What line is insulated in an air-cooled split system with a furnace?

In an air-cooled split system with a furnace, the suction line is typically insulated to prevent the refrigerant inside from absorbing heat from the surrounding air. This is crucial because the suction line carries low-pressure refrigerant gas from the evaporator back to the compressor. Insulating the suction line helps maintain a low temperature within it, ensuring that the refrigerant remains in its gaseous state and enhances the overall efficiency of the system.

Insulation also minimizes any potential condensation that could form on the outside of the line if it were to be left uninsulated, which can lead to moisture issues within the building. In contrast, the discharge line, which carries high-pressure refrigerant gas from the compressor to the condenser, does not require insulation since it operates at a higher temperature. Similarly, the return line and supply line serve different purposes within the HVAC system and do not need insulation for the same reasons as the suction line.