Energy myth-busting: Is it cheaper to have heating on all day?

BikingBud

Petriix said:

No, it doesn't depend... More heat = more heat loss. It's objective fact. There are many variables which can make it more difficult for people to observe the basic physics at play, but the fundamental principle is unquestionable.

Yes it depends upon the case in question which is entirely driven by the 7 or so variables. But most people on here don't want to or cannot understand the basic physics! For instance your comment more heat means nothing! 

Greater heat difference (dt) however does mean something. Energy levels will try to equalise and you either want to sustain a higher temp inside relative to outside, (+ve dt) heating, or sustain lower temp relative to outside, (-ve dt) air con.

All systems have observables and controllables. Older heating systems are very limited in what you can observe and control eg, higher or lower room temp, hotter water or cooler water. Interestingly energy consumption is not often observed and yet this is the real measure you are after tracking as this is your cost.

You can add discrete sensors to observe more state conditions but if you wish to control the system via those observations they need to be applied in a methodical manner to remove and correct the effect of other variables or invest in a more complex system such as external temp compensation.

Most people do not look at their poorly designed system critically and do not invest in understanding the difference between their own system and how it operates and how a well designed scientific test of a modern condensing boiler with defined and repeatable parameters to provide empirical evidence to support the result may offer an accurate result.

Comparing one day where the heating was left on or the temps were adjusted to the next where they turned it off misses so many potential variables and as the well-presented answer from heat geek advises you need to understand your system and what benefits you want and how much you are willing to pay for it, (the usage case).

I have lived in a four storey house with wet UFH, high thermal mass, all concrete, that took 3 days to heat up, with winter temps touching -20 deg C fairly common. To ensure it was running most efficiently it had external temp compensation and night set back, this was 20 years ago!

Hence my comment about it depends and everybody being correct and incorrect.

Simple answer and only one which fits all test cases, most efficient = turn heating off!

But we want the comfort of heating homes and that as with most of this discussion is subjective.

Ultrasonic

richardc1983 said:

But the point many of us are trying to make is less heat such as 18/19c 24 hours a day with say as low as 30c flow temp (low and slow because the house fabric is already maintained) is potentially less heat loss than 22/23c 8 hours a day and off in between with 70/80c flow temp. The higher comfort temp and flow temp is what is using more gas POTENTIALLY. 

That's a false choice. Why not 18/19°C 8 hours per day instead? That's much closer to what I do.

BikingBud

Ultrasonic said:

Most people seem to want a cheap heating system that just kind of works, they do not invest in the system that would give best control and efficiency, they do not invest in understanding how to optimise the system if at all possible. Focus on and demand for energy efficient systems is currently extremely low but people seem quite happy spending loads on a shiny new kitchen  

Most people probably replace a kitchen when it needs doing, and do the same with a boiler. It also probably doesn't make financial sense for most to replace all but the oldest/most inefficient of boilers.

Replacing a boiler is also not an option for the huge number of people who rent their homes.

Yet some replace kitchen because they don't like the colour of the doors or "want" a granite worktop, not when it needs doing.

Whereas installing a newer more controllable and more efficient boiler, rather than throwing in an £800 monstrosity, would be an investment. However, people were not previously bothered as energy costs were quite low and were therefore not engaging or understanding. 

Perhaps the revised EPC obligation on landlords may lead to more efficient systems being installed.

Cardew

BikingBud said:

However, people were not previously bothered as energy costs were quite low and were therefore not 'engaging or understanding.'

Perhaps the revised EPC obligation on landlords may lead to more efficient systems being installed.

However first they need to revise the standards of the EPC 'inspectors' to get them engaging or understanding.  Many appear to be 'housepersons'(gender neutral!) who do the job for pin money and work to a rigid inflexible template. A cup of tea and flattery can get you a higher rating.

I suspect a model xxxx boiler will get a tick in the appropriate box regardless.

BikingBud

Ultrasonic said:

richardc1983 said:

But the point many of us are trying to make is less heat such as 18/19c 24 hours a day with say as low as 30c flow temp (low and slow because the house fabric is already maintained) is potentially less heat loss than 22/23c 8 hours a day and off in between with 70/80c flow temp. The higher comfort temp and flow temp is what is using more gas POTENTIALLY. 

That's a false choice. Why not 18/19°C 8 hours per day instead? That's much closer to what I do.

That's not a false choice that's just different to your usage case, that you want to apply to meet your required comfort levels.

Some on here are quite happy at ~15/16 deg is that also a false choice?

The point I'm trying to make is that most systems/installs will be different, most needs will be different, most levels of insulation will be different, as people have mentioned on here tolerability to system noise will be different.

You could set most parameters the same eg wet UFH, condensing boiler able to moderate down to 30 deg, manifold temp 40 deg, harsh winter with external temp compensation, heavy concrete structure leading to significant high thermal mass/ system lag where anything other than being on all the time would unlikely deliver the required level of comfort.

