Melbourne demands both heating and cooling, sometimes within the same week. Winters are cold and damp, summer northerlies push days past forty, and the old answer was ducted gas heating and evaporative cooling.
Plenty of older houses still run that setup, while newer estates in Wyndham and Melton are increasingly all-electric with reverse-cycle systems. Victorian energy upgrade programs have offered discounts on some efficient replacements, and customers ask about them, so pages should point to the official source.
Gas work needs a licensed gasfitter and is overseen by Victoria's plumbing and gas regulators. Refrigerant work needs an ARC licence, and electrical wiring needs a registered electrician, so credentials matter to careful buyers.