Heater hoses and pipes circulate engine coolant to the heater core, providing cabin heat. These components are constructed from reinforced rubber or plastic, engineered to withstand high temperatures, pressures, and chemical exposure from engine coolant. They connect the engine coolant outlets to the heater core and back to the engine or radiator, forming a closed-loop system. Variations include molded coolant pipes for precise routing and straight hoses connected with retaining springs. Proper sealing and burst resistance are critical performance characteristics for this category.