A water heater mounting structure for mounting a case to a mounting surface via a support fitting component that is fixed to the mounting surface in a vertical direction. The case houses a burning device. On a back plate of the case, a lock-engagement fitting component is mounted. The lock-engagement fitting component has an upper plate portion and a lower plate portion. The upper plate portion is fixed to the back plate, and the lower plate portion is lock-engageable with the support fitting component from above and has a dimension longer than the support fitting component in the left-right direction. The lower plate portion is lock-engaged with the support fitting component from above to hang and support the case through the lock-engagement fitting component by the support fitting component.