Heating Advice - Always on low or blast on high?

oaks321

Morning,

First post (long time reader) so go easy

Me and my girlfriend live in a smallish flat in London, we're on the 2nd floor in a purpose built block of flats, and only have one external wall. We have a flat beneath and behind us, an office to the right of us and the stairwell/corridor to the left of us. We're on the top floor so have a loft, which seems relatively well insulated.

We have four windows, all of which are triple glazed (double glazing on the 'outside', a 6 inch gap and then single glazing on the 'inside').

My question is, what's the most efficient way to heat the flat? We have an open plan kitchen/living space, with one radiator. A hallway (one radiator) leads from the kitchen/living space to the front door, and off the hallway we have a bedroom (one radiator), a small study (one radiator) and a small bathroom (heated towel rail).

The flat generally holds the heat quite well, and we do things like leave the oven door open after we've finished cooking (thanks MSE!) to help distribute heat rather than turn the heating on. However, it's starting to get too cold and we feel we're getting to the point where we need the heating on (not had it on since Feb this year :cool:)

The heating is controlled by a thermostat in the living room/kitchen, and the boiler is a modern combi boiler. So my question, that I've asked in a very long winded way, is, would we be better to have the thermostat set to about 18 degrees, so there's a low, but pretty much constant heat coming out of the radiators, or have the heating off until we're freezing, turn the thermostat up to say 25 or something, so that the flat gets really warm and toasty quickly, and then turn the heating off again until the next time we're freezing?

Which would you choose? and which is likely to lead to the lowest gas bill?

Thanks for reading this rather wordy first post!

HappyMJ

Why do people think that turning the thermostat to 25 makes it heat up quicker than just turning it to 18?

oaks321

Well unless I was imagining it, when we moved in lat Jan this year, we had the thermostat on 18 for a few days and the radiators were only ever lukewarm, when it got serious cold I turned it up to 25 and the radiators got seriously hot (not touched the controls actually on the radiators)

But even if I did imagine it, and it's something I need to control via the boiler rather than thermostat, your response wasn't the most helpful in answering the question, but thanks for trying

Cardew

Welcome to the forum.

The temperature of the water in the radiators is not affected in any way by the wall thermostat. If your flat was at, say, 10C and you put the thermostat at 15C, 20C or 25C the radiators would get to exactly the same heat as the water temperature would be the same. When the room reached 15C the boiler would shut off, but the rate at which it went from 10C to 15C would be the same regardless of the thermostat setting.

The water temperature is set on your combi boiler - that is both water for baths etc and the radiators.

Turning to your question there is no answer. To illustrate:

If I asked you which took the shortest time to drive from London to Glasgow:

A. Drive at a steady 30mph with no stops.

B. Drive at 100mph with stops.

Could you give an answer without knowing the length of the stops?

In the same way, it is impossible to say what is cheaper with heating -

A. Temperature a steady 18C

B. Temperature at 25C in bursts

As a general principle the lower you have your heating the cheaper, and the longer switched off the cheaper.

oaks321

Thanks for your reply Cardew,

I understand that to an extent it's a 'how long is a piece of string question', I guess I was just hoping that there may be some people on here with personal experience of a broadly similar situation.

macman

oaks321 wrote: »

Thanks for your reply Cardew,

I understand that to an extent it's a 'how long is a piece of string question', I guess I was just hoping that there may be some people on here with personal experience of a broadly similar situation.

It's not a 'how long is a piece of string question'? The longer you leave the heating on and the higher you set it, the more it will cost you-end of story.
If you do a forum search then you will see that (with the onset of winter) this question is asked many times each week-yet the answer is always the same.
If you ask 'which method is more comfortable', that of course is an entirely different question. Your given options are the two extremes. 18C is too cold and 25C too hot for most people. Try using the timer/programmer as intended and set the room stat to around 20C to start with. Experiment from there and adjust the local temp with the TRV's.

bengasman

Cardew wrote: »

The water temperature is set on your combi boiler - that is both water for baths etc and the radiators.
Turning to your question there is no answer.

