Heaters | Updated Oct 2026
No dry air, no noise.
No dry air, no noise.
Warm the whole room, gently.
An oil heater is
just right.
The short version…
- About ¥14.5 an hour for an 8-mat room at 18°C — it throttles down once warm
- No air blowing, and quiet. Great for bedrooms and kids' rooms
- Slow to warm up — set the timer to switch it on early
Electricity cost calculator
The average cost once the room is warm comes from Kakaku.com's estimate for a De'Longhi oil heater (as of 2024).
Per hour-
Per day-
Per month-
What if you used the catalog numbers? (per month)
Average cost: Kakaku.com estimate (De'Longhi model, concrete apartment meeting Japan's "new energy-saving standard" (region IV), early-December Tokyo weather, 9 hours, 31 yen/kWh). 6 mats/16°C about 10.1 yen/h, 8 mats/18°C about 14.5 yen/h, 10 mats/20°C about 20.9 yen/h (with eco mode: about 8.9 / 12.1 / 16.1 yen/h). Higher in poorly insulated homes, colder regions or at higher settings. "High" and "medium" bars assume a 1,200W high / 700W medium model. 1 tatami mat is about 1.6 m².
Professor Plug: 8 mats at 18°C, 8 hours a day for 30 days is about 3,500 yen a month on a standard model, or about 2,900 yen with eco mode.
That's less than half of the ~8,900 yen you'd get from "1,200W × 8 hours". But a higher setting or a colder room closes that gap fast.
That's less than half of the ~8,900 yen you'd get from "1,200W × 8 hours". But a higher setting or a colder room closes that gap fast.
Our picks by type
Choose an oil heater by room size and whether it has eco mode.
A: Bedroom / kids' room (up to ~8 mats)
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- Max ~1,200W, 24-hour timer
- Child lock, tip-over shut-off
- About 10 yen/h for 6 mats at 16°C (estimate)
B: Eco mode, larger rooms (8–10 mats)
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- Digital controls, eco mode
- Casters for easy moving
- About 12 yen/h for 8 mats at 18°C (estimate)
* Products and prices are loaded from Rakuten Ichiba when the page opens.
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Who it suits — and who it doesn't
○ Good for you if…
- Air-conditioner heat dries your throat or skin
- You want a quietly warm bedroom until morning
- You have small kids or pets and worry about flames or hot air
- You live in a well-insulated place, like a concrete apartment
× Not for you if…
- You want the room warm the moment you get home
- You want to heat a large, drafty wooden room with just this
- You want to carry it from room to room often
- The absolute lowest bill is your top priority
Need heat fast? A ceramic heater may fit better. Only need to warm yourself? Try an electric blanket.
How it works — and why the bill is lower than you'd think
Electricity heats oil sealed inside, and the heat radiates from the fins. Warm air circulates slowly and the walls and floor warm up too, so the whole room gets warm without any fan. The oil isn't fuel — you never refill it.
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That's why calculating with the catalog's "1,200W" overestimates the bill. Real cost depends heavily on room size, temperature setting and insulation.
Great rooms, poor rooms
◎Bedroom
◎Kids' room
○Home office
○Apartment room
△Large living room
△Cold wooden room
×Changing room / toilet
×Bathroom / outdoors
* It's poor for places you only use briefly and want warm instantly. Don't use it near water or in humid places (maker's warnings).
5 tips for choosing
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Pick a room-size rating a bit bigger than your room
Boxes list a room size such as "8–10 mats" (適用畳数). For poorly insulated rooms or cold regions, go by the smaller number.Your room What to look for 6-mat bedroom Rated up to ~8 mats, max ~1,200W 8-mat room Rated 8–10 mats, max ~1,200W 10 mats or more Rated 10+ mats, max ~1,500W. Consider using it with the air conditioner -
Eco mode / automatic temperature control
Some digital models have an eco mode that runs slightly below your set temperature. In the estimate above, eco mode saves about 1–5 yen per hour. -
24-hour timer: on before you wake, off after you sleep
It's slow to warm up, so a timer that switches it on before you wake or get home helps a lot. It stays warm for a while after switching off, so set "off" a little early. -
Weight and casters
Oil makes it heavy — the De'Longhi RHJ21F0812 is about 13 kg (maker's figure). If you'll move it between rooms, choose one with casters. -
Safety features and surface heat
Look for tip-over shut-off, child lock and overheat protection. There's no flame, but the surface gets quite hot (some models advertise about 80°C), so consider a cover or guard if kids or pets can reach it.
Common mistakes
Mistake: switched it on after getting home — it took ages to warm up
Instead: use the timer to start it before you wake or get home. For fast warmth, run the air conditioner too, then switch to the oil heater alone
Instead: use the timer to start it before you wake or get home. For fast warmth, run the air conditioner too, then switch to the oil heater alone
Mistake: left it on high in a cold room and the bill climbed
Instead: don't set the temperature too high. Add window insulation film or thicker curtains to keep the heat in
Instead: don't set the temperature too high. Add window insulation film or thicker curtains to keep the heat in
Mistake: placed it near laundry or curtains, or under a desk
Instead: keep it at least 20 cm from walls and curtains and at least 1 m from people and furniture. Nothing on top, never under a desk (De'Longhi FAQ)
Instead: keep it at least 20 cm from walls and curtains and at least 1 m from people and furniture. Nothing on top, never under a desk (De'Longhi FAQ)
Mistake: ran it with a hair dryer or microwave and the breaker tripped
Instead: it draws 1,200–1,500W while warming up, so don't overlap it with other big appliances
Instead: it draws 1,200–1,500W while warming up, so don't overlap it with other big appliances
Good to know if you live in Japan
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Buy a heater made for Japan (100V)
Japan's household power is 100V. A heater built for 220–240V countries won't work properly here, and adapters don't fix that. Choose a model sold in Japan. -
Look for the PSE mark
Electric heaters, electric blankets and kotatsu are covered by Japan's Electrical Appliances and Materials Safety Act. Products sold in Japan must carry the PSE mark — be careful with very cheap imports from marketplaces. -
Manuals are usually in Japanese
Many makers post their manuals as PDFs on their websites. A camera-translation app works well for the safety page and the control panel. -
Shopping in English
Amazon.co.jp can be switched to English in the language settings. Product titles are often still in Japanese — search with the Japanese name (shown on this page) to find more options. -
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
Is it true oil heaters are expensive to run?
To keep a room at the same temperature, it costs more than an air conditioner (6 tatami at 16°C: about 10.1 yen an hour vs about 2–4 yen). But it's far less than "1,200 W × hours" suggests. See oil heater vs air conditioner.
Can I use an extension cord or power strip?
No. De'Longhi's FAQ (updated April 8, 2025) says to plug it directly into a wall outlet (15 A), not shared with other appliances. Extension cords and power strips can overheat and start a fire. Clean dust off the plug and outlet regularly, too.
Does the oil need topping up? How do I throw it away?
The oil is sealed, so it never needs refilling or changing. To dispose of one, check your local rules first — some municipalities take it as oversized garbage, some don't. De'Longhi is reported to run a take-back recycling service for its own heaters (you pay shipping). Don't drill or take it apart to drain the oil yourself.
Still not sure?
6 questions to find the heater that's just right for you.