A line set consists of two insulated copper tubes that carry refrigerant between the indoor and outdoor units. One line carries the high-pressure liquid, and the other carries the low-pressure gas. We offer high-quality line sets in various lengths in our installation kits. It is vital to use the correct size and to keep the lines insulated to prevent sweating and energy loss. To keep your installation looking clean, we recommend using a decorative line cover. Proper handling of the copper tubing is essential to avoid kinks that can restrict flow. They are the "arteries" of your entire heat pump system.