Keeping central heating on all the time?

heppy23 · 18 September 2006 at 11:54AM

I was chatting to a customer at work who is a plumber.

He said it is cheaper to keep the central heating on 24/7 at a low level rather than having it in bursts as that uses more energy.
(i.e. the boiler uses a lot of energy to heat a cold house up and less just keeping a warm house warm)

I don't think I'd do it as I have to be cold to get to sleep.

Does it make sense?

Cardew · 18 September 2006 at 12:05PM

It makes absolutely no sense whatsoever.

This has been covered time and time again on this forum(do a search) and is an urban myth.

Your plumber might as well suggest that you keep your oven switched on and up to heat all the time; or perhaps keep the kettle/saucepans of water simmering all day. - same principle.

kat21 · 18 September 2006 at 1:19PM

Actually hes spot on right several people I know keep there central heating on low heres the science. when you fire up your boiler, it has to heat up firstly the volumes of each room and then the various surfaces and then the actual structure of the building you live in by maintaining this constant low temperature your not re heating the cold surfaces of your home. Heres how to test, take a reading in the winter for your normal runing of your gas boiler make a note of what your gas meter reading is at the begining of the week then take another reading at the end of the week. The next week repeat the same process but leave the heating on but on a lower setting if you have a good boiler and reasonably good insulation you will be suprised to see that you have infact used less gas. I have triend this many times and it supprised me but, dont take my word for it try it for yourself, do the gas meter readings of your normal weekly run of gas, then try it on a lower setting take the meter readings then you will also know hoiw efficient your home is too
kat21
try it first before commenting

Ken68 · 18 September 2006 at 4:02PM

Hi Hep....don't believe it, what about the new air coming in after opening the door. It might work in a closed situation.Would be nice to see a test tho.

Cardew · 18 September 2006 at 5:18PM

kat21 wrote:

Actually hes spot on right several people I know keep there central heating on low heres the science. when you fire up your boiler, it has to heat up firstly the volumes of each room and then the various surfaces and then the actual structure of the building you live in by maintaining this constant low temperature your not re heating the cold surfaces of your home. Heres how to test, take a reading in the winter for your normal runing of your gas boiler make a note of what your gas meter reading is at the begining of the week then take another reading at the end of the week. The next week repeat the same process but leave the heating on but on a lower setting if you have a good boiler and reasonably good insulation you will be suprised to see that you have infact used less gas. I have triend this many times and it supprised me but, dont take my word for it try it for yourself, do the gas meter readings of your normal weekly run of gas, then try it on a lower setting take the meter readings then you will also know hoiw efficient your home is too
kat21
try it first before commenting

"heres the science" Its not April 1st is it?

Of course you will use less gas if you turn down the temperature on the second week! Turn it off the the third week and you will use no gas! However that wasn't the 'exam question' set by the OP.

The question was does it cost less to have the CH left on permamantly instead of on a timer.

Why do you think they fit timers to every CH system?

Check the Energy Saving Trust. Check any Home energy Advisor.

Quite seriously if your science is correct, why isn't it cheaper to leave your oven switched on and up to heat the whole time, as it will surely cost more to keep heating it up from cold every time you want to use it.

No wonder these urban myths gain credence!!

masonic · 18 September 2006 at 6:21PM

kat21 wrote:

Actually hes spot on right several people I know keep there central heating on low heres the science...

Second law of thermodynamics: The rate of heat loss is directly proportional to the difference in temperature between the two bodies being considered (the house and outside).

Corollary: More energy is therefore lost to the surroundings in a given time if a body is held at an elevated temperature than if it were allowed to cool.

First law of thermodynamics: The more energy lost to the surroundings, the more energy is required to return to that same elevated temperature (or maintain the temperature).

Conclusion: More energy is consumed in maintaining an elevated temperature than allowing a body to cool before reheating it.

