how do cars bring in warm air from the engine without flooding the cab with any carbon monoxide? It has got to be all so close together, right?


how do cars bring in warm air from the engine without flooding the cab with any carbon monoxide? It has got to be all so close together, right?

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The carbon monoxide is inside the engine and tubing, routed to the exhaust. But the heat generated from the engine can be outside all of that, like how you can warm your hands from a filled mug without getting them wet with coffee.

Ventilation air is heated by a heat exchanger, a small radiator through which engine coolant circulates. The hot coolant warms the air as it passes from the ventilation intake under your windshield, through the heat exchanger, then to your car’s vents.

Some older cars heated air directly from the exhaust pipe, part of which flowed through its own heat exchanger.

A properly maintained exhaust system releases no exhaust gases until they reach the tail pipe, well clear of the engine bay.

There is a small radiator in the dash called a heater core, the ventilation system is routed around it. It basically sits in a box and air is blown through it to heat the air which comes out the vents of your car.

To add a bit of a tip for emergencies, if you find your engine overheating, blasting the heat will route the engine coolant thru the heater core and marginally drop the coolant temps.

Not going to magically save the day, but it will help a tiny amount in a pinch. Particularly if you’re stopped and the engine is at idle, rather than under load during driving.

Your car has a pump which circulates coolant (let’s just call it water for simplicity’s sake) through channels inside the walls of the engine. This water picks up heat from the engine and routes the (now hot) water through the radiator, where moving air cools the water so it can repeat its journey. This is a closed loop – no oil, fuel, outside air, or combustion byproducts should ever come in to contact with this water.

So now, your car’s engine also functions as a very effective water heater.

Well, at some point during this journey, the water circulates through a second small “radiator” which is usually located in a duct between your dash and engine, because this radiator has a fan which blows through it. This (now warm) air is what blows in to your cabin. This is also why most cars have to ‘warm up’ before the heater starts working – if the engine isn’t hot, it isn’t producing any hot water. This doesn’t apply to electric cars which use an entirely different system since there is no internal combustion engine generating heat as a byproduct.

The fresh air intake location for your AC/heater varies depending on model, but is usually located in an area where it is highly unlikely to suck exhaust from your own engine. I’ve seen them under the front passenger wheel well, for example. This doesn’t mean your car can’t suck in exhaust from other cars – this is possible. Typically there is a cabin air filter between you and the outside world, which helps in many cases. In any case, these incidental exhaust fumes aren’t as dangerous as they are annoying, which is why it’s often best to switch your climate control to “Recirculate” (those weird arrows) when you’re in dense traffic. In addition, your cabin will warm/cool faster in Recirculate Mode since it is processing already-conditioned air from inside the vehicle, rather than trying to heat/cool air at whatever temperature it is outside.