Gas Fitter Practice Test

How far above the burner port must the center line of the flue outlet be for a revertible flue furnace with a natural draft burner?

1. At least 6" (150 mm)

2. Less than 12" (300 mm)

3. At least 12" (300 mm)

4. At least 24" (600 mm)

The correct answer is: At least 12" (300 mm)

The requirement for the center line of the flue outlet to be at least 12 inches (300 mm) above the burner port for a revertible flue furnace with a natural draft burner is grounded in safety and proper ventilation principles. This distance ensures that combustion gases are effectively exhausted from the appliance, preventing any backdraft that could allow harmful gases to enter the living space. Maintaining this specified height also helps promote efficient airflow and reduces the likelihood of condensation forming in the flue, which could lead to corrosion over time. Natural draft systems rely on the principle of buoyancy, where warmer, lighter air rises, so configuring the flue outlet at the correct height is crucial for maintaining the natural draft necessary for proper operation. Additionally, this height meets industry standards and building codes to ensure safety and effectiveness, aligning with practices intended to optimize the performance of gas-burning appliances.