Every year, sometime in late November, it happens. A guest from Germany or Canada messages us at 11pm: “The apartment is freezing. Is the heating broken?” Almost every time, the heating works fine. They’re just meeting Japanese housing in winter for the first time: no central heating, single-pane windows, and a remote control written entirely in kanji.

October is the right time to get ready. It’s still mild enough that nobody’s complaining, and contractors aren’t booked solid yet. Here’s how we think about winter at our properties: heating, condensation, and the questions you can answer before guests have to ask them.

TL;DR

  • Most Japanese homes heat one room at a time instead of the whole building, and many older ones have poor insulation, so guests from countries with central heating are often caught off guard.
  • In most guest units, a wall-mounted air conditioner in heating mode should be the main heat source. Test every unit and clean the filters before the first cold week.
  • In our units we avoid unvented kerosene and gas heaters. The fire and carbon-monoxide risk with guests who’ve never used one isn’t worth it.
  • Condensation (結露) and mold are the hidden winter cost. Windows, closets on exterior walls, and futons on the floor need attention at every turnover.
  • Most heating messages come from a handful of questions: which button means heat, how hot the water gets, and whether the vent can be switched off. Answer them in the house manual and on stickers.

Why Are Japanese Rentals So Cold in Winter?

Japanese rentals feel cold because most homes heat individual rooms only while someone is in them, rather than keeping the whole building warm. Many older apartments and wooden houses also have single-glazed aluminum window frames and little wall insulation. As soon as the air conditioner turns off, the heat leaks out.

That’s normal for Japanese residents. A guest who grew up with radiators in every room, set to 21°C all winter, will read it as a fault. Hallways, toilets and bathrooms that are never heated make the gap worse. Usually it isn’t that the heating is weak. It’s that it works differently from what the guest is used to.

What Heating Should You Actually Provide?

For most Tokyo, Osaka and Kyoto units, the main heat source should be a reversible air conditioner (エアコン) in heating mode (暖房). It’s efficient, it’s already on the wall, and guests can run it safely. If you only do one thing this month, switch every unit to heating mode and run it for 30 minutes. A unit that cools perfectly in summer can still fail at heating, and you want to find out now rather than from a guest in December.

Our checklist:

  • Clean the filters. A clogged filter cuts heating output noticeably, and units that haven’t been cleaned since summer often smell musty the first time they heat.
  • Check that bedrooms are covered. If a sleeping area has no unit of its own, we add an oil-filled radiator or a ceramic heater with tip-over and overheat cut-offs.
  • Avoid unvented kerosene and fan heaters in guest units. They’re common in Japanese homes, but guests don’t know how to refuel them or that the room needs airing, and the fire risk is real. Check your insurance policy too. Some policies take a hard line on open-flame heaters.
  • Kotatsu are charming but optional. Guests love them. If you provide one, make sure it has an auto-off timer, and put a note in the manual not to sleep under it.

How Do You Stop Condensation and Mold?

The way to stop condensation is to cut moisture at the source and give it a way out: ventilate, dehumidify, and keep air moving behind furniture and under bedding. Warm indoor air hits cold single-pane glass, and by morning the window sills are wet. Leave that alone for a few weeks and you get black mold on the window frames and curtains, and inside closets on exterior walls.

What we do:

  • Wipe the windows and sills at every turnover. We added this to the cleaning checklist, and it takes two minutes.
  • Put insulating window film (断熱シート) on the worst windows. It’s cheap, it comes off cleanly, and it noticeably cuts condensation on single glazing.
  • Lift futons off the floor. Slatted すのこ bases underneath, and futons dried out during turnovers. Moisture under a futon is the fastest route to a mold complaint.
  • Run a dehumidifier in problem rooms between guests, especially ground-floor units.
  • Keep the 24-hour ventilation (24時間換気) on. Guests switch it off because it feels like it’s letting cold air in. A small sticker explaining why it should stay on helps.

Leave a small gap between furniture and exterior walls, too. Mold you find behind a wardrobe in March costs far more than moving it 5cm in October.

What Will Guests Ask About Heating?

Most winter heating messages come down to the same few questions. In our own message logs, the same few heating questions keep coming back, especially during the first genuinely cold week of the season.

  • “Which button is heat?” Remotes say 暖房, 冷房 and 除湿 in kanji. We put a small English label next to each button.
  • “Why is the shower lukewarm?” The water-heater panel (給湯器) sets the temperature, and guests don’t know where it is. Photograph it for the house manual.
  • “Can I turn off the vent?” (See above.)
  • “Is the toilet seat supposed to be warm?” Yes. Explain the controls so nobody unplugs it.

We put all of this in the house manual, and the AI concierge we run answers from those same property details, so at 11pm a guest can usually get a relevant answer from the current house-manual data without waiting on us. The format matters less than doing it before the first cold night.

What About Cold Regions and Frozen Pipes?

In Hokkaido, Tohoku, Nagano and other cold areas, frozen pipes are the biggest winter risk, and they cost far more to fix than any guest complaint. Many local homes have a water-drain procedure (水抜き) for nights when the place is empty. If your property has one, write it down clearly for your cleaners, and get a local contractor to confirm the steps for that specific building. Guidance from Tokyo doesn’t transfer. If you’re booking quotes for insulating pipes or replacing water heaters, get them early. Autumn is when local contractors’ calendars fill up.

Does Winter Heating Change Your Pricing?

Yes, a little. Heating can push winter electricity bills noticeably higher, especially in poorly insulated units where guests run the AC around the clock. We don’t add surcharges. We just factor it into winter rates and minimum stays, and ask guests in the manual to turn the heating off when they head out for the day. Most do.

FAQ

Q: Should I leave the heating on between guests?

Normally no in mild regions. Turn it on 30–60 minutes before check-in if you have smart control, or ask cleaners to switch it on at the end of their turnover. In freezing regions, low background heat or a proper water-drain procedure protects the pipes.

Q: Are kerosene heaters acceptable in a short-term rental?

Kerosene heaters are not banned outright nationwide, but using fire appliances is subject to local fire-prevention ordinances, the property’s classification under the Fire Service Act (消防法), your insurer’s rules, and building rules. Confirm with the local fire department and your insurer before you provide one. We don’t put them in guest units because guests are unfamiliar with refueling and ventilation. If you do provide one, give clear written instructions.

Q: What’s a low-cost first fix for window condensation?

Insulating window film, plus wiping the sills at every turnover. Together they cost very little and prevent most of the mold damage we used to see.

This article is general operational information, not legal, tax, insurance, or fire-safety advice. Requirements vary by municipality, building, license type, and insurance policy; confirm with your local fire department, licensing authority, insurer, and qualified professionals.