Is running 1/2" copper off the 3/4" going to adversely affect pressure?

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Bob3800

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We're adding a bathroom to the house, and a friend is chewing my ear off on this, so I'm hoping to find some closure here :)

Currently we have 1" to 3/4" copper throughout the attic. The plumber for the new bathroom is planning to come down with 3/4" from the attic, and then branch off with 1/2" for the shower, and sink+toilet respectively (shower has its own 1/2" runs, and the sink has its own 1/2" runs - cold shared with the toilet.).

Each 1/2" run is approximately 15' long.

My friend is advising that the plumber should make each run 3/4", or else we will lose pressure. Is there anything to this worth considering?

Thanks in advance!
 

Terry

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The lav and toilet can share a 1/2" line, and the 1/2" for the shower is good too.
I normally run a 3/4" line for cold and split it into two 1/2" lines.
I run a single 1/2" for the hot, lav and shower.
 

Bob3800

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Thanks Terry! It sounds like we have no issue at all then. Perfect.

The lav and shower have their own 1/2" runs, as the shower fixture is on an opposite wall. My friend mentioned the run being 15' would cause the issue... good thing I posted on here before mentioning it to the plumber. Haha

Thanks again. Much appreciated!
 

Reach4

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3/4 for hot would not be as good as 1/2, because it would increase the amount of time it would take for the hot water to arrive.
 

Jadnashua

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Unless your shower has multiple heads, or you have a deep soaking tub, 1/2" line is fine.

IF the distance from the WH is long, you might want to consider configuring things for hot water recirculation. Installed with a timer or on-demand activation, the delay to get hot will be very small and the convenience greater with less wasted water. Keep in mind, say it takes a minute to get hot if it hasn't been run in the shower (about the time it takes in my home), you're wasting 5g or so, diluting your WH with 5g of cold water that has to be reheated with no gain for you, and unless you're on a septic system, paying for sewer costs for it as well. If your lines are well insulated, the energy use to recirculate can end up less than without it and it does save sometimes precious water resources. The delay on a flow restricted faucet like a vanity sink will be greater, since it is limited to 2.5gpm, while a tub is unrestricted (but, a shower head is also 2.5gpm).
 
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