To think keeping thermostat at 20 will cost the same as keeping it at 17?

[Cigent]

I know it's said that turning the heating down a few degrees will save money, but how?

If I'm, say, October I set the heating to 20 degrees and leave it like that, and if it falls to 19 degrees it automatically kicks in until the house is up to 20 then switches off, how would that cost any more than keeping it at 17 and it kicking in when it dropped to 16 to heat the house one degree? In both cases it's only kicking in to heat the house by one degree, so how does keeping it lower cost less money?

I understand that if I turn it on when the house is at, say 15 degrees, then it would cost more to get to 20 than 17, but once it's there surely it would be the same to keep it there?

Good idea to run a 2 week experiment OP!

If you measure the energy use and keep a record of the outside temperature you will be able to calculate the heat loss co efficient of the house!

Rain makes a massive difference depending on the house construction i.e. a single skin Victorian house will lose heat much faster when it rains because the bricks get wet.

Wind will also make a huge difference depending on how "leaky" the house is.

But, if your house is modern cavity construction, well insulated, and relatively airtight then it might well show consistent performance tied closely to the outside air temp.

I totally get the ‘don’t heat a room you’re not using’ thing but is there any benefit to only having one radiator on in a room that currently has two radiators? Intuitively, I don’t think so as the one ‘working’ radiator will need to work harder / be on longer to heat the space. Is that right?

If you are switching off radiators anywhere be careful rhose eooms don't get damp.

Another valuable tip is turning down the flow temperature from the boiler. This makes the boiler work more efficiently (so even though the heating is on for longer it is gentler, and in total you use less gas , because you are catching the heat that would otherwise be lost out of the boiler flue).

There are some explanations at this link www.theheatinghub.co.uk/mission

Because the boiler has to work more to keep it at 20 as it is cold outside? Something like that.

Radiators work by circulating hot water through them so if you shut off a trv or turn down a trv then no no or less hot water will enter that radiator. When the radiator is full of circulating hot water the water the more it circulates the more heat it loses as that radiator uses radiant energy to transfer heat to the air so if you shut down or turn down a radiator it uses less so your boiler doesn’t have to fire up so often to maintain the water to the tempture that you have set you flow rate to.

Jesus christ.

Yes, I’m amazed that’s people don’t understand this….!

in the OPs example, she needs to be comparing the inside temperature to the outside temperature. If it’s 10 degrees outside and she wants it to be 17 degrees inside she’s got to raise it by 7 degrees. At 20 degrees inside she needs to raise it by 10 degrees, which is as near as damn it 50% more. So, even in a vacuum it’d cost 50% more to get it up to 20 degrees in the first place. But it’s not in a vacuum, and will cool down quicker from 20 to 19 degrees than it will from 18 to 17, so the boiler will also be coming on more often to maintain 20 than 18 degrees.

You could save a lot by using a timer - you really don't need the temperature at 20 or even 17 overnight. Let it go off overnight, set it to come on again before you wake, then have it on17 during the day.

Yes, I’m amazed that’s people don’t understand this….!

I’m not.

I thought ValerieDoonican‘s tall glass with a small hole analogy was very good.

‘Scienceplaining’? I can’t tell whether you’re trolling or not. You sarcastically implied that my original comment about houses not existing in a vacuum (perfect insulator) was dumb because I clearly hadn’t considered the fact that insulting houses is a thing. I pointed out that housing insulation is not perfect and can never be perfect because we need to breathe. And now you’re annoyed because you think I’m a scientist explaining things to non scientists? Or you’re actually an expert at this and your sarcasm threw me off and you’re annoyed I think you don’t know the difference between good housing insulation and a vacuum? This is an OP literally asking strangers on the internet for help understanding a physics question. The whole point is the ´scienceplaining’.

I have a hive system which records when the central heating is kicking in and for how long. So you can see at a glance how much harder the system needs to work to achieve the same indoor temperature relative to the changing outdoor temperature.

Scienceplaining’? I can’t tell whether you’re trolling or not. You sarcastically implied that my original comment about houses not existing in a vacuum (perfect insulator) was dumb because I clearly hadn’t considered the fact that insulting houses is a thing

I didn't respond to your comment at all.

My comment about insulation was a general comment about the whole OP and turning down the thermostat, keeping the house room.

I didn't quote you or even @ you

In fact - sorry, I can see that I was quoting you - but it was meant to be supporting you, not being sarcastic

It was meant to be supportive of your comment, and a general observation on the benefit of insulating a house to reduce heat loss.

Because - as you correctly said - losing heat and the outside temperature is important - and there are benefits to insulating a house so we can reduce the loss of heat to the outside.

That's all.

Erm, isn't it just science?
It is on a thread where explanations about heating and insulation have been asked for.

Interesting @FourTeaFallOut , is that the Hive Heating Plus thing?

It use to be plain old hive but now I think this year they may have bundled it up as a subscription feature. Although my inner geek may stretch to £4 a month this winter.

Thanks - going to try the free trial. Might help with my ongoing campaign to try and get DH to put a jumper on before moaning.

Oh, I see. I misunderstood your three little dots as sarcasm.

You asking the question in order to understand something better is good. But your unwillingness to accept basic science is not.
It's not blind acceptance to listen to and accept actual provable scientific fact. Michael Gove has a lot to answer for.

By all means experiment with your smart meter. Experimenting to see what works is again, a good way to approach questions. But if you're experimenting, the conditions at for each two weeks need to be the same. If two of three weeks are mild outside and two of them very cold, you won't get your answer. Likewise unless your smart meter can differentiate between the fuel used for heating and the fuel used for everything else, your other activities during those experimental periods will also skew the results

I find this all fascinating. I can't stand a too hot house. We have a thermostat upstairs and one downstairs. The heating goes on in the coldest months for about an hour first thing downstairs and again for a couple of hours during the day downstairs when it feels chilly. It's never on anywhere after about 8 at night. Upstairs maybe on for an hour a day if we are having baths. So our house heats up and cools right down several times. Is this more expensive than having it on continuously?

Probably not

I do this too. Our bills are relatively low for a 4 bed detached. I definitely think having a thermostat set to 20 degrees all day is an expensive way to go about things.

We never have heating on during the night. Wouldn't dream of it.

The general truth is that uses less energy to heat up on an as and when basis rather than leaving the thermostat on a static temperature throughout the day. But actually I have found in my own home, having reduced the flow on the boiler which may play a big part, it is roughly the same - not to mention more comfortable - to do the latter but then someone is always home here. If people are all out through the day the former makes more sense.

I'm an engineer. Mechanical, not thermal and did not know this so isn't hugely surprising TBF.

I'm not arguing, given I didn't study thermodynamics, but that doesn't seem logical if the delta T is the same 1 degrees from 20-19 and 18-17. Care to explain in layman's terms why this is?