Where 8 kW sits in the guides
Rinnai's buyers guide groups everything over 60 square metres as extra large and gives it 7.0 to 9.0 kW, so 8 kW is the middle of its top band. The CHOICE table that Solar Victoria reproduces gives smaller figures: 5 to 7 kW for 60 to 80 square metres, and 6 to 9 kW beyond that.
The gap between them is the room and the climate. ActronAir says tropical and subtropical areas ask much more of a system than cooler regions, and a well-insulated home needs less capacity than a poorly insulated one.
Heating a big room through a cold winter
In a cold climate, a big open space may need its 8 kW for heating rather than cooling. FairAir, from AIRAH, has a heating load estimator built on winter design conditions for 19 regions or cities. It leaves out heat from sunlight, appliances and people, and AIRAH still recommends a full load calculation by a contractor.
In Canberra, the ACT Government's guide suggests asking whether a split has an H2 rating, which it says means the unit will work efficiently through the Canberra winter.
One 8 kW split, or a system for the whole house?
| One large split | Multi-head | Ducted | |
|---|---|---|---|
| What it looks after | One open area, up to about 80 square metres | Several rooms from one outdoor unit | The whole house from one installation |
| Bedrooms | Each needs its own unit | An indoor unit in each room | A vent in each room |
| Zoning | Switch units on and off | Very good: unused rooms can be turned off | Limited to good, depending on the system |
| Efficiency (CoP, average to excellent) | 3.7 to 6.4 | 3.7 to 5.1 | 3.5 to 5.0 |
The rows come from the ACT Government's guide to reverse cycle systems. CoP (coefficient of performance) is how many units of heat a system moves for each unit of electricity. The same guide says splits suit houses below 180 square metres. Our split or ducted quiz asks the same questions in four steps.
What you can weigh up first
You can
- Measure the open space, try it in the size calculator, and list the other rooms you'd like comfortable.
- Note whether winter or summer is the harder season for you.
Leave to a licensed installer
- A heat load for the big room, and for the house if you're weighing ducted.
- Checking ceiling or underfloor space if ducted is on the table.
- Refrigerant work. A multi-head needs a full RAC01 licence holder, not the restricted RSS03.
What we'd do
What we'd do
If one space needs 8 kW and you'd also like the bedrooms comfortable, we wouldn't buy the big split until we'd seen what a multi-head or ducted system looks like for the whole house. If it really is the only space you use, a single 8 kW split is a sensible answer. Either way, we'd want a specialist in that system doing the job.
