Want to heat the whole room
for the least money?
Then the air conditioner
is just right.
The short version…
- A 6-tatami room costs about 2–4 yen an hour — the cheapest way to heat a whole room
- Out for 30 minutes? Leave it on. Out for 2 hours? Turn it off (Daikin's test)
- Set it 1°C lower and clean the filter: about 2,600 yen saved a year
Cost calculator
We take the heat a room needs and divide by how efficiently the air conditioner makes that heat. Efficiency drops on cold days, so pick the weather too.
The same heat from other heaters (per month)
Heat the room needs: Kakaku.com's estimate for a De'Longhi oil heater once the room is warm (2024; concrete apartment, early-December Tokyo weather, 9 hours): 6 tatami/16°C about 0.33 kWh, 8 tatami/18°C about 0.47 kWh, 10 tatami/20°C about 0.67 kWh per hour. The air conditioner is assumed to make that heat at about 2.5× (cold day) or about 4.7× (7°C outside; Daikin S225ATES: 2.2 kW of heat from 470 W). Start-up and defrost power are not included. Higher in poorly insulated homes and colder regions. 31 yen/kWh (guideline price of Japan's Home Electric Appliances Fair Trade Conference, revised July 2022). 1 tatami mat is about 1.6 m², so 6 tatami is about 10 m².
Going out: turn it off or leave it on?
Daikin tested this one winter in two apartment rooms in Kyoto. Pick how long you'll be out.
| Test | Left on | Turned off |
|---|---|---|
| Off/on every 30 min daytime, 6:00–18:00 | 7.8 kWh ~242 yen | 11.2 kWh ~347 yen |
| Off/on every 30 min night, 23:00–6:00 | 5.0 kWh ~155 yen | 8.5 kWh ~264 yen |
| Out for 2 hours evening, 18:00–23:00 | 3.4 kWh ~105 yen | 2.4 kWh ~74 yen |
| Whole day (24 h) off while asleep and out | 12.7 kWh ~394 yen | 11.6 kWh ~360 yen |
Daikin Industries news release (February 16, 2018). December 25–26, 2017, a 15-year-old apartment building in Kyoto, heating at 24°C with auto fan; high of 7.8°C on the 26th. We recalculated the yen at this page's 31 yen/kWh (Daikin used 27 yen/kWh). Results vary with the home and the weather.
How much can you save?
Tick what you'll try and we'll add up the yearly savings. Figures are estimates from Japan's Agency for Natural Resources and Energy.
Agency for Natural Resources and Energy, "Energy saving without strain" (2.2 kW air conditioner, 6°C outside, heating 9 hours a day, etc.), converted at 31 yen/kWh.
Our picks by type
- 2.2 kW heating from 470 W (Daikin E series)
- Heats down to −15°C outside
- 6 tatami at 16°C: about 2–4 yen an hour
- The same E series, mainly for 10 tatami
- For a living room
- 10 tatami at 20°C: about 4–8 yen an hour
Products and prices load from Rakuten Ichiba when you open the page. Air conditioners need professional installation — check whether the listing says 標準工事費込み (standard installation included).
Want the details? (tap to open)
Who it suits — and who it doesn't
○ Good fit
- You want the living room or your room warm for hours
- You want the lowest possible bill
- You'd rather not buy kerosene or worry about flames
- Your room already has an air conditioner
× Not a good fit
- You need heat where there's no air conditioner — changing room, toilet
- You dislike warm air blowing on you, or your throat dries easily
- You rent and can't install a new unit
- You only need to warm your feet or yourself
How it works: why it's so cheap
An air conditioner doesn't "make" heat from electricity. It collects heat from the outside air and carries it indoors (a heat pump). Even cold winter air holds heat; the outdoor unit gathers it and the indoor unit blows it out as warm air.
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Daikin's 6-tatami model (E series S225ATES) gives 2.2 kW of heat from 470 W at 7°C outside (about 4.7×). The Japan Refrigeration and Air Conditioning Industry Association puts the average for energy-saving models at about 5.5×. The colder it is outside, the less heat there is to collect, but even below freezing they're said to manage 2–3×.
On cold, damp days frost forms on the outdoor unit, and heating pauses for a while to melt it (defrost mode). That's normal, not a fault.
5 tips for choosing
-
"For 6 tatami" means cooling. Check the heating size
The big "おもに6畳用" (mainly for 6 tatami) on the box is for cooling. Heating covers less: the Daikin S225ATES lists 5–6 tatami (暖房の畳数). The smaller number is for a wooden house, the larger for a concrete apartment. -
In cold areas, check "low-temperature heating capacity"
低温暖房能力 shows how much heat it gives when it's very cold outside (2°C in the Japanese standard test). The S225ATES is rated 2.2 kW but gives 2.8 kW at low temperature. A bigger number means it holds up better on cold mornings. -
Snowy or sub-zero regions: consider a cold-climate model
Even Daikin's standard E series heats down to −15°C outside. For colder or snowier areas, compare each maker's cold-climate (寒冷地) models. -
Automatic filter cleaning saves effort
A clogged filter raises your bill. Without self-cleaning, Daikin recommends cleaning the filter every two weeks. -
Check the outlet and installation cost
The S225ATES runs on a standard 100V 15A outlet, but bigger models (around 14 tatami and up) are often 200V and may need a new outlet. When buying online, check whether installation (標準工事費込み) is included.
Common mistakes
Instead: Warm air rises, so point the louvers down. "Auto" fan speed warms the room faster and wastes less (Daikin's advice)
Instead: Keep the outdoor unit's vents clear. In snowy areas, clear the snow around it
Instead: 1°C lower saves about 1,650 yen a year. Make up the difference with a wearable blanket or lap blanket, and add window insulation film or curtains
Instead: An air conditioner warms the air but adds no moisture, so humidity drops. Use a humidifier and aim for 50–60%
Good to know if you live in Japan
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Remote control words
暖房 (danbō) = heating, 冷房 (reibō) = cooling, 除湿 (joshitsu) = dry, 運転／停止 = on/off, 風量 = fan speed, 風向 = airflow direction, 自動 = auto. A camera-translation app works well for the buttons. -
Renting? Ask first
Many rentals already have an air conditioner. If yours doesn't, ask your landlord or management company before buying — installation means drilling a hole in the wall for the pipes. -
Check the outlet near the unit
Japanese outlets for air conditioners come in different shapes for 100V and 200V. Look at the outlet high on the wall and compare it with the product's plug shape (プラグ形状). -
Your price per kWh may differ
We calculate with 31 yen/kWh, the guideline price used in Japanese catalogs. Your actual price depends on your power company and plan — check your monthly bill (検針票 / your company's app).
FAQ
How much for a whole winter left on?
It's blowing cold air or stopping. Is it broken?
Can I leave it on while I sleep?
Is it really cheaper than an oil or ceramic heater?
Still not sure?
Answer 6 questions to find the heater that's just right for you.