G2 Gas Fitter Practice Exam

Which term describes the mixture of combustion products with the heated medium?

1. Indirect firing

2. Direct firing

3. Convection heating

4. Radiant heating

The correct answer is: Direct firing

The term that best describes the mixture of combustion products with the heated medium is direct firing. In direct firing systems, combustion products—such as gases resulting from burning fuel—are mixed with the medium being heated, often resulting in a more efficient heat transfer and higher temperatures. This method is commonly used in applications where immediate and effective heat is required, as the heated combustion gases come into direct contact with the substance that is being heated. In contrast, indirect firing involves heating a medium without direct contact with the combustion products, which is not what the question describes. Convection heating refers specifically to the transfer of heat through the movement of fluids or gases, which may occur both directly and indirectly. Radiant heating is a form of heat transfer that relies on infrared radiation rather than direct contact or convection. Thus, direct firing is the only term here that accurately captures the concept of mixing combustion products with the heated medium.