Heaters | Updated Oct 2026
Warm from the feet up,
Warm from the feet up,
together.
A kotatsu is
just right.
The short version…
- Even on high, about ¥5.3 an hour (510W model)
- It heats only under the blanket — cheap, and great for cold feet and families
- It won't warm the room. Don't stuff blankets or floor chairs inside
Electricity cost calculator
For a kotatsu, calculate with energy used per hour, not the catalog wattage (like 500W). The figures below are maker-published values for the Yamazen furniture-style kotatsu (510W).
Per hour-
Per day-
Per month-
Same hours with other heaters? (per month)
At 31 yen/kWh (guideline unit price, revised July 2022). Kotatsu: Yamazen furniture-style kotatsu (510W), about 170Wh per hour on high / 80Wh on low. Compared with: electric blanket about 25Wh on medium (Yamazen YFTKB-55), oil heater about 470W (average once warm, 8 mats at 18°C; Kakaku.com estimate as of 2024), ceramic heater 1,200W on high (typical specs). Real costs vary with room temperature, futon thickness and model.
Professor Plug: on high, 5 hours a day for 30 days is about 790 yen a month — far less than a ceramic heater on high for the same time (about 5,580 yen).
Tip: put a floor mat or futon underneath. Blocking the cold from the floor lets you stay warm even on low.
Tip: put a floor mat or futon underneath. Blocking the cold from the floor lets you stay warm even on low.
Our picks by type
Choose a kotatsu by how many people will use it. A set with the futon avoids buying the wrong size.
A: Living alone, square (~75 cm)
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- Fits even a studio apartment
- A futon set avoids size mistakes
- About 5.0 yen/h (Yamazen casual kotatsu 300 W, high ~160Wh)
B: Family, rectangle (~105–120 cm)
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- Seats 2–4 people
- Inline switch, extension legs
- About 5.3 yen/h on high (Yamazen furniture-style kotatsu, 510W, about 170Wh)
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Who it suits — and who it doesn't
○ Good for you if…
- Your feet get cold and stay cold
- You want to gather around one warm table with family or friends
- You want to turn the air conditioner down and save money
- You often sit on the floor
× Not for you if…
- You want to heat the whole room
- Your room is too small to spread out the kotatsu futon
- You have nowhere to store the futon off-season
- You know you'd fall asleep in it
Just need to warm yourself? An electric blanket is even cheaper. For the whole room, an oil heater.
How it works, and how to use the futon
A heater unit under the tabletop warms the air and your feet inside the kotatsu futon (blanket). The futon traps the heat, which is why it stays warm on so little electricity.
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Three kinds of heater
| Type | Features | Good for |
|---|---|---|
| Quartz tube (石英管) | The classic. Affordable. Takes a little time to warm up | Keeping the price down |
| Halogen (ハロゲン) | Warm almost as soon as you switch on. Many use more power | Instant warmth when you get home |
| Flat (carbon etc., フラット) | Thin, so your legs don't bump it. Gentler warmth | Long, relaxed sessions |
General tendencies shared across explainers by furniture/appliance makers and power companies. To compare running costs, use each model's energy per hour (消費電力量).
5 tips for choosing
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Size the tabletop by people — and by futon
For one person, a small square (around 75 cm) is a common choice; for two or more, a rectangle (around 105–120 cm). The futon spreads well beyond the table, so plan for space at least a size bigger than the tabletop, and buy a futon made for that table size. -
Heater type
Halogen for instant warmth, flat for more leg room, quartz tube for a lower price (see the table above). -
Height: floor or chair?
Low type if you sit on the floor. For sofas and chairs, look at taller "dining kotatsu" (ダイニングこたつ) or models with extension legs (継脚). -
Inline switch and auto-off
A switch on the cord (中間スイッチ) lets you change the heat or turn it off without getting out. Motion sensors or auto-off help if you tend to forget. -
Will you use it in summer?
Without the futon it's just a table all year. Think about the tabletop design and where you'll store the futon off-season.
Common mistakes (and how to stay safe)
Based on accident cases and advice published by NITE (Japan's National Institute of Technology and Evaluation).
Mistake: pushing the futon, a floor chair or cushions inside the kotatsu
Instead: there have been cases where they touched the heater unit and scorched or caught fire. Keep them away from the heater
Instead: there have been cases where they touched the heater unit and scorched or caught fire. Keep them away from the heater
Mistake: drying laundry inside the kotatsu
Instead: clothes touching the heater have caught fire. Never put clothes inside
Instead: clothes touching the heater have caught fire. Never put clothes inside
Mistake: the power cord was trapped under a kotatsu leg or furniture
Instead: crushed cords have partly broken, short-circuited and caught fire. Don't trap, bend or twist the cord
Instead: crushed cords have partly broken, short-circuited and caught fire. Don't trap, bend or twist the cord
Mistake: falling asleep in the kotatsu
Instead: warming the same spot for a long time risks low-temperature burns. When you get sleepy, switch it off and go to bed
Instead: warming the same spot for a long time risks low-temperature burns. When you get sleepy, switch it off and go to bed
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
How can I cut a kotatsu's running cost?
Keep the heat in: put a mat or futon under the kotatsu futon (less heat lost to the floor), add a top cover, and switch to low once it's warm. On the Yamazen furniture-style kotatsu, high costs about 5.3 yen an hour and low about 2.5 yen — roughly half.
Can I sleep in the kotatsu?
Better not. Warming the same spot for a long time can cause a low-temperature burn. When you get sleepy, switch it off and go to bed. For a warm bed, use an electric blanket.
Is it cheaper than an electric blanket?
No — an electric blanket on medium is about 0.8 yen an hour vs about 5.3 yen for a kotatsu on high. A kotatsu for the family, a blanket for one. See kotatsu vs electric blanket.
Still not sure?
6 questions to find the heater that's just right for you.