Pipe size when adding bathroom?

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mc510

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Previous owner of my house added a second bathroom, with permits. They did not, apparently, re-do the original plumbing (which looks to be 5/8 copper) but just tapped-in with ½ inch copper to go to the new bath. I'm guessing that this is the reason that the shower temp (either one) goes off wildly if any other water is turned on. Or is what they did proper? (It's an older home and does not have pressure balanced shower valves, but probably needs them.)
 

Terry

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You can run two fixtures on 1/2"

pipe_size_2.jpg


pipe_size_1.jpg
 
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mc510

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Thanks for pointing me to those "fixtures" tables; good information!

Most common way we experience this is running the shower in the original bathroom, 5/8" (or maybe it's 3/4") copper piped. Then turn on the shower in the added bath (1/2" copper piped) and the temperature drops in the original shower. No other fixtures in use. Eight hot fixtures in total, but only four on the 1/2" branch.

Also happens when only running fixtures on the original size of the house. Running original shower, then turn on kitchen sink hot water = temperature drop in the shower. In this case, 5.5 hot fixtures on 5/8 or 3/4 diameter pipe; that shouldn't be a problem but is.
 

Terry

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1/2" copper is 5/8" OD
3/4 copper is 7/8" OD

1/2" PEX is 5/8" OD, and a smaller ID than copper.
3/4" PEX is 7/8" OD, and a smaller ID than copper.
 

Dj2

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Just to clarify:

ID = inside diameter.
OD = outside diameter.
 
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