What Size copper should I use?

Hi, I have been reading alot of "what size is best" but I have been getting mix reviews. I am re-doing all my plumbing, since I have the old PB, and it started leaking from the joints.
First, my house has basement(where my feed and HW Tank is) and 2 floors. I have 3 full bathroom, and 1 powder room, 2 kitchen, and 1 laundry.
My main water supply is 3/4" to the house and I am getting 75-80PSI. I am planning to run the CW with 3/4" and run 1/2" T at each fixtures. For HW I am planning to run 3/4" most of the way then run 1/2" T since my HW Tank intake is 1/2"... and it leaves the tank 1/2" also. So rest of the HW line will be 1/2" through out the house... (or... should I run 3/4" just like CW???)
I am planning to upgrade my water tank since 40L is not enough, and maybe I could get a tank with 3/4" feed and out.
Thanks in advance

One problem with 3/4" hot water lines is that when there is a long distance between the water heater and the point of use, it wastes mega amounts of water purging the cool water from that line. You might not think that the difference would be that much between 1/2" and 3/4", but it really is. One solutions would be to install a recirculation pump, but that requires a return line as well as the pump. Although that give you virtually instant hot water, with copper so expensive now, you might not want to do that. I think you should also keep in mind that you rarely, if ever, will fill all of the bath tubs, washing machine, etc. at one time, and new low flow toilets don't tax a water supply very much. I think 1/2" would be quite enough. I would suggest you consider a pressure regulator valve on the incoming water supply along with a thermal expansion tank. Your water pressure is excessive and that can take a toll on fixtures, supply hoses, and appliances. 60 to 65 PSI is plenty of pressure. If you have hose bibs outside, they would be in line prior to the PRV so you would still have full pressure on your hoses.

Most codes only allow two fixtures on a 1/2" line.

https://terrylove.com/watersize.htm

Thanks for your reply
I guess I will be using 1/2" for HW all around the house, and 3/4" for CW? I do see the point 3/4" will wast lot of water before HW comes out, and I don't really want to wast energy...
And from what Terry was saying/link, I added up and I have 34 fixture units so I should be using 3/4" CW line until it T's off to fixtures.
Would it make a difference if I use 3/4" in the basement for HW and use 1/2" T going up to main and 2nd floor? (for future, when I get a new HW tank?)
Again thanks for pointing and helping me out. (I will go get pressure regulator)

3/4" pipe is fine for a one bath home, but not for a two or three bath home.
A four bath home needs some 1-1/4" pipe.

If you are over 80 PSI, then you need a PRV,
At any rate, you should have some 1" pipe in there and make sure your 3/4" branches don't have over 19 fixture units.
https://terrylove.com/watersize.htm

is it ok to branch 3/4" to 1"(small to big?) My HW Tank feed & out is 1/2". Would I not get the same water flow from going 3/4" to 1", but have same water pressure?

This is a fantastic post because it is considering some issues I have never thought about before. I do not however see how a 1/2" line can only have two fixtures but a 3/4" branch can have 19 fixture units? Do we really mean a 1/2 inch line can only have 6 fixture units?

I have a 1/2 inch line in my basement feeding: a kitchen sink, a dishwasher, a washer, a utility sink and a garden faucet. Should I increase this line to 3/4" and branch off to 1/2"?

how a 1/2" line can only have two fixtures but a 3/4" branch can have 19 fixture units? Do we really mean a 1/2 inch line can only have 6 fixture units?

Click to expand...

I thought it sounded confusing when I wrote it.
Fixture units are measurements.
Plumbing fixtures are items.

A toilet plumbing fixture, requires 2.5 fixture units.

Most plumbers run only two plumbing fixtures on a 1/2" line
A toilet is 2.5 fixture units in the UPC code book
and the bath tub is 4.0 fixture units
Add those together and you have 6.5 fixture units.
The middle of the UPC chart says 6.0 fixture units on 1/2" pipes.
When you add the lav for the bathroom, you are at 7.5 fixture units.

A standard one-bath home with kitchen sink, dishwasher, water heater, clothes-washer, 1.6 tank toilet, lavatory, tub/shower combo and two hose bibs would be counted as 18 fixture units. That would need 3/4" pipe coming into the home.

Most standard three bath homes consisting of kitchen sink, dishwasher, water heater, clothes-washer, three 1.6 tank toilet, four lavatories, two showers, one tub/shower combo, one whirlpool bath and two hose bibs would be counted as 34 fixture units. Meaning a 3/4" water meter and a 1" main from the water meter.
https://terrylove.com/watersize.htm