Sizing is the question every ducted quote hangs on, and it is the one most often answered with a rule of thumb that is wrong for the house in front of you. This page explains how we size ducted reverse-cycle systems for Melbourne homes, which systems go with which home size, why zoning changes the answer, and what each size costs installed.
The quick answer
For Melbourne homes we install 10.5kW to 12.5kW in Small homes, 14kW in Medium homes, 16kW to 18kW in Large homes and 20kW in Extra large homes. The exact size for your home depends on floor area, layout, ceiling height, insulation, glazing, orientation and how many zones you want to run at once, so we confirm it at a free in-home design rather than from square metres alone. Installed prices as at 5 November 2026 run from $8,990 (Small) to $13,490 (Extra large, premium brand), all with AirTouch 5 zoning.
The four home-size bands we use
We deliberately keep the bands broad. Two homes with the same floor area can need different systems depending on how open the plan is, how high the ceilings are, which way the glass faces and how many rooms will be running at the same time. The band tells you which systems are in play; the in-home design picks the one.
| Home size | Systems we install | Zones and outlets in the package | Installed from |
|---|---|---|---|
| Small | Midea 10.5kW, Daikin 12.5kW | AirTouch 5, 4 zones, 6 to 7 outlets | $8,990 |
| Medium | Midea 14kW, Daikin 14kW | AirTouch 5, 4 zones, 8 outlets | $9,490 |
| Large | Hisense 16kW, Daikin 18kW, Panasonic 18kW | AirTouch 5, up to 8 zones, 8 to 10 outlets | $9,900 |
| Extra large | Midea 20kW, Daikin 20kW (3-phase) | AirTouch 5, up to 8 zones, 10 outlets | $9,990 |
"Installed from" is the lowest-priced package in the band, after the VEU rebate when replacing an existing gas ducted heater, single storey (double storey add $500). Full prices for every package by home size are on our south-east Melbourne cost guide and the Specials page.
What actually decides the size
- Floor area of the rooms you want conditioned. Not the whole house: a garage, laundry or a rarely used room is usually left out, which lowers the load.
- Layout. Open-plan living with a kitchen and dining area in one space is a single large load; a home with the same area split into separate rooms behaves differently and zones better.
- Ceiling height. Higher ceilings mean more air to condition. Newer estate homes often have higher ceilings than homes built in the 1970s to 1990s, and the size reflects that.
- Insulation and glazing. Ceiling insulation, wall insulation and the amount and orientation of glass change how fast a room gains heat on a hot day and loses it on a cold night.
- Orientation and shading. West-facing glass with no shading is the single biggest afternoon load in a Melbourne summer.
- How many zones you run at once. This is the one most sizing calculators miss, and it is the reason we visit before we quote.
Why zoning changes the answer
With AirTouch 5, every zone has its own temperature sensor and can be switched on, off or set to a different temperature from the app or wall console. In practice most families run the living areas during the day and the bedrooms at night, and rarely everything at once. A system sized for the whole house running flat out is therefore larger than most homes ever use. When we size at the in-home design we ask how you actually live in the house, and that often lands one band lower than the floor area alone would suggest. The reverse is also true: a home that genuinely runs every room at once, such as one with several people working from home, needs the full capacity. Our zoning simulation page shows how zone-by-zone running works.
Oversizing and undersizing
An oversized ducted system is not a safe default. It costs more to buy, reaches the set temperature quickly and switches off, then on again, which is harder on the compressor, uses more power than steady running and controls humidity and temperature less evenly. An undersized system runs flat out on a 40-degree day and still does not get there, and on a 2-degree winter morning the same thing happens in reverse. The goal is a system matched to the real load with zoning doing the fine control, which is why we would rather measure than guess.
How the in-home design works
At a free in-home design we measure the rooms you want conditioned, check ceiling height, insulation and glazing, look at the roof space for the indoor unit and duct runs, check the power supply (single or 3-phase) and the position for the outdoor unit, and talk through how you use the house so the zones are set up the way you live. You get a fixed price before anything is booked. Our services page covers what happens on installation day.
Common questions
What size ducted air conditioner do I need for my house?
For Melbourne homes: 10.5kW to 12.5kW for Small homes, 14kW for Medium, 16kW to 18kW for Large and 20kW for Extra large. The exact size depends on floor area, layout, ceiling height, insulation, glazing, orientation and how many zones you run, so it is confirmed at a free in-home design.
Is it better to oversize?
No. An oversized system costs more, short-cycles and controls temperature and humidity less evenly; an undersized one cannot keep up on extreme days. Size to the real load and let zoning do the fine control.
Does zoning change what size I need?
Often by one band. If you rarely run every room at once, a smaller system can serve the home. That is why we size in person.
How many zones can a ducted system have?
AirTouch 5 supports up to 16. Our Small packages include 4 zones; Medium, Large and Extra large packages include up to 8, each with its own sensor. More than 8 needs an expansion board, priced separately.
Do I need 3-phase power for a 20kW system?
It depends on the unit. The Daikin 20kW we install is a 3-phase unit; we check your supply at the in-home design.
What does each size cost installed?
As at 5 November 2026: Small from $8,990, Medium from $9,490, Large from $9,900, Extra large from $9,990, with premium-brand options from $11,490 to $13,490. All include AirTouch 5 zoning and are after the VEU rebate when replacing a gas ducted heater, single storey.
About this guide
The size bands, systems and prices on this page are the ones HVAC Climate Solutions actually quotes from, taken from our live package pages (prices last updated 3 November 2026, honoured until 15 November 2026). AirTouch 5 zone limits are from the manufacturer's published specifications. The sizing factors are the ones our designers check at every in-home design; we have left out square-metre rules of thumb on purpose, because in our experience they are wrong as often as they are right.