I am going to replumb my old house using PEX . I want to be sure to use the proper size pipe all the way from the street to the hot water heater an to the rest of the house. I am thinking the easiest way to not worry about big pressure drops in the hot and cold lines is to use 3/4" everywhere.

The easiest way is to ask your building code inspector what they require. City and county codes would likely require a permit. I'd run a 1" main into the heater and cold water supply. You can run a trunk line down the length of the house using 3/4 but taps for fixtures can be 1/2" unless you are planning a roman tub. We really need to know where you live, how many sq/ft is the home and how many bath and fixtures. This booklet should help you a bit but skip down to arounds page 13 to read the chatrs. http://www.huduser.org/portal/publications/pex_design_guide.pdf

Hi John

What particular PEX are you considering using? Viega Pex, for example, has a 3/4" PEX that is actually closer to 1/2" copper when you consider the fact that the fittings on 3/4" viega PEX fit INSIDE the tubing... ;)

Check out Ballenger's link and then post back with more info. O.K.

Mark