What is a safety requirement for a water heater or furnace installed in a garage?

For a water heater or furnace installed in a garage, having any source of ignition at least 18 inches above the floor is a critical safety requirement. This height helps to mitigate the risk of ignition from flammable vapors that may be present in a garage, such as gasoline or other fuels. When venting or combustion devices are located close to the floor, they can potentially ignite these vapors, leading to serious fire hazards. By ensuring that the source of ignition is elevated, the likelihood of igniting explosive vapors is significantly reduced, enhancing overall safety in a residential setting.

Other options may not align with standard safety practices or regulations. For instance, a retaining wall is not a common requirement for such installations, and the idea that these appliances are not allowed is inaccurate as they are frequently used in garages. Additionally, while proper door separation is important for safety, it is not a specific requirement that relates directly to the physical installation of the water heater or furnace itself.