How does a car rapidly warm up extremely cold air?



When driving during a bitter cold winter, the air coming inside is constantly warm and comfy. How does the car warm up the air so much and so rapidly?

In: Engineering

Engines get hot no matter the weather so the heater pulls air from the engine compartment. That’s also why it may take a couple of minutes to get hot air when you start up the car. The engine is still cold.

A car’s engine produces a shitload of heat. Something like 80% of the fuel’s energy directly becomes heat. All of that heat must be managed, by venting into the air. Heat exchangers have engine coolant pumped through them, and they have fans blowing over them. One such exchanger has air pumped past it before the air is blown into the cabin. So, it’s really just a heat exchanger with engine coolant that the air blows past.

A car’s heater is a radiator, it pumps very hot engine coolant through a small radiator with of pipes and hundreds of tiny fins, which makes the fins quickly get very hot. It then passes the cold air through the fins. The fins have a very high surface area, so they can heat air quickly as it passes over them.

[Here’s]( a picture of the inside. The tubes at the bottom are for coolant flow in and out.

The combustion engine loses around 33% of its energy production as heat loss. Meaning your engine is a natural heater for the car.

The heat is then transferred to the cars coolant lines to be sent to the radiator for natural cooling.

Your AC/Heater system takes some of this heat and sends it to your cabin. Since coolant lines are frequently close to hot coffee to boiling temps, it doesn’t take long for all this heat to start usefully warming up the rest of the car.

Note: It is faster to warmup the car by driving it than idling. Though, nobody would blame you for wanting a warm car in the warming before your commute.

Video Link for better understanding, [YouTube: How Stuff In My Car Works – How a Car Heater Works](

I get the feeling you have never driven a diesel engine in cold weather? Yeah sure, it gets hot, but it can take anytime from 30 minutes to an hour before the air inside the vehicle gets hot. A gasoline engine gets hot much quicker.

Car heaters use heat produced by the engine. Engines run very fast, so generate heat pretty quickly. Some cars even rev higher upon starting to warm the engine and then lower the RPMs. Typically, the air is cold at first, and newer cars will shut vents from the inside until the heat warms up a bit.

The engine creates a lot of heat, that heat is managed by the cooling system (radiator, water pump, thermostat, and hoses). The hot coolant is piped into a small box (hvac case) in the car where the heater core (small radiator) is housed. A fan blows air across the heater core, the air is then directed to the vents (dash, floor, defrost).