Heating and cooling calculator
Every way of heating and cooling an Australian house, costed for your floor area, your insulation, your climate and your state's prices. The results show what each system conditions as well as what it costs, because the cheapest options are partly cheap for doing less.
Your house
Your energy rates — change any of them
These are New South Wales’s published reference rates. They are a starting point, not what you necessarily pay — put the numbers from your own bill in and every figure on this site changes with them.
The usage rate on your bill, sometimes called the peak or anytime rate.
The separate cheaper rate an electric hot water tank runs on overnight, if you have one.
The fixed daily charge you pay before using anything.
Gas is billed by the megajoule, not the kilowatt hour.
Paid every day the connection exists, whether you burn anything or not.
Saved in this browser and nowhere else. No account, no email, nothing sent to a server.
Every system, side by side
Heating and cooling split out, so you can see which half of the year is costing you. In most of Australia it is the heating column, by a long way.
| System | Conditions | Heating | Cooling | Per year | Installed | 10-year total |
|---|---|---|---|---|---|---|
| Single split system | One main living area | $160 | $143 | $363 | $2,600 | $6,232 |
| Multi-split system | Most of the house | $369 | $331 | $820 | $8,500 | $16,703 |
| Ducted reverse cycle | The whole house | $521 | $468 | $1,188 | $15,500 | $27,381 |
| Ceiling fans | Cools only — you would still need something for winter. | |||||
| Ducted evaporative cooling | Cools only — you would still need something for winter. | |||||
| Electric panel or fan heater | Heats only — you would still need something for summer. | |||||
| Gas space heater | Heats only — you would still need something for summer. | |||||
| Ducted gas heating | Heats only — you would still need something for summer. | |||||
Assumes a 160 m² home, built before 2005, or no insulation upgrade, in the Sydney climate — 478 heating and 683 cooling degree days, against Melbourne's 1,239 and 173. Electricity at 33.1c/kWh, gas at 2.72c/MJ. The "conditions" column matters: a system that heats one room is cheaper than one that heats the house, and that is not the same thing as being more efficient.
Where each number comes from
Single split system — $363 a year
One indoor head in the room you use most. The cheapest way to condition a living area and, per square metre conditioned, the most efficient thing on this list — because it does the least.
| Conditions | One main living area |
| Heat it has to deliver | 1834 kWh a year |
| Coefficient of performance | 3.80 at 3.5 stars |
| Electricity for heating | 483 kWh |
| Cooling it has to deliver | 1647 kWh a year |
| Energy efficiency ratio | 3.80 |
| Electricity for cooling | 433 kWh |
| Servicing | $60 a year |
| Total | $363 a year |
Multi-split system — $820 a year
Several indoor heads on one outdoor unit. Conditions most of the house without ducts, and lets you heat one room rather than all of them, which is where most of the saving against ducted comes from.
| Conditions | Most of the house |
| Heat it has to deliver | 3901 kWh a year |
| Coefficient of performance | 3.50 at 3 stars |
| Electricity for heating | 1115 kWh |
| Cooling it has to deliver | 3504 kWh a year |
| Energy efficiency ratio | 3.50 |
| Electricity for cooling | 1001 kWh |
| Servicing | $120 a year |
| Total | $820 a year |
Ducted reverse cycle — $1,188 a year
One system, ducts to every room. The most comfortable and the most expensive to run, for two reasons that get conflated: the ducts lose heat, and it is conditioning the whole house.
| Conditions | The whole house |
| Heat it has to deliver | 5032 kWh a year |
| Coefficient of performance | 3.20 at 2.5 stars |
| Electricity for heating | 1573 kWh |
| Cooling it has to deliver | 4520 kWh a year |
| Energy efficiency ratio | 3.20 |
| Electricity for cooling | 1412 kWh |
| Servicing | $200 a year |
| Total | $1,188 a year |
How the calculation works
Space conditioning is harder to model than hot water, because the load depends on the building rather than on a fixed volume of water. The method here is deliberately simple enough to state in full.
