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.
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