How high must the ignition source of a water heater be elevated above the garage floor?

The correct answer is established by the requirement to minimize the risk of ignition of flammable vapors that can accumulate in garages. According to the International Residential Code, the ignition source of a water heater must be installed at least 18 inches above the garage floor. This measure prevents accidental ignition of gasoline or other flammable vapors that might be present at floor level.

The rationale behind this height requirement is that gasoline vapors are heavier than air and tend to settle close to the ground. By elevating the ignition source above this potential hazard zone, the chances of combustion are significantly reduced, thereby enhancing safety in residential settings where vehicles may be parked, and flammable substances are more likely to be present. Understanding this guideline is essential for proper installation and compliance with safety codes.