1. Reduce the average temperature difference. This can be achieved by
    turning thermostats down (or, if you have friends in high places, by
    changing the weather).
  2. Reduce the leakiness of the building. This can be done by improving
    the building’s insulation – think triple glazing, draught-proofing,
    and fluffy blankets in the loft – or, more radically, by demolishing the
    building and replacing it with a better insulated building; or perhaps
    by living in a building of smaller size per person. (Leakiness tends
    to be bigger, the larger a building’s floor area, because the areas of
    external wall, window, and roof tend to be bigger too.)
  3. Increase the efficiency of the heating system. You might think that
    90% sounds hard to beat, but actually we can do much better.

Cool technology: the thermostat

The thermostat (accompanied by woolly jumpers) is hard to beat, when it
comes to value-for-money technology. You turn it down, and your building
uses less energy. Magic! In Britain, for every degree that you turn the
thermostat down, the heat loss decreases by about 10%. Turning the ther-
mostat down from 20 °C to 15 °C would nearly halve the heat loss. Thanks
to incidental heat gains by the building, the savings in heating power will
be even bigger than these reductions in heat loss.

Unfortunately, however, this remarkable energy-saving technology has
side-effects. Some humans call turning the thermostat down a lifestyle
change, and are not happy with it. I’ll make some suggestions later about
how to sidestep this lifestyle issue. Meanwhile, as proof that “the most
important smart component in a building with smart heating is the occupant,”
figure 21.2 shows data from a Carbon Trust study, observing the
heat consumption in twelve identical modern houses. This study permits
us to gawp at the family at number 1, whose heat consumption is twice
as big as that of Mr. and Mrs. Woolly at number 12. However, we should
pay attention to the numbers: the family at number 1 are using 43 kWh
per day. But if this is shocking, hang on – a moment ago, didn’t I estimate
that my house might use more than that? Indeed, my average gas
consumption from 1993 to 2003 was a little more than 43 kWh per day (fi-
gure 7.10, p53), and I thought I was a frugal person! The problem is the
house. All the modern houses in the Carbon Trust study had a leakiness
of 2.7 kWh/d/°C, but my house had a leakiness of 7.7 kWh/d/°C! People
who live in leaky houses...

The war on leakiness

What can be done with leaky old houses, apart from calling in the bull-
dozers? Figure 21.3 shows estimates of the space heating required in old

Figure 21.2. Actual heat consumption in 12 identical houses with identical heating systems. All houses had floor area 86 m2 and were designed to have a leakiness of 2.7 kWh/d/°C. Source: Carbon Trust (2007).