new heating controller that allows me to set different target temperatures
for different times of day. With these changes, my consumption decreased
from an average of 50 kWh/d to about 32 kWh/d.

This reduction from 50 to 32 kWh/d is quite satisfying, but it’s not
enough, if the aim is to reduce one’s fossil fuel footprint below one ton of
CO2 per year. 32 kWh/d of gas corresponds to over 2 tons CO2 per year.

In 2007, I started paying more careful attention to my energy meters.
I had cavity-wall insulation installed (figure 21.5) and improved my loft
insulation. I replaced the single-glazed back door by a double-glazed door,
and added an extra double-glazed door to the front porch (figure 21.6).
Most important of all, I paid more attention to my thermostat settings.
This attentiveness has led to a further halving in gas consumption. The
latest year’s consumption was 13 kWh/d!

Because this case study is such a hodge-podge of building modifications
and behaviour changes, it’s hard to be sure which changes were the
most important. According to my calculations (in Chapter E), the improve-
ments in insulation reduced the leakiness by 25%, from 7.7 kWh/d/°C to
5.8 kWh/d/°C. This is still much leakier than any modern house. It’s frus-
tratingly difficult to reduce the leakiness of an already-built house!

So, my main tip is cunning thermostat management. What’s a reason-
able thermostat setting to aim for? Nowadays many people seem to think
that 17 °C is unbearably cold. However, the average winter-time tempera-
ture in British houses in 1970 was 13 °C! A human’s perception of whether
they feel warm depends on what they are doing, and what they’ve been
doing for the last hour or so. My suggestion is, don’t think in terms of a ther-
mostat setting
. Rather than fixing the thermostat to a single value, try just
leaving it at a really low value most of the time (say 13 or 15 °C), and turn
it up temporarily whenever you feel cold. It’s like the lights in a library.
If you allow yourself to ask the question “what is the right light level in
the bookshelves?” then you’ll no doubt answer “bright enough to read the

Figure 21.4. My domestic gas consumption, each year from 1993 to 2007. Each line shows the cumulative consumption during one year in kWh. The number at the end of each year is the average rate of consumption for that year, in kWh per day. Meter-readings are indicated by the blue points. Evidently, the more frequently I read my meter, the less gas I use!
Figure 21.5. Cavity-wall insulation going in.
Figure 21.6. A new front door.