Prem-I-Air EH1644 Manual page 3

Slot the 2 hook brackets over the upper 2 screws and tighten to secure to
the wall. See Fig 3.
Fix the two L-shaped brackets to the underside of the heater using the
12mm screws through the round hole in the bracket - the oval hole in the
bracket locates over the screw that fixes the case together approximately
95mm from the case side at the rear of the unit.
Hang the heater on the hook-brackets using the two 25mm slots.
Fig 3
The L-shaped brackets will now line up with the lower holes in the wall.
Attach to the wall using the other two 30mm screws. See Fig 4 below.
Fig 4