Choosing and using home heaters: whole room or close to the body, ventilation and running costs

The short answer

Heaters are easier to choose if you think of them in two groups: those that warm the whole room, and those that warm the area close to your body. Air conditioners and kerosene or gas fan heaters warm the whole room; kotatsu tables and electric carpets warm your feet and the space around you.

Then keep two points in mind: fuel-burning heaters need ventilation while they are running, and the cost of an electric heater depends on its power consumption and how long you use it. With those two points clear, it becomes easier to decide how to combine heaters.

Heaters that warm the whole room

An air conditioner uses a heat pump: when heating, it moves heat from the outdoor air into the room. The Agency for Natural Resources and Energy explains that because it moves heat rather than making it, it can heat with less energy. On the other hand, a clogged filter or obstacles around the outdoor unit reduce how well it works.

Kerosene and gas fan heaters burn fuel and warm the room with hot air, so the room needs regular ventilation while they run. The government's public relations site warns that without enough ventilation, oxygen runs short, combustion becomes incomplete, and carbon monoxide levels rise, which can cause poisoning. Fan heaters also use electricity as well as fuel, and the energy agency's estimates show electricity savings separately from the kerosene or gas savings.

In the same estimates, with an outdoor temperature of 6°C, lowering a kerosene fan heater from 21°C to 20°C at nine hours a day uses 10.22 litres less kerosene a year, about 1,210 yen (calculated at 118 yen per litre). Room temperature does not drop suddenly, so the tip is to switch off about 15 minutes before you go out or go to bed. Cleaning the filter is also essential for keeping it efficient.

Heaters that warm the area around you

An electric kotatsu or electric carpet warms the area around the person using it. A kotatsu mainly warms you from the waist down, so wearing one extra layer on top makes it more comfortable. When you use it together with an air conditioner or another heater, keep the kotatsu setting low. With an electric carpet, lay an insulating mat underneath, and if it can heat sections separately, switch off the parts nobody is using.

You can work out the electricity cost of an electric heater as power consumption (kW) × hours of use × unit price of electricity. For example, a 1,000 W heater used for one hour consumes 1 kWh; at the 31 yen per kWh the energy agency uses in its estimates, that is about 31 yen. Check the actual power consumption on the appliance's label or in its manual, and the unit price on your electricity bill. If the heater has high and low settings, noting the wattage of each makes comparison easier.

Circulate warm air and raise the humidity

If your feet stay cold with the heating on, warm air may be collecting near the ceiling. The energy agency and the government site both recommend running a fan or circulator with the heating to move the warm air around, and angling an air conditioner's airflow downward.

The government site also notes that raising the humidity, for example with a kettle or a hot-pot meal, makes the room feel warmer. If you feel cold, check humidity and clothing before turning up the temperature.

Things to keep in mind

The Consumer Affairs Agency warns that hot-water bottles and electric carpets can cause low-temperature burns when the same patch of skin stays in contact for a long time, and asks people not to use them for long periods. It has received a report of a baby laid on a towel over an electric carpet who was suspected of having a low-temperature burn. It also recommends placing floor heaters and humidifiers out of children's reach or surrounding them with a safety gate.

Where to place stoves and how to prevent house fires, and how to stay warm during a blackout without carbon monoxide risks, are covered in detail in the related articles.