*how much* to put up thermostat by one degree?

[The Night Tripper]

Hi all I'm looking for a hand-waving unscientific figure about the cost of heating, along the lines of:

"for every degree you put the thermostat up, you'll pay £xxx extra in heating per week"

This doesn't have to be 'accurate', it's for the purposes of scaring (for their own good) someone who is about to start paying their own bills for the first time.

I realise of course that there are all sorts of variables here, but let's say as a f'rinstance, a two-bedroom flat using electric heating (not sure what type, sorry).

I always ignore these sort of vague statistics when I see them, because they are so clearly unuseful ... and now I want one!

Any pointers?

Cheers J^n

[The Natural Philosopher]

the average outside temp is 9C so every degree above say 15 is 15% increase in bills

needless to say when its -5C outside when you use most fuel, the difference is scarcely noticeable. 5% per degree.

[fred]

In article , The Night Tripper writes

If this is a parent vs child explanation then it'll be wasted breath, the message will come home firmly when they ignore your sage words and get their first bill, although you could soften the blow by taking monthly readings for them (or getting them to do same) and calculating how much their account is falling into arrears behind their DD.

[John Williamson]

Or, to *really* make the point stick, get them on to a pay as you use it account....

That stings them both ways, by paying a higher rate, *and* by making them keep up with usage.

[F]

I've seen a few energy saving ads that suggest you would 'save 10%' for every degree you drop the thermostat by.

No idea on whether or not it's accurate though!

[polygonum]

Obviously nonsensical. :-)

Just think it through by several iterations...

[Martin Brown]

Or put another way the house if it is fairly well behaved and insulated behaves like a fixed value resistor with heat leaking out according to the temperature difference between inside and out.

IOW it costs nothing to maintain a temperature difference of 0C.

deltaT = 1 costs Q deltaT = 2 costs 2Q etc.

If the outside temperature is 9C then maintaining 16C costs 7Q and each extra degree about 14% up or down. Maintaining 25C costs 16C with a one degree change now being about 6%. ISTR the ballpark number used for most premises at 20C or thereabouts is 10% per degree.

Overshooting the target temperature also wastes money and some thermostatic controllers are smarter about this than others.

You actually get a hundred watts for each person inside the house which may support a small postive deltaT with no heating used at all.

Regards, Martin Brown

[F]

Yes, we turned ours down by 11 degrees...

[dennis]

8<

So you are saving 70% then?

[Brian Gaff]

There is also lag and the fact that many thermostats are still electro-mechanical with widely varying amounts of hysteresis.

Brian

[polygonum]

Aha! 11 is obviously the number of the day. (See 11 mph thread.)

Although the statement without qualification could read as saving another 10% of the then current bill for each degree, I prefer to read as did you - another equivalent of 10% of the starting point.

[The Night Tripper]

Thanks - that's a great way to think about it.

Cheers J^n

[Man at B&Q]

Plus heat from other household activity such as cooking. In my second house the pipes from the boiler to the airing cupboard lost so much heat I had to turn the hot water off in the summer for a couple of days at a time to let the house cool down. The cyclinder would stay warm enough for washing and there was s eparate electric shower.

MBQ

[Onetap]

If you want to get all scientific, you probably need to look up 'degree day s', which was how they used to estimate the likely energy consumption of a building in an average year, or work out corrections for energy consumption in real years. The maths is gruesomely tedious.

Otherwise look for a rule of thumb; 4 Btu/hr cu. ft sticks in my mind for some reason.