Air Conditioning Running Costs Calculator Australia

Air conditioning is the single largest swing in a Melbourne power bill between March and December. Most people know that in general terms and have no idea what it means in dollars, because nothing on the unit or the remote tells them.

The number is not hard to work out. It needs one figure from the unit itself, one figure from your electricity bill, and an honest view of how many hours the system actually runs.

This page gives you a calculator that does the arithmetic, explains exactly what it is doing so you can check it, and then covers what actually drives the cost up or down. Nothing here is a marketing estimate. The figures come from your own equipment and your own tariff.

How the calculation works

There is no hidden model here. The whole thing is one line of arithmetic, and it is worth understanding so you can sanity check any figure a salesperson quotes you.

Electricity is billed by the kilowatt hour. A kilowatt hour is one kilowatt of draw for one hour. So the cost of running anything is its draw in kilowatts, multiplied by the hours it runs, multiplied by your rate.

1. Take the rated input power of the unit in kilowatts.
2. Multiply by the average load, as a fraction, to account for the system not always running flat out.
3. Multiply by the hours it runs.
4. Multiply by your electricity rate, converted from cents to dollars.

That gives cost per period. Nothing else is involved, which is why any running cost figure you are given should be reproducible from those four numbers.

Where to find your input power

This is the figure people get wrong, and getting it wrong throws the answer out by a factor of three or four.

Cooling capacity and power input are two different things. Capacity is how much heat the unit can move. Power input is how much electricity it draws to do that. A unit with a capacity of five kilowatts might draw only one and a half kilowatts, because it is moving heat rather than creating it.

• Look for a label on the side of the indoor unit or on the outdoor unit.
• The figure you want is described as power input, rated input or input power.
• It will be much smaller than the capacity figure.
• There are usually two, one for cooling and one for heating.

If the label has faded, the model number will find the specification sheet, and that always lists both figures.

Why the average load field matters

An older fixed speed air conditioner runs at full power or not at all. It draws its rated input, reaches the set temperature, switches off, and starts again when the room drifts. The average over an hour is well below the rated figure.

An inverter system behaves differently. It varies its output continuously, running hard to pull the room down and then settling at a much lower draw to hold it there. That is why inverters cost less to run despite having similar rated inputs.

Leaving the load at one hundred gives you the ceiling, which is the honest worst case. Dropping it to sixty or seventy shows what a system holding a steady room looks like, and the gap between the two numbers is the real value of a well sized system.

What your electricity rate should be

The default in the calculator is the flat usage rate under the Victorian Default Offer for one distribution zone, which is a published regulated figure rather than an estimate. Your own rate may be higher or lower.

• Victoria has five distribution zones and each has its own rates.
• Many households are on a time of use tariff rather than a flat rate, with a more expensive peak window in the late afternoon and evening.
• Market offers from retailers sit above and below the default offer.
• Your daily supply charge is separate and does not change with how much you run the air conditioner.

If you are on time of use, run the calculator twice, once at your peak rate and once off peak. The difference is usually the strongest argument for pre cooling the house before the peak window starts.

What actually drives your running cost

The calculator tells you what a system costs at a given set of numbers. Changing the numbers is where the savings are, and some levers are much larger than others.

Split, ducted and reverse cycle compared

The three system types cost different amounts to run, and the reason is straightforward. A bigger system moving more air through more space draws more power.

• A single split system conditioning one room has the smallest input power and the lowest running cost per hour.
• A multi head system draws more, because several indoor units share one larger outdoor unit.
• A ducted system has the largest input power of the three, and the highest hourly cost, because it is conditioning a whole house.

Cost per hour is the wrong comparison on its own though. A ducted system conditioning five rooms may well cost less than five split systems doing the same job, and a zoned ducted system running two zones costs far less than the same system running all of them.

Reverse cycle is not a fourth type. It means the system can heat as well as cool, and nearly every modern split and ducted unit does. Running it in heating is generally cheaper per unit of warmth than any electric resistive heater, because it moves heat rather than generating it.

If you are weighing the two main options against each other, our guide comparing a split system against a ducted system sets out the differences in more detail.

How much does it cost to run an air conditioner per hour?

It depends entirely on the input power of your unit and your electricity rate, which is why a single national figure is meaningless.

Work it out with the calculator above using your own nameplate figure. A small bedroom split system and a large ducted system can differ by a factor of five or more, so a figure quoted for someone else tells you very little about yours.

Is it cheaper to leave the air conditioner on all day?

Generally no, but the answer is less clear cut than it sounds.

A system pulling a hot house down from scratch works hard for a while, and there is a real cost to that. Holding a house at temperature all day costs less per hour but runs for far more hours, and in many homes the total is higher.

Where it does make sense is a well insulated home on a time of use tariff, pre cooled before the peak window and then held at a modest setting. Run the calculator both ways with your own hours and rates and the answer for your house will be obvious.

Does turning the temperature down make it cool faster?

No. Setting sixteen instead of twenty four does not make the system work harder in the early stage. It runs at full output either way until the room approaches the setting.

What it does do is run for longer and overshoot, because the system keeps going past the temperature you actually wanted. That is a straight waste of money and the common habit worth breaking.

Is ducted air conditioning expensive to run?

Per hour, yes, compared with a single split system, because it has a larger input power and conditions a much larger volume.

Per room, it is often competitive, and with zoning it can be cheaper than running several separate systems. The deciding factor is whether the zoning is used properly or whether the whole house runs every time somebody is warm in the lounge.

What it costs to run in heating

Most Melbourne systems are used in both seasons, and the running cost is not the same in each. The calculator works for heating too, you just need the heating input power rather than the cooling one.

Nameplates list both. The heating figure is usually slightly higher, because the system is working against a larger temperature difference on a cold morning than it is on a warm afternoon.

• Use the heating power input from the nameplate in place of the cooling figure.
• Set the days to cover a Melbourne winter rather than a summer.
• Expect the hours per day to be higher, since heating tends to run in the morning and again in the evening.

Two things worth knowing before comparing that number with any other form of heating. A reverse cycle system moves heat rather than producing it, so it delivers more warmth than the electricity it consumes. An electric resistive heater can never do better than the energy you put in.

Defrost cycles are the other difference. On a cold morning the outdoor coil ices up, and the system periodically reverses to clear it. That costs a little energy and briefly stops the warm air, which is normal rather than a fault.

Checking a quote against the calculator

The most useful thing this page can do for you is let you test a claim. If somebody quotes a running cost, ask which input power and which electricity rate they used.

1. Ask for the power input figure they applied and check it against the nameplate of the unit being quoted.
2. Ask which electricity rate they used and compare it with your bill.
3. Ask what load assumption sits behind it, since a figure calculated at half load is not comparable with one at full load.
4. Reproduce the figure here with those three numbers.

If the numbers do not reconcile, the quote is using assumptions that have not been stated. That is worth knowing before you compare it with anything else.

Using the number you now have

Once you know your cost per hour, the rest of the decisions get easier. You can see what an extra two hours a day actually costs across a summer, what a degree on the thermostat is worth, and whether an old system is expensive enough to justify replacing rather than repairing again.

The two figures worth writing down are your input power and your electricity rate, because those are the ones you will need every time.

If your system is drawing more than it should, running longer than it used to, or no longer holding the temperature it managed last summer, that is usually a maintenance problem rather than a tariff problem. We service split, multi head and ducted systems across Melbourne, and the price is confirmed with you before any work starts.