A line set is a pair of insulated copper tubes used to carry refrigerant between the indoor and outdoor units of an ACIq or MrCool system. The larger tube carries the low-pressure gas, while the smaller tube carries the high-pressure liquid. We offer a variety of lengths and sizes in our Installation Kits collection to fit any home layout. It is essential to use high-quality, pre-insulated line sets to prevent energy loss and "sweating" that could damage your walls or ceilings. For Ductless Mini Splits, the line set is often hidden behind Line Covers-Guards for a clean look. Proper Brazing or Flare Nut connections at the ends are the most important part of a leak-free installation. Choosing the correct diameter for your unit's tonnage is critical to maintaining the manufacturer's warranty and system performance. They are the "arteries and veins" of your home's cooling infrastructure.