Gas fired water heaters located in attached garage not in a closed cabinet using garage air for combustion air. As I read the unit should not share combustion air with the garage. In my opinion it should be in a enclosed cabinet and appropriate combustion air chambers at the top and bottom of the enclosure. Let me know?? Texas
Unless Texas has some specific rule, this is a common installation. No issue with a gas water heater in the garage as long as it installed at the proper height.
I’d say at least 1/2 of the houses that have gas WH in the country have the water heater in the garage.
Very common installation.
The general rule is the heater should be 18" above the floor to not have low lying gas fumes for combustion air. But any air above 18" is OK.