It is as simple as that.

kat21 · 18 September 2006 at 7:22PM

Before you shoot your mouths off which you all seem very good at just lately I suggest you go and try it as I did say try it! one week will not hurt try one week as you would normally run the heating system and one week leaving it on a very low setting. This theory works because of the building structure and its ability to store heat, if the building can store heat then the boiler doesnt fire up as much. Please dont shoot off until you try it. I found it very hard to beleive at first but I did a simple trial of one week runing my usual heating cycle and one week of putting the boiler on a very low setting
no mythes, no telling lies it really does work.This is because all buildings take time to get to an optium temperature I am not talking about thermal comfort level I am talking about actually heating the structure of a building first once the buildings structure is heated and maintained the boiler will not fire up as much.
kat21
">First law of thermodynamics: The more energy lost to the surroundings">
more energy is required to return to that same elevated temperature (or maintain the temperature).>
exactly what I was talking about heating the structure and how long it takes to heat that structure, by structure I mean bricks how well the temperature is maintained by those bricks will also make a difference

masonic · 18 September 2006 at 8:19PM

kat21 wrote:

Before you shoot your mouths off which you all seem very good at just lately

Pot > Kettle > Black

kat21 wrote:

This theory works because of the building structure and its ability to store heat, if the building can store heat then the boiler doesnt fire up as much.

So if buildings store heat so well, why don't they just stay at the same temperature without being heated, hmmm?

kat21 wrote:

Please dont shoot off until you try it. I found it very hard to beleive at first but I did a simple trial of one week runing my usual heating cycle and one week of putting the boiler on a very low setting
no mythes, no telling lies it really does work.

Please present your findings to the Nobel prize committee. You have just disproved the law of conservation of energy.

kat21 wrote:

">First law of thermodynamics: The more energy lost to the surroundings">
more energy is required to return to that same elevated temperature (or maintain the temperature).>
exactly what I was talking about heating the structure and how long it takes to heat that structure, by structure I mean bricks how well the temperature is maintained by those bricks will also make a difference

So, if you have a bucket with a hole in it, does it take less water to keep it full all day, or to let it empty in the morning, then refill it in the evening?

kat21 · 18 September 2006 at 8:45PM

ah ha! so,
the bucket theory
hmm, trick question
if you have a light bulb in the middle of the room and you open the door does the light become more or less ?

kat21

Cardew · 18 September 2006 at 8:49PM

Shooting our mouths off?

I think this should be said S L O W L Y in the hope that you read it and, more importantly, understand what is being said.

Firstly it is not in dispute that buildings retain heat and initially it takes more energy to warm the fabric of the building. OK so far?

Secondly it is also not in dispute that turning down the temperature setting for the second week will result in a lower bill than the first week. Still OK?

So this means that the results of your experiment will be exactly as you state. No need for us to try it because we concede that you are correct – Happy so far?

So having got that red herring out of the way, shall we turn to the question that was asked – which had no relevance to the answer you have given us twice.

The Energy Saving Trust is the Government sponsored organisation that deals with most questions concerning energy. Below is a quote:

Question
Is it more economical to leave my heating on 24hrs in the winter?

Answer
No. It is a common misconception that it is cheaper to leave your hot water and heating on all the time. Boilers use more power initially to heat water from cold, however the cost of this is greatly exceeded by the cost of keeping the boiler running all of the time.

The best solution is to programme your heating system so that it comes on when you need it most (possibly early morning and in the evening), and goes off when you don't need it (when you are out of the house or asleep). There are a range of controls that can be used and your heating engineer will be able to provide you with the most appropriate solution.

Depending on your circumstances it may be necessary to keep the heating on all day during winter but it will cost more than if you turn the heating off when you don't need it.

There is provision on their website to comment on any points. If you care to contact them to tell them they are wrong, they will no doubt be grateful and publish a retraction.

Do you not think it vaguely possible that there might be some heat loss from a building? Most structural engineers seem to think so - but what do they know?

masonic · 18 September 2006 at 9:07PM

Cardew wrote:

The Energy Saving Trust is the Government sponsored organisation that deals with most questions concerning energy.

Kat will dispense with that quote in an instant. She's tried it and it works. You wait...

Keeping central heating on all the time?

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