Cheaper to leave CH on 24 hrs?

[reg091]

Thanks for all the input folks. I think there is some confusion over what is meant by "heating being on 24/7".

If a definition of that is the flame burning in the boiler for every second of that 24 hours then there is no argument that that will use more gas than if the flame is extinguished for 16 of those hours.

However, that is not what I was asking. My definition of "heating being on 24/7" is that the flame in the boiler will burn for x number of times in that 24 hour period, whenever it needs to bring the temp back up. Do those times added together equal more or less than the times added together that the flame would be burning if you allowed the system to cool completely several times a day?

Hypothetical example to illustrate: System on for 24 hours = four one minute burns every hour to maintain temp = 96 minutes total burning in a 24 hour period.

System timed to be on for two hours three times a day. Each time it starts from cold it burns for 20 minutes followed by three one minute bursts in that first hour and four in the next. = 27 minutes total burning per two hour timed on session = 81 minutes total burning in a 24 hour period.

As I say, the numbers are hypothetical - because it is the numbers I am seeking here!!

 

[Agile]

I am sorry but all of that is just because you apparently cannot understand that the amount of heat provided is totally proportional to the amount of time that you have heating on.

Its so simple but about 30% of people still cannot understand it.

Unfortunately perhaps 15% of heating engineers don't either!

Tony

 

[reg091]

Thanks Tony, but again I wonder if we are confusing definitions. I am not interested in the amount of heat provided. I am interested in the most efficient way of maintaining that heat: heating in short regular bursts, or longer less regular bursts. Sorry, but that seems quite a simple difference of gas consumption over a set period.

Maybe there is no difference in consumption, or no one has ever bothered to work it out?

 

[EFLImpudence]

Surely it is impossible to say without, as has been said, knowing the efficiency of your insulation, i.e. heat loss.

Obviously if you go out and leave all the doors open it will be better to switch off the heating until you come home and shut the doors.

Conversely if your insulation were 100% efficient, i.e. no heat loss, it won't matter whether you leave the heating on or turn it off.

 

[kbdiy]

A couple of years ago my daughter and granddaughter (a young baby) stayed with us over the winter period - November to January. As she was a newborn we ran our heating 24/7. Bearing in mind we have good loft insulation (over 400mm) and full fill cavity insulation, our bills were somewhat higher than we would normally have expected, leading me to conclude that it isn't more efficient to run 24/7. I didn't do the maths but the results were fairly obvious.

But it was lovely and warm all the time

 

[Galoka]

Surely it is impossible to say without, as has been said, knowing the efficiency of your insulation, i.e. heat loss.

Obviously if you go out and leave all the doors open it will be better to switch off the heating until you come home and shut the doors.

Conversely if your insulation were 100% efficient, i.e. no heat loss, it won't matter whether you leave the heating on or turn it off.

Not really, it doesn't change the principle of the situation.

A well insulated building will lose less heat, but it will still be cheaper to only heat it when required.

What will be different is the is the benefit in terms of energy used and money saved.

 

[Galoka]

Thanks Tony, but again I wonder if we are confusing definitions. I am not interested in the amount of heat provided. I am interested in the most efficient way of maintaining that heat: heating in short regular bursts, or longer less regular bursts. Sorry, but that seems quite a simple difference of gas consumption over a set period.

Maybe there is no difference in consumption, or no one has ever bothered to work it out?

Would you leave your heating on full if you were away for two weeks in winter - probably not, the same principle applies for a day.

Of course there is a difference. Leave your heating on and measure the consumption, then do the same with the heating turned off when un-needed.

As to calculations - Gas consumption and heat provided/lost are pretty much directly related, added to which a greater temp differential leads to a greater heat loss. So the warmer the house is the more heat it will lose in proportion. So more heat and more gas will be required.

There is another aspect though which gets mixed up in this, and that is one of comfort. And it can certainly then be worth keeping heating on at a reduced temp. e.g We've an old victorian house, solid walls, big thermal mass, still kinda drafty, lots of single glazed windows etc.

If the house gets too cold it takes ages to heat up ( you can notice especially if we have a really cold spell early in winter before we have had the heating on much to warm up the fabric of the house) so we used a programmable stat to ensure the temp doesn't drop to low.

 

[Onetap]

Thanks Tony, but again I wonder if we are confusing definitions. I am not interested in the amount of heat provided. I am interested in the most efficient way of maintaining that heat: heating in short regular bursts, or longer less regular bursts. Sorry, but that seems quite a simple difference of gas consumption over a set period.

Maybe there is no difference in consumption, or no one has ever bothered to work it out?

It has been worked out.
The most efficient heating method is to;

1) heat the building (and/or zones) only during the occupied periods

and 2) provide the heat with a modulating condensing boiler with a variable flow temperature, so that the standing losses are minimized by keeping the flow temperature to the minimum required for the heat emitters to supply the necessary heat output.

The theory is quite simple, the only adherents of the 24/7 argument are those who are unimpeded by any understanding of the simple theory.

If you turn the heat off, the internal temperature will drop gradually, as will the heat losses.

The only circumstances under which continous heating would be required (apart from frost protection) are in building with a very high thermal mass or heating systems with a big time lag (UFH in screeded concrete). It rarely applies to houses.

 

[D_Hailsham]

Would you leave your heating on full if you were away for two weeks in winter?

When we all went away for two weeks at the end of September, I set the prog stat in 'holiday' mode with a temperature of 10C and took a meter reading. On return I took another reading, then calculated the gas used over the fortnight: it was 31kWh. But that included they day we returned, when the heating automatically reverted to the required 21C so it was warm. My consumption at that time of the year is about 25kWh per day, which leaves about 6kWh used over the two weeks to keep the temperature at 10C.

 

[ALEC1]

This highlights the importance of set back temperatures...its important that things don't get too cold that require a lot of heat very quickly...

If a house has people up and about 16 hours out of 24 hours then it probably is cheaper to keep the heating running (but only with ca boiler which can vary flow temperature according to demand)

On the other hand heating a rarely used village hall 24/7 would be a waste of money...

clearly efficient use of energy is related to occupancy rates and usage... a fact oft missed out by people...

 

[JohnD]

there is no point, but considerable expense, in keeping a building heated to comfort levels when there is no-one there to appreciate the comfort; or when the occupants are warmly tucked up in bed.

the warm-up and cool-down periods can be accommodated using the timer.