G2 Gas Fitter Practice Exam

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

1. Direct fired appliance

2. Indirect fired appliance

3. Zero-crossing appliance

4. Self-contained appliance

The correct answer is: Indirect fired appliance

An indirect fired appliance is designed to heat a medium, such as water or air, without directly mixing combustion products (flue gases) with that medium. Instead, these appliances use a heat exchanger to transfer heat from the combustion process to the medium. This method ensures that the medium being heated remains free of contaminants that might be present in flue gases, such as carbon monoxide, particulates, and other combustion byproducts. This characteristic of indirect fired appliances is particularly important in applications where maintaining the purity and safety of the heated medium is crucial, such as in domestic hot water systems or commercial heating applications. In contrast, direct fired appliances involve a combustion chamber where the medium being heated is in direct contact with the flue gases, allowing for efficient heat transfer but also potential contamination. Other types mentioned do not pertain specifically to the mixing of flue gases with the heated medium to the same extent as direct and indirect fired appliances.