Start with the local property, not a generic BTU chart
Oudtshoorn’s drier Klein Karoo climate is a different problem from the humid coast. Strong sun, hot summer afternoons and dusty conditions put more emphasis on correct capacity, shaded outdoor placement where practical and filters that owners can reach and clean regularly.
High ceilings, deep verandas and older solid-wall homes can alter heat gain significantly. Guest accommodation may also need independent room controls rather than a single central setting.