G2 Gas Fitter Practice Exam

Which type of appliance does not mix combustion products or flue gases with the medium being heated?

1. Indirect-fired appliance

2. Direct-fired appliance

3. Condensing appliance

4. Non-condensing appliance

The correct answer is: Indirect-fired appliance

An indirect-fired appliance does not mix combustion products or flue gases with the medium being heated because it uses a heat exchanger to transfer heat from the combustion process to the medium. This design ensures that the heated fluid, such as water or air, remains separate from the gases produced during combustion. This separation is important for safety and efficiency; it prevents contamination of the medium and reduces the risk of harmful emissions being introduced into the space being heated. The heat exchanger allows for effective heat transfer while maintaining this necessary separation. On the other hand, direct-fired appliances mix combustion gases directly with the heated medium, such as in a furnace, where the combustion of fuel takes place within the same environment as the air or water being heated. Condensing and non-condensing appliances can also involve direct mixing of combustion products with the medium, particularly in their operations and efficiencies concerning waste heat and flue gases.