Air Conditioner Running Costs in Japan: Cost per Hour, and Leaving It On vs Switching It Off

Typical air conditioner running costs

These are the costs at 31 yen/kWh, used 8 hours a day for 30 days. Power consumption uses a value close to the average while running, not the rated figure.

By season, cooling a 6–8 tatami room for the 3 months from July to September costs 8,928 yen, and a 14-tatami living room costs 17,856 yen. Heating for the 5 months from November to March costs 18,600 yen for 6–8 tatami and 37,200 yen for 14 tatami. In the same room, a winter of heating works out to roughly twice a summer of cooling.

Why heating costs more

Heating uses more electricity than cooling because the gap between outdoor and indoor temperature is larger. In summer, cooling from 35°C outdoors to 27°C indoors is a difference of 8°C. In winter, heating from 3°C outdoors to 20°C indoors is a difference of 17°C. The amount of heat the unit has to move translates directly into power use.

• Larger temperature gap: in winter, more heat has to be moved to stay comfortable.
• Defrost cycles: in cold weather, frost forms on the outdoor unit. Heating stops while it melts, and restarting uses more power.
• Longer hours: some summer days need only nighttime use, but winter often means both morning and evening.

The difference also shows up in your bills. Meters bill for the previous month, so electricity used in midwinter appears on February and March bills, and midsummer use on the September bill. If an average month is 1.00, the February bill is about 1.32 times and June about 0.76 times, with the winter peak higher than summer.

Which is cheaper: leaving it on or switching it off often?

Here's a comparison of cooling a 6–8 tatami room (400W average) for 24 hours straight and only for the 12 hours you're home.

If you'll be out for a long time, switching it off is definitely cheaper. Comparing by average power, half the running time means roughly half the cost.

But short trips are different. Once the unit has settled at the set temperature, leaving it on for 30 minutes costs only about 2.3 yen (150W × 0.5 hours). Switch it off, though, and the 30-minute restart when you get back runs at around 1,000W, which alone costs about 15.5 yen. For a trip of 30 minutes to an hour, switching off saves a few yen, and the startup peak can be greater than that.

How to lower your air conditioner's cost

An air conditioner uses a lot at startup, then holds its state with little power. Saving comes down to two things: keeping it in that stable state for longer, and reducing the power it uses there.

• Use auto mode: starting on low takes longer to reach the set temperature and can end up using more power. Starting strong and then automatically throttling down is more efficient.
• Clean the filter: dust clogging reduces airflow and takes extra power to hold the same temperature. Aim for once every 2 weeks.
• Add a circulator fan: 30W costs 0.93 yen per hour. Warm air collects at the ceiling and cold air at the floor, so mixing it lets you moderate the set temperature while staying just as comfortable.
• Keep the area around the outdoor unit clear: anything in front of the outlet traps heat and lowers efficiency. In summer, a shade against direct sunlight also helps.
• Block window heat with curtains: windows account for much of a room's heat gain and loss. Thick curtains or insulating film reduce the heating and cooling load itself.

If you've kept an old air conditioner running, replacing it can lower power use significantly. If you know the power of your current model and a new one, the "Compare electricity costs" tab in the Electricity Cost Calculator shows how many years it takes to recover the cost of replacing it.

Calculate for your own air conditioner

1. 1

   Choose the air conditioner from the appliance list

   In the "Calculate by appliance" tab, choose cooling or heating and the room size (6–8 or 14 tatami) to fill in the average power and a guide of 8 hours a day.

2. 2

   Change the hours to fit your use

   Shorten the daily hours if you use it only at night, or lengthen them if you work from home and use it during the day. Costs per hour, day, month and year appear together.

3. 3

   See the difference from leaving it on

   Choose "Air conditioner left on / switched off often" in the "Compare electricity costs" tab to see the difference between 24 and 12 hours per day, month, year and 10 years. You can edit the hours and wattage.

To compare with other heaters, see comparing heater electricity costs. The calculation itself is explained in how to calculate electricity costs.

FAQ

How much does an air conditioner cost per hour?

At 31 yen/kWh, a 6–8 tatami unit costs about 12.4 yen for cooling and 15.5 yen for heating, and a 14-tatami living room about 24.8 yen for cooling and 31 yen for heating. These are averages while running. In the first 30 minutes to an hour after you turn it on, power reaches around 1,000W, which comes to about 30 yen per hour.

Is it cheaper to leave an air conditioner on 24 hours?

For long absences, switching it off is cheaper. Cooling a 6–8 tatami room for 24 hours costs 8,928 yen a month and 12 hours costs 4,464 yen, a difference of 4,464 yen a month. For a trip of 30 minutes to an hour, though, leaving it on can be cheaper, because switching off and restarting uses around 1,000W at startup.

Which costs more, heating or cooling?

Heating. The gap between outdoor and indoor temperature is larger in winter, so even for 6–8 tatami, heating averages around 500W against 400W for cooling. Heating also runs for longer, so a summer of cooling (3 months) costs about 8,900 yen while a winter of heating (5 months) costs about 18,600 yen, roughly twice as much.

How much does an air conditioner cost per month?

Used 8 hours a day for 30 days, a 6–8 tatami unit costs 2,976 yen for cooling and 3,720 yen for heating, and a 14-tatami unit 5,952 yen for cooling and 7,440 yen for heating (at 31 yen/kWh). To estimate your actual bill, use the effective rate of around 40 yen, which includes the base charge and renewable energy surcharge, and it comes to about 1.3 times these figures.

How can I lower the cost of air conditioning?

The basics are these five: use auto mode, clean the filter once every 2 weeks, mix the air with a circulator fan, keep the front of the outdoor unit clear, and reduce heat transfer through windows with curtains. Repeatedly switching off and on for short trips can actually cost more because of the power used at startup.