Turning off my boiler at night? (Silly question perhaps)

lithopsian

The basic premise is quite simple: the cooler your house the less power it takes to heat it. So yes, turning off, or down, your heating when you don't need it warm will save you money.

The details are much more tricky. There is an insidious idea promoted by various parties that having heating "on" all the time is the best way to go. This has its basis, as do many urban myths and old wives' tales, in some actual facts but has led to unfortunate ideas such as that you should keep your house at 22C 24/7 or you are somehow wasting energy by making the boiler fire at full power to re-heat everything. Some parties appear to me to take this further and explicitly recommend such foolish ideas, perhaps for their own benefit.

Modern boilers are most energy efficient when running at relatively low power for long periods, although the actual difference is a few percent at best. This can be compounded by the over-run effect where hot radiators and high-hysteresis thermostats cause room temperatures to overshoot to unnecessarily warm temperatures, but again it should be a very small effect unless you are sweating in the heat and then freezing an hour later. The non-trivial amount of electricity it takes for a typical central heating system to operate can easily swamp these savings if you start trying to run your heating continuously at 1kW or even less. This is all added to by electronic heating controls that often don't even have an "off" settings, just periods of warmer or cooler temperatures, as if the heating being off was somehow evil.

Well-insulated homes maintain the temperature of their masonry and fittings for a very long period, certainly many days to cool down to near the outside temperature. Similarly, it all takes a long time to heat up again if you let it get really cold, especially if the only way it can warm up is by being in contact with moderately warm air. This is one basis of the "keep it constantly warm" brigade's ideas, possibly combined with the condensation that can occur in some situations if you combine warm air with cold fittings. It is also (one of the things) behind that feeling of chill you get when a house has been allowed to get really cold and even though the thermometer says it is back to 22C you don't feel it because the furniture and walls are still all quite a but colder.

An even more tricky thing is that human beings are not thermometers and they don't need the same temperature all the time. You may be comfortable doing some sort of physical work at 14C but might equally be too cold sitting for many hours at 20C, and that's just one person. An older or ill person might be cold at 22C. Don't feel like the heating has to be on just because some computer tells you so.

So as with all things, work in moderation. Don't feel you need to turn off your heating every time you step outside for five minutes, but equally don't be conned by the idea that leaving your heating on when you're not there is in any way energy or cost efficient. Certainly if the house is unoccupied all day you don't need to keep it heated to the temperature that you would want when you sit down in front of the TV, and you'd be mad to heat it to those temperatures while you were off skiing for a fortnight.