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1. Starting over basement plumbing

Hello everyone. I'm in the process of finishing my basement and I'm at the point where I'm at the plumbing. My water main is 1/2 copper.

I plan on using pex system, the compression ring method not expansion, with 2 manifolds for water distribution; one for cold and one for hot water. Where I'm getting a little scared is some people are telling me that the 1/2 pex system has a smaller ID then copper and it will effect my entire system flow.

Let me explain my sanity so you guys can let me know if I'm doing this wrong.

Idea 1 (before people told me about the ID): The plan of attack was, at the main, convert to 1/2 pex up to the pex manifold. The pex manifold has an inlet of 3/4 pex, so I would need to convert my 1/2 pex to 3/4 pex at the entry point. From there all my runs will be from the 1/2 pex outlets. I would also add a tee for my 1/2 inlet on the hot water tank and output 3/4 to the pex manifold.

Idea 2 (after thinking about the ID of pex): The new plan, convert at the main to 3/4 pex right up to the manifold. Then keep the 1/2 outlets as is for the runs. I would also add a tee of 3/4 for my hot water tank and output 3/4 to the pex manifold.

Any advice or even other methods would be appreciated.

2. What is the size of the water line coming from the street or well? If it is only 1/2", it will always be a restriction in the system.
Most single bath homes have a 3/4" main line with 1/2" branches to individual fixtures.

Plumbed with PEX, would be a 1" main line with 1/2" branches, or 3/4" if it is long or a high volume fixture like a shower with more than 1 head.

3. IF I used PEX, which I do not, I would only use 1/2" as the final connection to the individual fixtures, whether from a manifold or a main.

4. Its 1/2" from the city in a older home. 1 kitchen 2 bathrooms.

5. Then you won't be doing yourself any good until the supply line from the city supply is replaced. You can size the the inside piping as it should be, but the pipe coming to the house will restrict the flow.

6. It sounds like you need a new 1" water service.

7. Well at this point my supply line is 1/2 and im not looking to change it, that's why im trying to live with what I have now. That is why I am asking about if the 1/2 pex pipe will reduce the flow between the manifold and if I should go to 3/4.

8. There's no point in going to 3/4. Without increasing the main to 1" nothing you do will make much difference.

9. But wont my 1/2" pex line diminish my flow from my supply 1/2" copper because of the ID of the PEX? Im not trying to get more out of my 1/2" supply, just maintain the flow I have.

10. You should plumb the house as if you had the proper supply coming to it, because one day it might, and no one will want to have to redo the interior piping because it was undersized when you installed it.

11. You should plumb the house as if you had the proper supply coming to it, because one day it might, and no one will want to have to redo the interior piping because it was undersized when you installed it.
Yes. What ever is touched, should be done to current code. Sometimes it's done area by area.
If you added a large expansion tank near the manifold it would help a lot.

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