[Peter76]

I am planning on repiping my house and was wondering about the correct pipe sizes, since the (crimped) pex pipes have a smaller ID.

The closest bathroom is about 10 feet from the manifold one story up (manifold is in the basement) and the furthest bathroom is about 50 feet from the manifold 2 stories up. In between you have the kitchen (1st floor) and the utility sink (basement) and washer (basement).

Now I was wondering if I can run all fixtures with 1/2" PEX or if the flow / water pressure will be too low in the 2nd bathroom, particularly. I want to keep the loss of hot water to a minimum, therefore I would like to go as small as possible. I could put a point of use tankless water heater in the 2nd floor bathroom, however, I would like to prevent this - unless it would take 2+ minutes to get warm water up there.