Step one: how much heating and cooling the house needs
An average pre-2005 Melbourne house needs about 63 kWh of delivered heat per square metre per year and about 7.3 kWh of cooling. Those two numbers come from fitting Sustainability Victoria's published running costs, and everything else scales off them.
Step two: adjust for your climate
Scaled by heating and cooling degree days against a base of 18 °C, derived from the same Bureau of Meteorology monthly temperatures the hot water calculator uses for inlet temperature. Melbourne has 1,239 heating degree days and 173 cooling; Darwin has none and 3,508. Cooling is scaled by degree days to the power of 0.8 rather than linearly, because a tropical climate needs latent as well as sensible cooling and the raw ratio overstates it.
Step three: adjust for the building
A 5-star house needs 40% of the heating energy of a pre-2005 one and 75% of the cooling. A 6-star house, 30% and 60%. These are Sustainability Victoria's own multipliers. Insulation helps heating far more than cooling, which is why a single "efficiency" figure for both is always wrong about one of them.
Step four: adjust for what the system actually conditions
A ducted system delivers about 1.29 times as much conditioned energy as a multi-split in the same house, and a single split about half. That one factor covers both duct losses and the fact that a ducted system heats the whole house while a split heats a room.
Splitting those into separate multipliers double-counts. An earlier version of this calculator did exactly that and came out 25% under the benchmark on every multi-split row while matching ducted perfectly — which is how the error was found.
Step five: divide by the system's efficiency
Coefficient of performance for heating, energy efficiency ratio for cooling, both taken from the star rating on the label. A resistive electric heater is exactly 1.0 and cannot be otherwise.
Worked example
A 160 m² pre-2005 house in Melbourne with a 2.5-star multi-split:
Heat needed: 63.2 × 160 × 1.0 (pre-2005) × 1.0 (Melbourne) × 1.0 (multi-split)
= 10,112 kWh a year
At a coefficient of performance of 3.2: 10,112 ÷ 3.2 =
3,160 kWh of electricity
At 29.2c: $923 a year
Sustainability Victoria publishes $923 for that case. The methodology page lists the full comparison across sixteen of their figures.
Frequently asked questions
Why does the calculator ask for floor area rather than room size?
Because the systems being compared do different amounts of work, and floor area is the only common basis for that. Enter the whole house even if you are considering a single split — the results then show what a split costs to heat the part of it that it can reach, against what ducted costs to heat all of it. Entering a single room instead would make the split look like it conditions the whole property.
What if I do not know my home's star rating?
Use the build date, which is what the options are keyed to. Australia required 5-star from around 2006 and 6-star from 2012, and the 2023 code moved to 7. A house built before 2005 with insulation added later sits somewhere between the first two options — pick the pre-2005 one if the walls are uninsulated, which they usually are, since retrofitting wall insulation is rare and ceiling insulation alone gets you part of the way.
Why is my cooling cost so much lower than I expected?
Because in most of Australia cooling genuinely is cheap, and it runs for far fewer hours than people remember. A Melbourne house spends under $100 a year on refrigerated cooling and close to $900 on heating. The exceptions are Darwin and Brisbane, where the ratio inverts. If your summer bills are high, look at the pool pump and the second fridge before the air conditioner.
Does the calculator account for zoning?
Not explicitly, and that is a real limitation. A zoned ducted system used properly behaves more like a multi-split and less like the ducted figure shown here. If you have zoning and use it to heat two rooms rather than eight, your real cost sits between the two rows. Nothing on this site models how disciplined a household is about closing vents.
Are the installed costs reliable?
Less so than the running costs. They are surveyed ranges for a supply-and-install job in an accessible property, and ducted retrofits in particular vary enormously with roof space, existing ductwork and whether the switchboard needs upgrading. Treat the running costs as the solid figures and the installed costs as a starting point for quotes.