Kotatsu or
electric blanket:
which costs less?
But they warm different things. For sleeping or warming just yourself, choose the blanket; for sitting around a table with family, the kotatsu. Even if four people each use a blanket, it still costs less than one kotatsu.
On this page
What each one warms
Neither one heats the room's air. A kotatsu warms the space under its futon; an electric blanket warms the space between you and the blanket. The smaller the space, the less electricity it needs.
← Scroll sideways →
On the box, a kotatsu says about 500 W and a blanket about 50 W. Both cut power once warm, so compare the energy actually used per hour (Wh) instead (see the table below).
Cost comparison tool
One kotatsu costs the same no matter how many people sit at it. Electric blankets are one per person, so the cost multiplies.
Monthly electricity cost
Kotatsu: Yamazen furniture-style kotatsu (510 W), maker's figures (per hour: high ~170 Wh / low ~80 Wh; test conditions not confirmed). Electric blanket: Yamazen YFTKB-55 (55 W), maker's figures (high ~37 / medium ~25 / low ~10 Wh; average over 5 hours inside a cotton futon at a room temperature of 15°C). Unit price 31 yen/kWh (National Fair Trade Council of Household Electric Appliances guideline, revised July 2022).
But a kotatsu lets everyone eat and talk together while staying warm. The difference is a few hundred yen a month — choose by how you'll use it.
Cost per hour and per month
| Setting | Per hour | Per month 5 h/day, 30 days |
|---|---|---|
| Kotatsu, high (~170 Wh) | ~5.3 yen | ~791 yen |
| Kotatsu, low (~80 Wh) | ~2.5 yen | ~372 yen |
| Blanket, high (~37 Wh) | ~1.1 yen | ~172 yen |
| Blanket, medium (~25 Wh) | ~0.8 yen | ~116 yen |
| Blanket, low (~10 Wh) | ~0.3 yen | ~46 yen |
| For reference: kotatsu at its "510 W" label | ~15.8 yen | ~2,372 yen |
As the last row shows, calculating with the wattage on the box makes a kotatsu look about 3 times as expensive as it really is. Compare energy per hour (Wh).
To compare heaters that warm the whole room, see oil heater vs air conditioner.
Which one suits you?
Electric blanket if…
- Your bed feels cold when you get in
- You live alone and want the lowest bill
- You want something over your lap at the sofa or desk
- You don't have much storage space
Kotatsu if…
- You want to gather around one table with family or friends
- You spend a lot of time sitting on the floor
- Your feet get cold and you want to warm up sitting down
- You want to turn the air conditioner down and save overall
For how to choose, see our electric blanket guide and kotatsu guide.
Watch out for low-temperature burns
Even at a little above body temperature, warming the same spot for a long time can cause a low-temperature burn. Japan's NITE (National Institute of Technology and Evaluation) says it can happen in 3–4 hours at 44°C, 30 minutes to an hour at 46°C, and 2–3 minutes at 50°C. Some electric blankets reach about 51–52°C on the surface on high.
Instead: warm the bed before you get in, then switch to low or use the timer. NITE has received reports of low-temperature burns from electric blankets
Instead: when you get sleepy, switch it off and go to bed. Low-temperature burns from kotatsu have been reported too
Instead: they can touch the heater and scorch or smoke. Keep them away from the heater unit
Good to know if you live in Japan
-
Look for the PSE mark
Electric blankets and electric kotatsu are covered by Japan's Electrical Appliances and Materials Safety Act and must carry the PSE mark. Be careful with very cheap imports. -
Search in Japanese
Electric blanket is 電気毛布 (denki mōfu); 掛け敷き兼用 means it works both over and under you. Kotatsu is こたつ; the futon is こたつ布団, often sold separately. -
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.