Every fall, there is one morning I will wake up and get ready to come to the shop. I walk out to my car and realize…ITS COLD!  I run back in the house, rummage through my closet and find my jacket. Sad because the last dregs of summer are gone, but energized by the crisp morning air.

I finally get in my car and turn on the heat. A couple minutes later I am toasty warm and on the road. Have you ever wondered, “How does the heater in my car work?”

You are in the right place. Lets dive in.

Your vehicle has a heater box. In that heater box is a cooling element (called an evaporator core) and a heating element, called a heater core. The heater box passes air by these elements depending on your preference. If you want AC it passes air by the evaporator core, if you want heat, it forces air past the heater core.

What is your heater core? It is not electric (in most vehicles). Actually it resembles a small radiator. Like the radiator, coolant/antifreeze passes through fins of the heater core. As the vehicle heats up, coolant starts getting hot and your heater starts kicking out hot air.

How does the coolant get hot? That is an interesting answer. Your engine heats up the coolant. The combustion process of the engine creates thousands of small explosions every minute. Those explosions are very hot. To keep your engine cool, coolant is passed next to the cylinders (where those explosions are happening) and moves that heat away to your radiator and your HEATER CORE.

It takes a few minutes for your engine to heat up, that is why it takes a few minutes for your heater to start working.


At an auto shop, we solve problems. If your heater is not working, there could be several reasons. Maybe you have a coolant leak. Maybe your heater core is clogged. Maybe your heater box is not moving the air correctly past the heater core.

If your heater is not working, call our shop right away. It could be a symptom of a problem that might can be repaired easily now, but would cost thousands if ignored.

Have a great fall!