Device power time
per day
energy
per day
Cooking
– kettle 3 kW 13 h 1 kWh/d
– microwave 1.4 kW 13 h 0.5 kWh/d
– electric cooker (rings) 3.3 kW ½ h 1.6 kWh/d
– electric oven 3 kW ½ h 1.5 kWh/d
Cleaning
– washing machine 2.5 kW 1 kWh/d
– tumble dryer 2.5 kW 0.8 h 2 kWh/d
– airing-cupboard drying 0.5 kWh/d
– washing-line drying 0 kWh/d
– dishwasher 2.5 kW 1.5 kWh/d
Cooling
– refrigerator 0.02 kW 24 h 0.5 kWh/d
– freezer 0.09 kW 24 h 2.3 kWh/d
– air-conditioning 0.6 kW 1 h 0.6 kWh/d

### Hot clothes and hot dishes

A clothes washer, dishwasher, and tumble dryer all use a power of about
2.5 kW when running.

A clothes washer uses about 80 litres of water per load, with an energy
cost of about 1 kWh if the temperature is set to 40 °C. If we use an indoor
airing-cupboard instead of a tumble dryer to dry clothes, heat is still required
to evaporate the water – roughly 1.5 kWh to dry one load of clothes,

Totting up the estimates relating to hot water, I think it’s easy to use
about 12 kWh per day per person.

## Hot air – at home and at work

Now, does more power go into making hot water and hot food, or into
making hot air via our buildings’ radiators?

One way to estimate the energy used per day for hot air is to imagine
a building heated instead by electric fires, whose powers are more familiar
to us. The power of a small electric bar fire or electric fan heater is 1 kW
(24 kWh per day). In winter, you might need one of these per person to
keep toasty. In summer, none. So we estimate that on average one modern
person needs to use 12 kWh per day on hot air. But most people use more
than they need, keeping several rooms warm simultaneously (kitchen, living
room, corridor, and bathroom, say). So a plausible consumption figure
for hot air is about double that: 24 kWh per day per person.

This chapter’s companion Chapter E contains a more detailed account
of where the heat is going in a building; this model makes it possible to

Table 7.4. Energy consumption figures for heating and cooling devices, per household.
Figure 7.5. The hot water total at both home and work – including bathing, showering, clothes washing, cookers, kettles, microwave oven, and dishwashing – is about 12 kWh per day per person. I’ve given this box a light colour to indicate that this power could be delivered by low-grade thermal energy.
Figure 7.6. A big electric heater: 2 kW.