The link below has a pipe sizing chart you may find useful. Terry

: I am currently doing copper horizontal runs (underneath the house) to replace some remaining remnants of old gavanized pipes that are attached to 1/2" copper verticals. The water supply comes in by way of 3/4" copper running the length of one side of the house.

: Simple question: Should I use 3/4" pipe to tee off the existing 3/4" main for a run to the other side of the house (about 20 feet) and reduce to 1/2" when I get to the 1/2" vertical, or can I run 1/2" the entire distance.

• Water Hammer Information