How is the carburetor heated in a Cessna 172?

In a Cessna 172, the carburetor is heated through the use of exhaust heat in the carburetor air intake. This method is crucial for preventing carburetor icing, which can occur when moist air passes through the carburetor and cools rapidly, leading to ice formation. The exhaust heat is routed to the carburetor air intake, warming the incoming air and ensuring that it remains at a temperature that prevents icing. This design utilizes the heat generated by the engine's exhaust system, making it an efficient way to manage carburetor temperature and maintain engine performance, particularly in conditions favorable for icing.

The other methods mentioned, such as using an electric heater, circulating warm oil, or engine coolant circulation, are not part of the Cessna 172's carburetor heating system. The aircraft relies solely on the heat from the exhaust, as this method is well-suited for the operational environment of general aviation and simplifies the system without the need for additional components.