Hot-water bottle or electric foot warmer:
which costs less?
But both are a few yen a night at most — a few hundred yen over a winter. What matters more is how you use them. Japan's Consumer Affairs Agency says to take the hot-water bottle out once the bed is warm, and Tokyo says the same for electric foot warmers. Think of both as tools for warming the bed before you get in.
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Cost per night and surface temperature
| Item | 30 min before bed | All night (8 h) | Surface temperature |
|---|---|---|---|
| Hot-water bottle 2 L at 80°C | Heating the water ~¥4.7 (however long you use it) | Depends on the water | |
| Electric foot warmer (flat) Koden VWH601H (60 W) | High ~¥0.1 | Low ~¥0.1 / high ~¥1.4 | High ~60°C / med ~45°C / low ~30°C |
| Electric foot warmer (dome) Koden VWY601H (60 W) | High ~¥0.1 | Low ~¥0.2 / high ~¥2.1 | High ~60°C / med ~45°C / low ~30°C |
| Electric blanket Koden CWB551 series (55 W) | High ~¥0.5 | Medium ~¥4.5 | High ~52°C / med ~36°C |
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Foot warmers and electric blanket: from the maker's published energy per hour (flat: high 5.5 / medium 3.2 / low 0.5 Wh; dome: high 8.6 / medium 4.1 / low 0.9 Wh; blanket: high 31 / medium 18 Wh). Hot-water bottle: the heat to take 2 L of water from 15°C to 80°C (about 0.15 kWh) boiled with electricity, excluding kettle heat loss (real cost is a little higher).
Winter cost by how you use it
Pick an item and how you use it.
Winter is December to March, about 120 days. Hot-water bottle: boiled with electricity, excluding heat loss. Foot warmer: Koden VWH601H; electric blanket: Koden CWB551 series, published figures.
Low-temperature burns: temperature × time
A low-temperature burn can happen at a pleasantly warm temperature if the same patch of skin stays in contact for long. The Consumer Affairs Agency gives these guides: 3–4 hours at 44°C, 30 minutes to 1 hour at 46°C, 2–3 minutes at 50°C.
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The Consumer Affairs Agency received 363 reports of hot-water bottle accidents from September 2009 to October 2017, 240 of them burns. Of 108 reports from November 2015 to October 2020, 31 were serious burns taking more than a month to heal. Some people were burned even with a cover on.
Instead: take it out or switch it off once the bed is warm (Consumer Affairs Agency, Tokyo). For warmth all night, use an electric blanket on a low setting
Cautions by type of hot-water bottle
| Type | Cautions |
|---|---|
| Fill with hot water | Don't use with too little water (metal or hard plastic). For types you can heat on a flame or IH hob, always remove the cap first |
| Microwave | Follow the stated power and time. Don't use auto or "leave it to me" modes |
| Rechargeable (electric heat storage) | Don't charge it under bedding or a cover. Don't use it while charging |
Source: Consumer Affairs Agency. Whatever the type, check for cracks or tears before use, and check whether it's subject to a recall.
Which one?
Good to know if you live in Japan
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Search in Japanese
Hot-water bottle is 湯たんぽ (yutanpo). Electric foot warmer is 電気あんか (denki anka). Rechargeable types are 充電式湯たんぽ or 蓄熱式湯たんぽ; microwave types are レンジ湯たんぽ. -
Look for the PSE mark on electric foot warmers
Household power here is 100V. Electric foot warmers (電気あんか) are covered by Japan's electrical safety law, so buy one made for Japan with the PSE mark. For rechargeable hot-water bottles, follow the maker's charging instructions. -
Your electricity rate may differ
We use ¥31/kWh, the industry guideline. Your actual rate depends on your plan and power company.
FAQ
Is it cheaper to boil the water with gas?
Can I keep a hot-water bottle in bed all night if I wrap it in a towel?
What about older family members?
Which heater is right for you?
Answer 6 questions and find the heater that's just right for you.