Buying a kotatsu for a 90-day Tokyo winter stay

The kotatsu sits in every Tokyo winter listicle. The low table, the quilt, the heater under the frame. The picture is always the same: a cup of tea, an orange on the tabletop, a cat. The piece writes itself.

I bought one in late November my first winter and sold it in late February on Mercari. That was a 92-day stay. The math worked out, but not the way I'd expected.

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What the kotatsu does, and what it doesn't

A こたつ (kotatsu — low table with a heating element bolted under the frame, a quilt clamped between top and frame) heats the air your legs sit in. Not the room. The thermometer on the wall stays at 13°C all evening. Your feet are 30°C under the quilt. The rest of you is jacket-and-scarf, indoors, drinking tea.

I forget how distinct that feels until I describe it. You don't warm up. You go horizontal. You put your legs in. The body below the waist enters one climate. The body above stays in the cold one. You stop wanting to leave. The verb usually paired with kotatsu is 入る (hairu — to enter), not 座る (suwaru — to sit). You enter it the way you enter a bath.

What the listicle picture does not show is what happens when you stand up to make more tea. The room is 13°C. You take three steps. Your legs forget the heater immediately. By the time you're back, you are colder than when you left.

This is the kotatsu's actual register. It is exquisite for one task. It does that task badly when you have to keep moving.

The four winter tasks, and what wins each

A 90-day stay in Tokyo, December through February, has four heating tasks I can name:

The desk hours. You work nine to six, mostly at the table you also eat at. The aircon runs overhead. It works. Your hands are warm because you are typing.

The shower minutes. Tokyo bathrooms are not heated. The wall tiles are 11°C in late January. You undress in a 12°C room. You step into a 9°C stall. The thirty seconds before the water warms are the worst thirty seconds of the day.

The evening, sitting still. Six pm to ten pm. You are reading, watching something, eating dinner that's already cooled, scrolling. You are not moving from the seat. This is the kotatsu's hour.

The night. You sleep under the futon. The room drops to 9°C by 4am if you turned the aircon off. You should turn it off. Running it overnight at 22°C in a 6畳 (rokujō — six-tatami room, around 10m²) is ¥150 to ¥250 of electricity. The air also dries to nosebleed humidity by week two.

A 1,200W ceramic heater from Yamada Denki for ¥3,800 beats the kotatsu at three of these. The small one is twenty centimeters tall and fits in a backpack. You stand it in the bathroom doorway five minutes before you shower. The room is 18°C when you walk in. You aim it at your shins under the desk on the days the aircon is fighting a draft. You aim it at your face for the first ninety seconds you sit on the futon at night, while you read one page and turn the lamp off.

The kotatsu does the evening. Nothing else really competes with it for the evening. But the evening is one task of four.

What the math actually looks like

I bought my first kotatsu used on Mercari for ¥4,200. Pickup was at a Yamanote station, from a graduate student moving back to Osaka. A new set at Nitori on Meguro-dōri runs ¥9,800 to ¥24,800 (table, quilt, heater, optional rug). The basic glass-top model runs ¥12,800.

The element draws 200 to 600 watts depending on the dial setting. Six hours an evening on medium (about 400W) at ¥31 per kWh is ¥74 a day. Across 90 days, that is roughly ¥6,700 of electricity. You won't use it every evening. Realistically ¥4,000 to ¥5,000.

The ceramic heater is a different shape. 1,200W on high, but used in five-to-fifteen-minute bursts. Bathroom warm-up before the shower. Futon warm-up before bed. Desk-shin blast for the worst hour of the afternoon. Maybe forty minutes a day of active use. That is 800Wh, or ¥25 a day. Across 90 days, ¥2,250.

Then there's the appliance itself, divided across the days you used it. A new ¥12,800 kotatsu set used for 90 days and resold on Mercari for ¥6,000 is ¥6,800 of net cost. That is ¥75 a day. The ¥3,800 ceramic heater resells for ¥1,500, or goes in the 粗大ごみ (sodai gomi — bulky waste) ticket bin for ¥400. Net ¥2,300 to ¥3,400, or ¥26 to ¥38 a day.

Stack them: kotatsu at maybe ¥120 a day all-in, heater at ¥50 to ¥65. The heater is half the cost across a 90-day stay, and it wins three of the four tasks.

So why does anyone buy the kotatsu?

The argument for buying it anyway

The argument is not the math. The argument is the evening, sitting still. That hour is one the rest of the apartment gives you nothing for. The aircon dries the air. The space heater hums. The futon does not function as a couch. It is also the bed. You are not going to lie on the bed at 7pm with the lamp on. The kotatsu is the only piece of furniture that works as a place to spend an evening on purpose.

