Furnace placement in a garage

The bottom of the furnace has the brains, about 18" up is the burner. Is this incorrect? or does the whole cabinet need to be installed 18" up?

How about an On Demand hot water heater, does it need to be 18" up as well? Both are Propane.

Thanks,

as I understand it Scott the burner assemblies have to be 18" off the floor

Yes. Source of ignition raised 18".

Works for me, thank you both.