Heater hose connects LH upper heater valve to heater core. 1 per car. HVAC heater hoses are an important part of a vehicle’s climate control system. HVAC is an acronym that stands for heating, ventilation, air conditioning. HVAC heater hoses transfer engine heat in the form of engine coolant from the main engine cooling system to a heater core within the vehicle’s HVAC system. A heater fan then blows air through the heater core radiator where it is warmed and routed through the air vents of the vehicle. Like all heating system hoses, it is important to inspect HVAC hoses for wear and damage such as cracks or deformation. Following proper coolant service intervals will help to maximize the life of these parts.