Which of the following is NOT a method used on reciprocating-engine aircraft to provide heated cabin air?

Turbocharged exhaust is not a method used to provide heated cabin air in reciprocating-engine aircraft. Typically, in these aircraft, cabin heating is achieved through systems that utilize heat generated from the engine's operation.

Exhaust shroud heat exchangers capture heat from the engine's exhaust and transfer it to the cabin air. This method is effective as it utilizes the high temperatures of the exhaust to warm incoming fresh air, which is then circulated in the cabin.

Combustion heaters, on the other hand, are specifically designed to produce heat by burning fuel, and they provide a reliable source of cabin heating independent of the engine operation. They are commonly used in colder climates or when more robust heating is necessary.

Electric heaters represent another common method, using electrical resistance to generate heat for the cabin. They are useful because they can provide immediate warmth regardless of engine operation, making them a practical option in various scenarios.

In contrast, turbocharged exhaust mainly involves the use of exhaust gases to improve engine performance; its purpose does not extend to heating cabin air. Thus, it is not considered a method for providing cabin heat in reciprocating-engine aircraft.