Work out yours in five steps
Find the input power
Look in the manual or the specifications for the input power in kW, for cooling and for heating. Mitsubishi Electric says capacity is what the unit delivers and input power is what it draws from the supply, so the size on the box won't do.
Estimate the hours
How many hours a day it runs, and how many days a season. A hot week in January isn't the same as a mild March, so think in seasons, not single days.
Turn it into kWh
Input power in kW times hours gives kilowatt hours (kWh), the unit your bill uses. As an example with made-up round numbers, a unit drawing 2 kW for 5 hours uses 10 kWh at most.
Apply your rate
RAA's method multiplies the power by the rate you pay in cents per kWh. Your rate is on your bill. If the bill shows more than one rate, use the one for the hours you'd run the unit.
Or let the tool do the sums
Our running cost tool does the multiplying with your unit's figures and your own rate.
Why your real number can be lower
That sum is a ceiling, not a forecast. RAA says its figures assume the maximum draw, and that a unit switching off and on to hold a temperature uses less power on average.
Inverters widen the gap. CHOICE says modern splits are inverter models that adjust their output as needed, so actual running costs may be lower than the rated figures. The Energy Rating calculator makes the same point: units may operate below their rated capacity.
The house matters as much as the unit. CHOICE says that in a well-insulated, well-sealed house, a split can keep a comfortable temperature while running at very low power.
Use the energy label for a yearly figure
The zoned energy rating label shows how much energy a unit uses per year for cooling and for heating, Mitsubishi Electric says, and the lower that figure, the less it is to run. It's the quickest way to compare two models.
Compare units of a similar size, rated for your climate zone, as the ACT guide suggests. The Australian Government's Energy Rating calculator lets you enter the tariff from your bill for a closer estimate, and fills in your climate from your postcode. Our page on energy ratings explains the label.
Heating with reverse cycle goes further than you'd think
When it's heating, a reverse cycle unit delivers more than it draws. The ACT Government says it turns every unit of electricity into 3 to 6 units of heat, where a portable electric heater makes just one.
That's why the input power, the number you multiply, is a fraction of the heat it puts out. If you're comparing it with a fan heater or an oil column heater, compare what each one draws, not what each one is rated to deliver.
What pushes your number up or down
The thermostat. The Energy Rating calculator suggests 18 to 20 degrees in winter and 25 to 27 in summer, and says each degree further could add 10% to your electricity bill. Solar Victoria gives the same ranges, while the ACT Government suggests cooling at 23 degrees or above, so sources differ a little.
The filters. Daikin says replacing a blocked filter with a clean one can lower energy use by anywhere from 5% to 15%. Its general rule is to clean them every two weeks, but go by your own manual.
The rooms you run. Solar Victoria says to heat or cool only the areas you're using, by zoning a ducted system or closing doors. On ducted, the ACT guide says at least R1.5 insulation on the ducts cuts heat loss and lowers running costs.
The age of the unit. Solar Victoria's 2021 buyers guide says a system more than 15 years old will typically use more than three times the energy of a modern reverse cycle air conditioner.
Night and away settings. Mitsubishi Electric's i-save mode is one example: it sets the temperature 2 to 3 degrees warmer when cooling, or cooler when heating, for empty rooms and sleep.
What to have in front of you
- The model number, so you can find the specifications.
- The input power for cooling and for heating, in kW.
- Your electricity bill, with the rate per kWh.
- A rough idea of hours per day and days per season.
- The yearly energy figure from the label, if you're comparing new units.
What you can do, and what needs a technician
You can
- Work out your use with the method above or the running cost tool.
- Clean the filters the way your manual says.
- Keep the thermostat in the suggested ranges and close the doors to unused rooms.
- Keep leaves and clutter away from the outdoor unit. Daikin says debris makes it run less efficiently.
Leave to a licensed installer
- A service covering the coils, the refrigerant charge, the electrical connections and the drains, as Daikin describes.
- Finding out why a unit runs constantly or struggles to reach temperature.
- Advising whether an old unit is worth keeping or replacing.
- Insulating or sealing ducts on a ducted system.
What we'd do
What we'd do
We'd do the sum once properly, with the input power from the manual and the rate from our own bill, so we know the ceiling. Then we'd chase the easy wins: the thermostat in the suggested range, clean filters, doors shut. If the unit's more than 15 years old, we'd ask a specialist to quote on a replacement, because the energy gap Solar Victoria describes is a big one.
