Increasing Water Supply Line

[Zombie Hedgehog]

Hello,

I am having my basement finished and I want to address any existing problems with my house. My main water supply is from a 3/4 inch copper line, but transitions to 1/2 inch copper for the rest of the house. I'm finding that the static pressure is fine at about 40PSI, but drops once a few faucets are running. Would it make sense to replumb the main line to 3/4 copper or 1 inch PEX? I want to have this work completed before framing the downstairs walls since I will only have access to the water main. All of the plumbing will be accessible during construction.

The incoming supply is 3/4 inch copper to a 3/4 shut off, then shrinks to 1/2 copper to a 5/8 meter, then 1/2 copper to a backflow prevention valve. I'm probably looking to have the valve replaced, keeping the meter and existing plumbing. Having the meter upgraded to a 3/4 supply is probably out of my budget, but I'm open to ideas.

Thank you.

 

[Sylvan]

I would run 3/4" copper including the branches off the riser and then tee off to 1/2 Copper at the fixtures

Especially on the CW supply as more CW is used then HW

 

[Sponsor]

 

[Zombie Hedgehog]

I would run 3/4" copper including the branches off the riser and then tee off to 1/2 Copper at the fixtures

Especially on the CW supply as more CW is used then HW

How much of a restriction would the foot or so of 1/2 copper be at the start of the supply line?

 

[Sylvan]

It is not so much restriction it is a loss of volume.

Having a larger riser and branch line reducing at the fixtures will help protect against loss of volume when another fixture is used

Imagine taking a shower and someone tuns on a hose bib outside ... This is why so many people are scalded because their failed to install either a pressure or temperature balance shower valve

 

[Zombie Hedgehog]

It is not so much restriction it is a loss of volume.

Having a larger riser and branch line reducing at the fixtures will help protect against loss of volume when another fixture is used

Imagine taking a shower and someone tuns on a hose bib outside ... This is why so many people are scalded because their failed to install either a pressure or temperature balance shower valve

That makes sense. I know a lot more electrical theory than plumbing so I guess thats why this is confusing to me. Without getting too much into this, in general, how much does a restriction like this affect the total available flow (in GPM?) while retaining a similar PSI?

 

[Zombie Hedgehog]

Using the chart below and assuming about 10GPM flow to multiple fixtures, with a 1/2" pipe there would be a loss of 30psi/100 ft or 3psi/10ft or 0.3psi/1ft. So the 1ft section of 1/2" pipe would only see a roughly 0.3psi drop. But for 50ft to my hot water heater, then an additional 30ft back to my downstairs bathroom, thats a loss of about 24psi, leaving me with under 20psi of hot water to the shower.

With a 3/4" pipe, losses are about half at 15psi/100ft, which would mean a roughly 12psi drop to the shower for about 30psi vs 20psi using 1/2" pipe.

If the shower was only consuming 2.5gpm and no other fixtures were running, the final hot supply PSI over 80ft would be about 34psi with 1/2" pipe and 38psi with 3/4" pipe.

So from this, it would seem like having a small restriction would not heavily impact the total flow of water, but having an undersized pipe trying to supply all fixtures would result in a heavy pressure drop.

I would run 3/4" copper including the branches off the riser and then tee off to 1/2 Copper at the fixtures

Especially on the CW supply as more CW is used then HW

What do you think of using 1" PEX as the main CW supply to the water heater (transitioning to 3/4" copper to the heater), then using a 3/4" PEX HW supply leading to fixtures, connecting to the existing 1/2" copper fixture supplies and using 1/2" or 3/4" PEX for the new bathroom addition?

Any input would be great, thank you.

 

[Sylvan]

When I took a test for stationary engineer there was a bunch of electrical questions such as circular mill of a wire. left handed rule , Ohms law . ambient temperature and the NEC code

Plumbing is like electric a Diode is a check valve we have hot .cod and return electric has hot neutral and ground

The longer the length of wire the more resistance (friction losses) Increasing the wire size (pipe) allows for more electrons to flow

A single pole switch is a valve a diode is a check valve

Same theory just different materials

 

[Jadnashua]

IN copper the Copper INstitute's handbook calls for a maximum velocity of 5fps on hot water, and 8fps on cold. On a 1/2" line, for hot, that only equates to 4gpm. On a 3/4" line, it doubles to 8gpm. It's that radius-squared factor that make the big difference. Exceeding that value can literally erode the pipe from the inside, create water flow noises, and will decrease the dynamic pressure.