Start with the local property, not a generic BTU chart
Bellville is a busy northern-suburbs centre with established family neighbourhoods, townhouses, medical rooms and small offices. Inland afternoon temperatures and west-facing windows can create concentrated heat gain even where the total floor area is modest.
Single-storey homes often allow efficient back-to-back installations; multi-unit complexes may need body-corporate consent and more deliberate condensate routing so neighbouring units are not affected.