The first January I had one I read seven novels. I was in Setagaya, fourth floor, a 22m² 1K, one window facing east. The aircon was the only heat. I'd come home at six and plug the kotatsu in by 6:15. I would not stand up for three hours unless the kettle was empty. The room was 13°C the whole time. My back ached from the floor angle. My ankles were 30°C. I never wanted to leave.

The next year I tried to do it with just the heater. Read maybe two novels in the same window of evenings. The heater is utilitarian. You don't sit at it. You aim it at something and walk away.

This is not math. This is what the apartment is for.

The Mercari resale, in practice

If you buy used and sell used, the kotatsu math gets better. The pickup model is the friction. You message the buyer. They propose a station. You carry the table and the quilt to the station in a packing-tape-and-cardboard wrap. You hand it over on a Tuesday evening between trains. I did this twice. Both times took an hour of my Saturday and forty minutes of the actual handoff.

The flat-pack disassembly matters. The legs unscrew. The quilt folds into a vinyl bag if you have one (the bag is ¥600 at Nitori). The heating element stays bolted under the tabletop. A standard kotatsu in two parts fits in a Yamanote car at 9pm on a Sunday. It does not fit in a rush hour train ever.

A new kotatsu disposed through 粗大ごみ at end-of-stay is ¥1,200 to ¥1,800 in most central wards. You buy a sticker at the konbini. You attach it to the table. You leave it on the curb on the assigned date. The dates are 1 to 4 weeks out from the call to the ward office. Setagaya gives you 14 days. Shibuya gives you 21. Don't arrange this in week 11 and you have a kotatsu you cannot legally leave behind on departure day.

This is the part the listicle never mentions.

The 1LDK changes the answer

In a 1K, the kotatsu earns its place. It doubles as a desk, a place to eat, and the only place to sit in the evening. Three functions on one piece of furniture in a 22m² apartment.

In a 1LDK with a real couch in the living room, the kotatsu loses two functions. You eat at the kitchen table. You sit on the couch in the evening. The kotatsu becomes a third piece of furniture without a clear use. It sits in a room you barely use. Across three months in a 1LDK, I have never seen a stayer actually use one well. They become a place to dump laundry.

The math flips here. In a 1LDK, the heater wins all four tasks. The kotatsu becomes furniture you bought to honor the listicle.

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What 90 days teaches you about both

Late January is the kotatsu hour. The streetlight outside the window is yellow on the wall by five-thirty. The room is 14°C. The aircon makes a small grumble at the defrost cycle. You have moved a chair to the corner because the corner is warmest. The sky is dark before you've started cooking.

If the room has a kotatsu, you turn it on. You eat at it. You read at it. You fall asleep at it once a week. You wake up at 1am with your neck at the wrong angle. The 90 days inside the kotatsu are slower in a way that matters.

If the room has no kotatsu, you cook. You eat at the table. You take the heater into the bathroom for five minutes before your shower. You turn it off. You sit at the desk with a blanket across your lap. The 90 days are the ward's January. The apartment is a place you sleep and work, not a place you settle in.

The right answer depends on which kind of January you want from the stay.

What I'd actually buy

For a 90-day stay in a 1K, December through February, planning evenings at home: buy a used kotatsu on Mercari for ¥3,000 to ¥6,000 in early December. Add a ¥3,800 ceramic heater for everything else. Total spend ¥7,000 to ¥10,000. End-of-stay: list the kotatsu on Mercari in week 11. Hand it off at a station in week 12. Throw the heater in 粗大ごみ. Carry it home if your luggage allowance is generous.

For a 90-day stay in a 1LDK, or a 1K where you work long hours and are out most evenings: skip the kotatsu. Buy the ceramic heater only. The kotatsu's evening hours don't compound for you.

For a 60-day stay or shorter in any layout: skip the kotatsu. The aircon and a single ¥3,800 heater clear the four tasks. A kotatsu under 60 days does not pay back the hour of the Mercari handoff.

The shape of the winter

By February you stop comparing the appliances. The kotatsu is a piece of furniture or it isn't. The heater stands by the bathroom door either way. The 14°C room is the room you live in for January and February, regardless of which seat is warm.

What changes between 30 days and 90 days in winter is whether you arrange the apartment for the season or move through it as a guest. A 30-day stayer treats the room as borrowed. A 90-day stayer rearranges. The kotatsu is the most committed rearrangement. You move the existing low table out of the way. You lay down a thicker rug. You stop using the desk for an hour every evening, because the laptop has moved to the floor.

That's not a heating choice. That's a relationship to the season.

For more on what the heating side looks like (aircon costs, kerosene rules, the January electricity math), see Tokyo apartment heating and mold, the resident rules.