G2 Gas Fitter Practice Exam

Which type of appliance mixes combustion products or flue gases with the medium being heated?

1. Indirect-fired appliance

2. Direct-fired appliance

3. Low-efficiency appliance

4. High-efficiency appliance

The correct answer is: Direct-fired appliance

The correct choice is the direct-fired appliance because it involves the burning of fuel directly within the appliance to produce heat. In this type of system, combustion products or flue gases are intentionally mixed with the medium being heated, such as air or water, which is then used for heating purposes. This direct interaction results in efficient heat transfer, as the heated gases are part of the process that increases the temperature of the heating medium. Indirect-fired appliances, on the other hand, usually utilize a heat exchanger where the combustion takes place separately from the medium being heated. This creates a barrier that prevents the combustion gases from directly mixing with the heated medium. Low-efficiency and high-efficiency appliances are terms that describe the performance of an appliance but do not specifically address how combustion gases interact with the heating medium. While high-efficiency appliances can minimize heat loss and improve performance, the core function of directly introducing combustion gases to the material being heated identifies direct-fired appliances as the answer to this question.