Does a water heater or furnace in a garage have to be raised off the floor?
Yes — any appliance with an ignition source installed in a garage must have that ignition source at least 18 inches above the floor (IRC M1307.3).
Because gasoline and other flammable vapors are heavier than air and pool near the floor, the IRC requires appliances that have an ignition source (such as a pilot light or burner) to be elevated so the ignition source sits no less than 18 inches above the garage floor.
Appliances installed in a garage must also be protected from vehicle impact, typically with bollards or by locating them out of the path of a car (IRC M1307.3.1).
The same 18-inch elevation rule appears for gas appliances in the fuel-gas provisions (IRC G2408.2). Some listed flammable-vapor-ignition-resistant water heaters are addressed by their listing, but the elevation requirement is the baseline.
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Need this scoped to your jurisdiction?
Adopted edition and local amendments vary by city and county. Ask Donnie checks your jurisdiction and cites the exact adopted section.
Ask Donnie →General information based on the International Residential Code (a model code). This is AI assistance to verify — not legal advice. Confirm the adopted edition and any local amendments with your local building department (AHJ) and a licensed professional before you build.