Lennox Compact Pro Installation Operating & Maintenance Manual page 10

Next, drill the holes for anchoring the fastening brackets to the wall
using as a first option the 4 holes on the ends of the bracket as
shown on the drilling template (see fig. 6).
If the wall is not very solid, it is advisable to use some extra
anchor bolts.
As you can see, the bracket can be fastened in a number of
different ways and positions. The air conditioner is heavier
on the left-hand side, so it is best to make sure of a solid
anchorage on that side. The anchor bolts provided require holes
with a diameter of 10 mm. In any case, the wall should be
inspected carefully to determine the best possible anchorage and
type of bolts suitable for particular situations.
Warning: The manufacturer is not liable in case of
underestimation of the structural consistency of the
anchorage made at the time of installation. We
therefore recommend that you perform this operation with
the maximum care as, if not done properly, it can cause
serious damage to persons and property.
When installing models equipped with heating pump, if no
drainage well for condensate has been provided built into the
wall (see paragraph 2.3.2), it will be necessary, to allow for
drainage of the condensate, to drill a hole through the wall
measuring 16 mm in diameter in the position shown on the
template (see fig.6).