Saving electricity at home in winter: air-conditioner settings, filters, windows, kotatsu and standby power

The short answer

The quickest way to save electricity in winter is to start with heating. According to the Government of Japan's public relations site, heating, including air conditioners, accounts for about 30% of household electricity use in winter, and about 60% of the heat lost from a heated home escapes through windows and other openings.

Start with three things: set the air conditioner to around 20°C and clean its filter once or twice a month; cover windows with thick, full-length curtains; and turn kotatsu and electric carpets down to "medium". These cut electricity use without making you put up with the cold.

Air conditioners: temperature and filter

The Agency for Natural Resources and Energy's energy-saving portal estimates that lowering the heating setting by 1°C saves 15.80 kWh, or about 490 yen, a year on a 2.5 kW air conditioner, and 45.20 kWh, or about 1,400 yen, on a 4.0 kW unit. Comparing a clogged filter with one cleaned once or twice a month gives a difference of 37.90 kWh, or about 1,170 yen, a year on a 2.5 kW unit.

These yen figures assume electricity costs 31 yen per kWh including tax. The model is a south-facing wooden house in Tokyo, with a heating season of 169 days from 28 October to 14 April. If your contract rate is different, so is the saving, so substitute the unit price shown on your electricity bill.

Running the heating one hour less per day saves 35.68 kWh, or about 1,110 yen, a year on a 2.5 kW unit. Other tips include leaving temperature control to the automatic mode instead of switching on and off repeatedly, angling the airflow downward so warm air reaches your feet, and keeping the outdoor unit's vent clear.

Keep heat in with windows and curtains

Because so much heat escapes through windows, what you do around them directly affects how well your heating works. The government site suggests thick, long curtains, insulating sheets or film on the glass, and secondary glazing. The energy agency also notes that curtains reaching the floor work better.

Open the curtains during the day to let sunlight in, and close them at night to hold the warmth. Opening doors and windows less often is basic, too. In rooms where you use a fuel-burning heater such as a kerosene stove, however, you still need to ventilate regularly.

Kotatsu and electric carpets: "medium" and layering

By the energy agency's estimate, turning an electric kotatsu from "high" to "medium" saves 48.95 kWh, or about 1,520 yen, a year at five hours a day. Using an extra top cover and an under-futon with the kotatsu quilt saves 32.48 kWh, or about 1,010 yen, compared with the quilt alone.

For a carpet sized for three tatami mats, turning it from "high" to "medium" saves 185.97 kWh, or about 5,770 yen, a year. Choosing a size that fits the room, a two-mat carpet instead of a three-mat one, saves 89.91 kWh, or about 2,790 yen. Laying an insulating mat underneath helps, and if the carpet can heat sections separately, switch off the parts nobody is using. A kotatsu mainly warms you from the waist down, so adding a layer on top lets you keep the setting low.

Standby power and lighting

A TV switched off with the remote still uses power. The energy agency advises turning off the main power switch, and unplugging when you are away for a long time, such as on a trip.

For lighting, swapping a 54 W incandescent bulb for a 7.5 W LED bulb saves an estimated 93.00 kWh, or about 2,880 yen, a year at 2,000 hours of use. Light fittings lose 5 to 15% of their brightness a year to dirt, so cleaning them helps as well. Winter nights are long and lights stay on longer, so switching off lights in empty rooms is an easy place to start.

Things to keep in mind

All the figures here are estimates based on specific appliances and patterns of use. Results vary with your region, your home's insulation and the age of your appliances. Putting up with too much cold can harm your health, so before lowering the room temperature, look at filters, curtains and clothing first.