With this gas water heater being in its on little alcove supercede the 18" height requirement? The slab below is about 3 inches high.
More information would be needed to answer your question.
Generally, gas water heaters located in garages are required to be raised to at least 18" off of the garage floor. An “alcove” would not negate this requirement. The water heater would have to be completely isolated from the garage in order to be on the floor.
I was trying to attach a pic…but it won’t work…
18 inches above a garage floor w/ no exceptions…
“Click to Enlarge”
If it is a newer water heater and marked FVIR (flamable vapor ignition resistant) it can be on the floor.
If not marked this way than it needs to be raised
Water Heaters listed as FVIR are THE EXCEPTION
2003,IRC, 2408.2 Elevation of Ignition Sourse.
Exception: Elevation of the ignition source “IS NOT REQUIRED” for appliances that are listed as flammable vapor risistant and for installation without elevation.
The lowering of the FVIR Heater may also benefit venting, allowing a longer vent pipe that owers the chance of exhaust spill over.