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 Advice on Water line sizing for a 100' run?
Author: herynkc (OR)

I am renovating an old house that needed quite a bit of work. I am doing a complete redesign of the water lines as they are currently a maze of 100 year old galvanized pipe with assorted sections of CPVC here and there - a real horribly inefficient mess. I am going to upgrade my service line to at least a 1" supply (it is currently 1/2") andf then split the line into two distribution manifolds in the basement (one for hot via the water heater, and one for cold.) Each location in the house will have its own dedicated line coming back to the basement manifolds. All are home runs. I was planning on running 1/2 inch copper pipe on each of these dedicated lines. Most of the lines are shorter (25-50 foot), and my longest run up to the master bedroom/bathroom on the second floor is approximately a 100' run.

Anyone out there with thorough experience designing whole home plumbing systems know if I should size this 100' run up to a 3/4 inch line instead of 1/2 like all the others? Im thinking the friction in such a small diameter pipe over that long of a distance will put a damper on things. The master bath this line feeds will have a double shower, double sink, and a toilet. My whole system will be soldered copper pipe.

Thanks very much in advance!

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 Re: Advice on Water line sizing for a 100' run?
Author: packy (MA)

can't you locate the cold 1 inch manifold and the water heater with it's 1 inch manifold closer to the center of the building?
if you want to use copper for the individual feeds, remember each 90 deg fitting used will add to any restriction.
it's really hard to advise without being there.
you have quite a bit of demand from the one bath you describe..
don't forget you're gonna need some recirculation line/s for the hot water.

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 Re: Advice on Water line sizing for a 100' run?
Author: stuckinlodi (MO)

Another idea,,,
For that bedroom that has the long 100' run you might want to consider putting a 2nd water heater near it. That way you'd just need to run 1 cold water line to the area and you'd get hot water to the bathroom fast without having to use a recirc setup. If electric it wouldn't have to be a 220v power cable, you can change the elements in a water heater to slightly lower wattage ones (3000 or 3500 instead of 4500) and use normal 20amp breaker and 12gauge wire. The water heater water would still get as hot as whatever temp you set on its thermostat, would just a little extra time to get there.

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 Re: Advice on Water line sizing for a 100' run?
Author: herynkc (OR)

It really cant be moved much closer since the basement is only beneath a portion of the homes footprint. Perhaps 10' closer is possible if many things get reworked, but I dont think that will sufficiently change the situation. Id prefer to stay away from installing a re-circulation pump, the water heater will be tankless.

There would be 5 - 90 degree bends and 2 - 45 degree elbows. So using a 3/4 inch line wouldn't solve the issue?



Edited 1 times.

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 Re: Advice on Water line sizing for a 100' run?
Author: herynkc (OR)

stuckinlodi,

Well as in your suggestion, if I were to run only the cold line to the master bathroom then install an addition water heater at this bathroom, would a 3/4" cold line suffice at reducing resistance? Im really just trying to determine how big to size the pipe diameter on this run.

I dont think the water heater will have such an issue getting hot water only 100'. or am I mistaken?

thanks



Edited 1 times.

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 Re: Advice on Water line sizing for a 100' run?
Author: stuckinlodi (MO)

Since you said you were renovating an old house I was thinking of the possibility of adding the 2nd water heater on the same floor as the master bedroom and put it into an added closet or storage room during the renovation, would not take up a lot of space. But maybe you are talking about renovations to the plumbing only and not room remodeling/additions.

Anyway, tankless works for some applications, hopefully you've read up on the cons and they won't be a problem for your situation. Many people have had tankless installed and were disappointed. Not trying to rain on your plans, just want you to be informed before tackling a project with this much work and expense. Good luck!



Edited 2 times.

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 Re: Advice on Water line sizing for a 100' run?
Author: stuckinlodi (MO)

Well, 100' could seem fairly long to me in the morning waiting for hot water to arrive so I could wash my face. Even in a 50' or 60' house with the water heater at one end and the bathroom at the other end of the house the wait is annoying. That's why those point of use undercounter water heaters are popular.

I'd think 3/4 inch pipe going to the master bath, then branching with 1/2 inch to sink, toilet and tub/shower would be fine. I'd run it 3/4 inch all the way to the cold water inlet to the water heater, then the hot pipe from the water heater can be 1/2 inch. But it would be good to hear from the experienced plumbers here on that question, so stay tuned.

If you do install tankless for the house maybe you could re-purpose the old conventional water heater for the 2nd floor only.



Edited 1 times.

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 Re: Advice on Water line sizing for a 100' run?
Author: PlumberLoren (CA)

To advise you properly, I would need a drawing with dimensions showing how far it is from the meter to each fixture and the water heater. I would also need the city pressure at the hose bib where the water enters the home.

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 Re: Advice on Water line sizing for a 100' run?
Author: Don411 (NY)

Home runs are very expensive and largely unnecessary with copper. Best practice would be 3/4" mains to the master bath and then reduce to 1/2" to connect to each individual fixture. A small point-of-use water heater under the sink would give you some good hot water while you are waiting for hot water from the main water heater in the basement to get there.

Same to other parts of the house, run 3/4" trunks to the area and branch to 1/2" for each fixture.

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