What affects the cost of ducted air conditioning?

The unit is the biggest single item, and its size should come from a heat load assessment of your rooms. The Victorian Government's starting range is 1.1 to 1.4 kW of heating output for every 10 m² covered, depending on the home, and that spread shows why floor area alone isn't enough. Insulation, glazing, orientation and ceiling height all move the number.

Victorians use more energy for heating than cooling, and in Melbourne's west winter usually sets the size. An undersized unit struggles on still July mornings. An oversized one costs more to buy and connect, cycles on and off in mild weather and can leave summer air cool but clammy. Ask each installer how they arrived at their capacity.

Zoning lets you heat or cool parts of the house on their own, which the Victorian Government recommends for ducted systems. Each zone needs a motorised damper and a place on the controller, and a temperature sensor in each zone adds wiring and parts. Living and sleeping zones are a common start; an upstairs or a separate wing often needs more.

Every outlet needs a duct run, a cut-out and a diffuser, and every return air grille needs a large duct back to the unit. More rooms and longer runs mean more duct. A quote that looks low may simply have fewer outlets, so count them.

The indoor unit usually sits in the roof space, so the roof decides how hard the job is. A generous pitched roof with a good manhole is the easy case. A low pitch, a tight manhole, closely spaced trusses or a roof full of old insulation all add labour, and sometimes a larger access hole is needed to get the unit in.

Double-storey homes add a step. The unit sits in the roof over the upper floor, so ducts for downstairs rooms have to pass between floors, through a cupboard or inside a bulkhead. That's one reason some two-storey homes end up with two systems, or ducted upstairs and splits downstairs.

A replacement can reuse ducts if they're in good condition, sized for the new unit's airflow and properly insulated. Ducts should be insulated to at least R1.5 with sealed joints. Ducts that are crushed, torn, leaking or undersized cost you performance for years, so replacing them is often worth it.

Switching from gas ducted heating adds its own items: the old heater removed, the gas capped by a licensed gasfitter, the flue taken out and the roof made good. Ducts sized for gas heating may or may not suit reverse-cycle airflow and cooling, so have them assessed rather than assumed.

A ducted reverse-cycle unit draws a lot of power. It needs its own circuit and a lockable isolating switch next to the outdoor unit. If the switchboard has no room or still has old fuses, it may need work first, and main switchboard, consumer mains or meter box work is prescribed work that needs an independent inspection.

Many homes run ducted reverse-cycle on single-phase power. Three-phase makes sense for larger systems, some of which are only made in three-phase, and for homes adding other big loads such as EV charging. A home that already has three-phase has a wider choice of units.

Put quotes side by side and check they describe the same job. Different capacities, zone counts or outlet numbers make prices impossible to compare. Ask each installer to separate required work from optional extras and to list what's excluded, then get the full price in writing before work starts.

The electrical side of any install finishes with a Certificate of Electrical Safety, so ask who issues it and keep it with the system's paperwork.