for $2000 my problem went away.

WOW! They must do things differently in Washington.

 

[Michael Travis]

thanks for your replies, just to clarify, we are not going to have a dish washer or washing machine or whatever a wc is, what I outlines is what we will have. We do have a basement so I can run everything underneath. i HAVE ATTACHED a crude diagram to show my bathroom/kitchen layout along with the two waterline options. everything is pretty close the bathroom is 8' x 10'

 

[Diehard]

What's the "On demand Hot Water"? When I see that term I think off Instantaneous water heaters.

What's that steam generator and what kind of water flow demand are we talking.

I could easily look at a a couple of scenario of flows demands, through different size and lengths of pipe and the approximate effects on resulting pressure losses. But I suspect, unless you have potential for some high flow demands, your pressure fluctuations will be minimal when using 3/4" and 1/2" tubing sizes.

 

[wood4d]

a wc is a toilet

 

[Michael Travis]

no toilets, yes on demand water heater is instantaneous and the steam generator will use 3/8ths of a gallon every 20 minutes.
biggest demand will be shower while also using a faucet, Tub and steam generator will be used weekly at the most. I am thinking a 1/2" trunk and branch system would work best for me or would a 3/4" trunk with 1/2" branches be better? do fittings in the PEX system even exist for such a thing? (3/4 to 1/2)

Thanks for all your help

 

[Diehard]

I would go with the 3/4" trunk with 1/2" branches.
PEX sizes run a bit smaller than copper.
As a general reference I have attached a little spread sheet I put together showing pressure loss per foot of both copper and PEX. It's hard to say what the pressure loss would be for the PEX fittings since they get reduced in size except for the "Uponor ProPEX Expander Fittings".
The pressure loss values can give you an idea of your losses through different size and length pipe at various flows.
I don't know how much pressure you have to start with and how critical it may be to minimize the losses.
Just as an example...
First off you can assume approx. flows as mentioned in the plumbing codes.
Tub - 4 gpm
Shower - 2.5 gpm
Lav sink - 2.2 gpm
Kitchen sink - 2.2 gpm
So depending on your final pressure you could be looking at a combined flow of about 4.7 gpm for a sink and shower. So if the common pipe for that flow was a 1/2" PEX say 20 feet long plus assume an equivalent length of pipe for fittings or say another 10 feet. For a total of 30 feet.
Looking at the attached chart, 4.7 gpm through a 1/2" PEX is approx. 0.247 psi losses per foot x 30 feet = 7.41 psi pressure loss.
Now 4.7 gpm through a 3/4" PEX is approx. 0.0476 x 30 = 1.43 psi pressure loss. Big difference, particularly if you're going longer distances.

 

[Michael Travis]

thanks so much, cn you recommend a pump to move water from my holding tank to the pressure tank?

 

[Diehard]

thanks so much, cAn you recommend a pump to move water from my holding tank to the pressure tank?

I'd rather not, but you can likely get a recommendation in the
Pumps and Wells section.