How do I find out piping size for Trane XR series heat pumps 410A? I was wondering if there is a piping size and length chart available. I have a 3 ton system with a 3/4" suction line. The builder ran 7/8" to the outside and 3/4" to the air handler. I'm not sure where the reduction in pipe size happens. The unit is in a second story attic, so it would be quite the eye sore to run line set covers down the wall.