How a Car Heater Coil Works

The heater coil, or heater core, on your car, is like a small radiator. It’s the source for the heat in the passenger compartment of your vehicle.

Cooling System

The coolant that’s intended to keep your engine at a good operating temperature must become hot. When it is it’s directed away from the engine by the water pump. At this point the coolant will be around 200 degrees Fahrenheit, which is close to water’s boiling point.

Heater Coil

The hot coolant is directed into the heater coil. This is located by the firewall that separates the engine compartment from the passenger compartment. It’s very similar in design to a radiator. There are fins and tubes on the heater coil. These are intended to cool the liquid before it returns to the engine. However, as it passes through the heater coil it’s still amply warm enough to give heat.


As the coolant circulates in the heater coil, the fan blows the hot air into the passenger area of the vehicle. There is a constant floor of hot coolant into the heater core as the cooler liquid is pushed out. This means the passengers in your vehicle can remain at a steady temperature.