[gtojohn]

Insulating the larger suction line can be good, it would help losses during both heating and cooling modes. If you use you heat pump for cooling I wouldn't insulate the liquid line because during cooling mode you want to lose as much of the compressor's heat as possible to assist in subcooling the refrigerant. If you use it for heat only I would insulate the line set and all piping you can to prevent heat loss.