A fuel fired warm air heater is installed in a residential garage. There is no protection from vehicle impact. The ignition source of the heater must have a minimum ground clearance of ____________.

• A. 12"
• B. 18"
• C. 24"
• D. 36"

Answer: (B)

In a garage without vehicle protection, ignition sources for fuel-fired heaters must be raised above the floor to reduce the chance of igniting floor-level gasoline vapors and to lessen the risk from vehicle impacts. Elevating the ignition source creates a safe buffer where flammable vapors are less likely to reach an ignition point and where a vehicle bump is less likely to strike the burner or its controls. The standard minimum height for this setup is 18 inches, which provides adequate protection without being unnecessarily tall. A lower clearance like 12 inches would leave the ignition source too close to potential vapors, while higher clearances such as 24 or 36 inches exceed the minimum requirement for this scenario.