I'm planning on moving our hot water heater from its current location in our mudroom down to the basement, to live in what will become sort of a mechanical closet in the to-be-finished basement. My plan is to attempt to remove the existing PEX plumbing going to the water heater as close as possible to the nearest branch, but if that turns out to be difficult I'd like to cap off the old PEX just inside the wall.
If I end up doing this, it will leave two 10-foot runs of 3/4" PEX going vertically up that wall to a dead end. These segments will see no real flow, and I expect they will stay at least partially full of stagnant water. Is this a bad idea?