Mike, fluid velocity = 5.11 fps with 1" pipe = 12.5 gpm. The head calculation does not change for the hx based on data provided. You still need to calculate your pump head in the rest of the hx loop at 12 gpm, then add 1.2' of head for the hx to get your total pump head. The 15-58 will move 12 gpm on H at about 7' of head; on M at about 3' of head.
