A heater core is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes serve to increase surface for heat transfer to air that is forced past them, by a fan, thereby heating the passenger compartment.

A heater core is a small radiator, located under the dashboard of the vehicle and consists of conductive aluminium or brass tubing with cooling fins to increase surface area. Hot coolant passing through the heater core gives off heat before returning to the engine cooling circuit.