Nonsense. There is an answer and it is very simple and straightforward.
The lower you set the temperature of the boiler, the more efficient it will work. The big threshold is at the return temperature of 55 degrees Celsius. Go a few degrees above, and the efficiency drops noticeably. Go further below about 52, and the efficiency only goes up slowly.

The greater the difference between outdoor temperature and roomstat temperature, the long the boiler will fire to achieve that and thus it is more expensive.

The longer you have the boiler on to maintain a temperature difference, the more it will fire which again will cost more.

Cardew

bengasman wrote: »

Nonsense. There is an answer and it is very simple and straightforward.
The lower you set the temperature of the boiler, the more efficient it will work. The big threshold is at the return temperature of 55 degrees Celsius. Go a few degrees above, and the efficiency drops noticeably. Go further below about 52, and the efficiency only goes up slowly.

The greater the difference between outdoor temperature and roomstat temperature, the long the boiler will fire to achieve that and thus it is more expensive.

The longer you have the boiler on to maintain a temperature difference, the more it will fire which again will cost more.

It really would help if you read(and understood!) the question and my reply, instead of going off at a tangent!

Just to remind you, this was the OP's question:

So my question, that I've asked in a very long winded way, is, would we be better to have the thermostat set to about 18 degrees, so there's a low, but pretty much constant heat coming out of the radiators, or have the heating off until we're freezing, turn the thermostat up to say 25 or something, so that the flat gets really warm and toasty quickly, and then turn the heating off again until the next time we're freezing?

Which would you choose? and which is likely to lead to the lowest gas bill?

It would also help if you didn't litter MSE with provocative posts - 'rubbish - nonsense etc - you are just showing yourself up!

oldtractor

I would get thick thermal lined curtains up at the windows, keep internal doors shut as much as possible and heat to a constant 18 degrees during the day whilst you are home. at night I would set the thermostat to 15 or 16 degrees and the same whilst you are not home. I use the "boiling the kettle "principal. It takes a lot of energy to raise the temp of the water from very cold to boiling,but not much from hot to boiling. Also if you are constantly warm you wont need the temp to be 25 degrees just to feel warm enough to stop shivering. 18 all the time will feel better than25 sometimes and perishing cold at others.
Hope this helps.

victor2

The thermostat temperature controls the room temperature at which the central heating will be told that enough hot water has been pumped round the radiators. With it set very high, that temperature will never be reached, so the heating will be pumping hot water round constantly. Until the set temperature is reached, the radiators will be at the temperature your heating system can provide, unless there are separate thermostatic valves on your radiators.
It has been stated on here many times, but if your heating is on, even at a low temperature, it will be burning gas and costing you money. Just set the timer to make the house comfortable by the time you get up and arrive in from work. Consider a programmable thermostat if you want to get a little more sophisticated, so that you can set certain temperatures for different times of the day.

HappyMJ

oldtractor wrote: »

I would get thick thermal lined curtains up at the windows, keep internal doors shut as much as possible and heat to a constant 18 degrees during the day whilst you are home. at night I would set the thermostat to 15 or 16 degrees and the same whilst you are not home. I use the "boiling the kettle "principal. It takes a lot of energy to raise the temp of the water from very cold to boiling,but not much from hot to boiling. Also if you are constantly warm you wont need the temp to be 25 degrees just to feel warm enough to stop shivering. 18 all the time will feel better than25 sometimes and perishing cold at others.
Hope this helps.

I can use the boiling the kettle principal too. It uses a lot of electricity to keep a kettle warm. Do you keep your kettle (or more accurately an urn with an energy saving keep hot function such as http://www.google.co.uk/products/catalog?q=urn&oe=utf-8&rls=org.mozilla:en-GB:unofficial&client=firefox-a&um=1&ie=UTF-8&tbm=shop&cid=315835383687873975&sa=X&ei=mSjVTr-2JsWK8gOStrWHAg&ved=0CH8Q8wIwBg) set to the keep warm seeting so that you can get a cup of tea whenever required? No because it costs too much.

That urn is perfect for an office as the cost of labour is more than the cost of electricity but you will usually find they are turned off at night and weekends to save electricity.