Oil heater or
air conditioner:
which costs less
to run?
People still choose oil heaters because they are silent, blow no air, and work in rooms without an air conditioner. You buy one for comfort, not to save money.
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Why the air conditioner wins: heat per kWh
An oil heater turns electricity into heat directly. 1 kWh of electricity gives about 1 kWh of heat.
An air conditioner doesn't make heat — it collects heat from the outdoor air and moves it inside (a heat pump). So it puts out more heat than the electricity it uses. Daikin's 6-tatami model (E series S225ATES), for example, gives 2.2 kW of heat from 470 W when it's 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×.
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Air conditioners lose efficiency as it gets colder outside, but they still give 2–3 times the heat of the electricity used even below freezing (Heat Pumping Technologies Magazine, April 2024). In very cold areas such as Hokkaido, choose a model made for cold climates.
Cost comparison tool
Oil heater costs come from a Kakaku.com estimate (De'Longhi model, as of 2024). Since nearly all of an oil heater's electricity becomes heat, we treat that as the heat needed to keep the room at that temperature, then calculate what an air conditioner would pay to deliver the same heat.
Monthly electricity cost
Oil heater: Kakaku.com estimate (De'Longhi; concrete apartment meeting the "new energy-saving standard", region IV; early-December Tokyo weather; 9 hours). 6 tatami 16°C ~10.1 yen / 8 tatami 18°C ~14.5 yen / 10 tatami 20°C ~20.9 yen per hour, average once warm. Air conditioner: the same heat delivered at the multiplier chosen above (cold day ~2.5× / 7°C ~4.7×). Defrost cycles and warm-up power are not included. Unit price 31 yen/kWh (National Fair Trade Council of Household Electric Appliances guideline, revised July 2022). 1 tatami ≈ 1.6 m².
The makers' official estimate (JIS conditions: Tokyo, wooden house, 20°C, 18 hours a day, November–April) puts a 6-tatami air conditioner at about 5.4 yen an hour. Different conditions, same conclusion: cheaper than an oil heater.
Why some articles say the oil heater is cheaper
You'll find articles online that reach the opposite conclusion. Most of them compare numbers measured under different conditions.
| Number you often see | Per hour | What it really means |
|---|---|---|
| AC (6 tatami) "470 W" | ~14.6 yen | Power while putting out a full 2.2 kW of heat (rated). Much less once the room is warm |
| AC "max 1,280 W" | ~39.7 yen | The ceiling when heating a cold room fast. It doesn't last |
| Oil heater "6 tatami 16°C average" | ~10.1 yen | Average once warm — about 0.33 kW of heat |
| Oil heater "high 1,200 W" | ~37.2 yen | Power at full output |
Put "AC rated (2.2 kW of heat)" next to "oil heater average (about 0.33 kW of heat)" and the air conditioner looks expensive — but it's putting out nearly 7 times the heat. Compare the same heat, and the air conditioner is cheaper.
Which one suits you?
Air conditioner if…
- You want the lowest electricity bill
- You want the room warm soon after you get home
- You're heating a larger room, like a living room
- Your room already has one (most Japanese rentals do)
Oil heater if…
- You want a silent, warm bedroom until morning
- Air blowing on your face or skin bothers you
- The room has no air conditioner and you can't install one
- It's a well-insulated room of about 6–8 tatami
About dryness: any heater lowers relative humidity as the room warms up. An oil heater blows no air, so you feel less of that dry air on your skin and throat. To keep humidity up, add a humidifier.
For how to choose an oil heater, see our oil heater guide.
Using them well
-
Check the AC's heating room size
"For 6 tatami" usually refers to cooling; heating covers a smaller room. Daikin's E series 2.2 kW model, for example, is rated for 5–6 tatami when heating (wooden house, south-facing). For a cold room, consider one size up. -
Oil heater in the bedroom, AC in the living room
Use the efficient air conditioner for the big room you spend the most time in, and the quiet oil heater for a small bedroom. You get both a lower bill and comfort. -
If you use both: warm up with the AC, keep warm with the oil heater
Oil heaters are slow to warm a room. Start with the air conditioner, then switch to the oil heater for quiet warmth. On cost alone, though, keeping the AC on is cheaper. -
Keep the set temperature modest
Lowering the AC's heating from 21°C to 20°C saves about 1,650 yen a year, according to Japan's Agency for Natural Resources and Energy. The same goes for oil heaters: a higher setting costs more.
Good to know if you live in Japan
-
Ask before installing an air conditioner in a rental
Installing one usually means drilling a hole for the pipes, so check with your landlord or management company first. If you can't, an oil heater needs only an outlet. -
Room sizes are in tatami
Product listings say things like "6畳" (6 tatami ≈ 10 m²). Look for 暖房 (heating) next to the size — that's the heating rating. -
Your real price per kWh depends on your contract
We use 31 yen/kWh. Check your bill or your power company's app for your own rate.
Still not sure?
Answer 6 questions and find the heater that's just right for you.