Power use and Heat

So fine, I live in the UK too. If you have a whole house on a single thermostat that usually
means you're using gas central heating. In which case heating your house by leaving a PC
turned on is already horribly inefficient because of the price difference between gas and
electricity. You also live in a temperate country, where the house doesn't need to be heated
for most of the year (and indeed may be uncomfortably hot for a month or two each summer).

Any radiators installed since the popularity of home central heating in the UK really began
will have bypass valves so that you can disable radiators in unused parts of the house (e.g. a
spare bedroom) or add a cheap local thermostat (included in newer installations) which
bypasses when that room is above a certain temperature. Most installers will skip rooms that
are rarely occupied and can be heated by conduction or convection from elsewhere, such as
closets.

Any installation that's less than 30 years old will have a timer as well as the thermostat and
manual control, and newer ones will have a seven day variable timer. Typically this means you
only heat the house for a few hours every day, usually when you wake up (it's not nice to wake
in a cold house, and the timer may also control production of stored hot water for the
bathroom) and for a while in the afternoon or evening. There's no need to heat the house while
you're asleep, you will be comfortable at a lower temperature and the bedding insulates you
anyway.

The idea that all heat energy released by inefficient use is "free heating" in some way just
doesn't work out in reality. Unless you've got an electric element or fan heater next to the
PC that you leave switched on all the time, chances are that turning the PC off is a
significant net saving (I tend to work to £1 per watt as a rule of thumb).