Tokyo runs hot and sticky in summer and surprisingly cold in winter, and most apartments here have thin walls and no central heating. If your first August feels like a sauna or your first January has you wearing a coat indoors, you are not doing anything wrong. The good news is that the single unit already bolted to your wall handles almost everything, and a few cheap extras and habits cover the rest. Here is how to stay comfortable without a big bill or a safety scare.
Your aircon does both: cooling and heating
The wall-mounted air conditioner (エアコン, eakon) in most Tokyo apartments is a heat pump, which means it both cools and heats. You do not need a separate heater for the unit to do its job. On the remote, look for the mode button: the snowflake or 冷房 (reibou) is cooling, the sun or 暖房 (danbou) is heating, the water drop or 除湿 / ドライ is a dehumidify mode that's handy in the rainy season. Set a comfortable target temperature, let it run, and clean the filters every couple of weeks so it stays efficient. In summer, the government's heatstroke advice is simple: when it is hot, actually use the cooling rather than enduring it, and keep an eye on the room temperature.
Supplementary heat for cold rooms
Aircon heating can struggle to warm a cold room quickly, and the warmth pools near the ceiling. A few inexpensive extras make a big difference:
- Electric fan heater (セラミックヒーター / electric heater): fast, plug-in spot warmth for a bathroom or desk. No combustion, so no ventilation worry, but it draws a lot of power.
- Kerosene or oil heater (石油ストーブ / 石油ファンヒーター): strong, cheap heat that works in a power cut, but it burns fuel indoors and MUST be ventilated regularly.
- Kotatsu (こたつ): a low table with a heater underneath and a quilt over the top. Cozy, cheap to run, and a Japanese winter classic.
- Electric carpet or electric blanket (ホットカーペット / 電気毛布): warms you directly from below or in bed for very little electricity.
One more thing about the cozy options: a kotatsu, an electric carpet or blanket, or a hot-water bottle can cause a low-temperature burn (低温やけど, teion-yakedo) — a burn that builds up slowly when bare skin rests against an only-moderately-warm surface for a long time. It often happens when people doze off. Don't fall asleep pressed against any of these for hours, and don't keep a heat source in direct contact with the same patch of skin all night.
Any heater that burns fuel — a kerosene or oil heater, or a gas heater — releases carbon monoxide (一酸化炭素), which is colorless and odorless, so you cannot smell or see the danger. Ventilate regularly while it is on (open a window for a few minutes, roughly once or twice an hour — check your heater's manual), never refuel it while it is lit, and never leave it running while you sleep. A CO alarm is cheap insurance. Also avoid plugging high-power heaters into a thin extension cord or an overloaded power strip, which is a real fire cause.
Humidity, condensation, and mold
Tokyo's damp climate plus sealed winter rooms makes condensation (結露, ketsuro) almost inevitable — those water droplets on cold windows. Left alone, it feeds mold (カビ) on walls, window frames, and the back of furniture. Aim for around 40 to 60 percent indoor humidity. Wipe condensation off windows in the morning, run a dehumidifier or the aircon's dry mode in muggy weather, open windows briefly each day to swap the air, and pull furniture a few centimeters off exterior walls so air can move behind it. Futons soak up your body's moisture overnight, so air and dry them in the sun or over a rail regularly, or use a futon dryer.
- Is it cheaper to leave the aircon on all day or turn it off when I go out?
- For short trips of an hour or two, leaving it running often uses less power than letting the room get extreme and cooling or heating it back from scratch. For a full day out, turn it off. Cleaning the filters and not over-setting the temperature saves more than fussing over on/off.
- Do I have to ventilate even with an electric heater?
- Electric fan heaters, kotatsu, and electric blankets do not burn fuel, so they produce no carbon monoxide and need no special ventilation. The strict ventilation rule is only for fuel-burning heaters like kerosene, oil, and gas. That said, opening windows briefly each day is still good for humidity and air quality.
- Where do I buy kerosene for an oil heater?
- Kerosene (灯油, touyu) is sold by the can at gas stations and some home centers in winter, and many neighborhoods have a tank truck that drives around. Store it in a proper kerosene container, away from heat, and never put gasoline in a kerosene heater.
- Clean your aircon filters every couple of weeks — clogged filters waste power and weaken both heating and cooling.
- In summer, close curtains against direct sun and use a fan to spread the cool air so the aircon works less.
- In winter, a draft stopper, thicker curtains, and bubble-wrap film on windows cut heat loss cheaply.
- Don't dry laundry directly over or on a heater — it's a leading cause of home fires.
- Keep one window slightly open or run the 24-hour ventilation if your flat has it; sealed rooms breed condensation and mold.