Retain all other factors but switch the building for a low thermal mass with radiators where you are heating air rather than building fabric and the response times maybe quicker then frequent cycling may be the answer or may not be depending upon the emitter panel temp which means you cannot operate in the most efficient condensing range of the boiler that other systems can.

I have an old boiler, so old I cannot get a manual or an indication of how (in)efficient it is. I am reviewing options and seeking systems that will operate towards 98% efficiency, that will operate with most foreseeable gas blends, that provide remote operation, system set back, weather compensation etc. I expect the supplier/system designer to be able to explain what system suits my usage case best and how to operate it most efficiently, if that is not forthcoming then a different supplier may be the answer, or changing my expectations may be.

We have to pay for the comfort, as a through life not just ongoing cost, but understand your own system and learn how to optimise it to sustain your desired levels of comfort as the real issue is addressing needless wasted energy.

Ultrasonic

BikingBud said:

Ultrasonic said:

richardc1983 said:

But the point many of us are trying to make is less heat such as 18/19c 24 hours a day with say as low as 30c flow temp (low and slow because the house fabric is already maintained) is potentially less heat loss than 22/23c 8 hours a day and off in between with 70/80c flow temp. The higher comfort temp and flow temp is what is using more gas POTENTIALLY. 

That's a false choice. Why not 18/19°C 8 hours per day instead? That's much closer to what I do.

That's not a false choice that's just different to your usage case, that you want to apply to meet your required comfort levels.

Some on here are quite happy at ~15/16 deg is that also a false choice?

Errr, you appear to have missed that I responded to something very specific, and not written by you. What I quoted was a false choice.

richardc1983

Ultrasonic said:

richardc1983 said:

But the point many of us are trying to make is less heat such as 18/19c 24 hours a day with say as low as 30c flow temp (low and slow because the house fabric is already maintained) is potentially less heat loss than 22/23c 8 hours a day and off in between with 70/80c flow temp. The higher comfort temp and flow temp is what is using more gas POTENTIALLY. 

That's a false choice. Why not 18/19°C 8 hours per day instead? That's much closer to what I do.

No it's not a false choice. That is my choice and it IS cheaper for us this way. It is cheaper than us overheating the air temperature of the house to 22/23c at timed periods so the fabric and contents of the house did not feel as cold as these lagged behind and were the slowest to come up to a comfortable temperature etc. Why would I go any lower when I am happy at 18/19c constantly. 

Astria

Petriix said:

No, it doesn't depend... More heat = more heat loss. It's objective fact. There are many variables which can make it more difficult for people to observe the basic physics at play, but the fundamental principle is unquestionable.

I agree, to a point. My heating is on thermostat 24/7, I never turn it off with a timer. If I'm on holiday for a few days I will set the thermostat to something sensible like 12c for 24/7 operation. When I'm a few hours away I'll shall turn it up to about 18c.

If I'm going out for a few hours to have a meal and a movie (for example) then I won't bother to turn it off as, for me at least, there are no savings by doing so.

Petriix

BikingBud said:

Petriix said:

No, it doesn't depend... More heat = more heat loss. It's objective fact. There are many variables which can make it more difficult for people to observe the basic physics at play, but the fundamental principle is unquestionable.

Yes it depends upon the case in question which is entirely driven by the 7 or so variables. But most people on here don't want to or cannot understand the basic physics! For instance your comment more heat means nothing! 

Greater heat difference (dt) however does mean something. Energy levels will try to equalise and you either want to sustain a higher temp inside relative to outside, (+ve dt) heating, or sustain lower temp relative to outside, (-ve dt) air con.

All systems have observables and controllables. Older heating systems are very limited in what you can observe and control eg, higher or lower room temp, hotter water or cooler water. Interestingly energy consumption is not often observed and yet this is the real measure you are after tracking as this is your cost.

You can add discrete sensors to observe more state conditions but if you wish to control the system via those observations they need to be applied in a methodical manner to remove and correct the effect of other variables or invest in a more complex system such as external temp compensation.

Most people do not look at their poorly designed system critically and do not invest in understanding the difference between their own system and how it operates and how a well designed scientific test of a modern condensing boiler with defined and repeatable parameters to provide empirical evidence to support the result may offer an accurate result.

Comparing one day where the heating was left on or the temps were adjusted to the next where they turned it off misses so many potential variables and as the well-presented answer from heat geek advises you need to understand your system and what benefits you want and how much you are willing to pay for it, (the usage case).

I have lived in a four storey house with wet UFH, high thermal mass, all concrete, that took 3 days to heat up, with winter temps touching -20 deg C fairly common. To ensure it was running most efficiently it had external temp compensation and night set back, this was 20 years ago!

Hence my comment about it depends and everybody being correct and incorrect.

Simple answer and only one which fits all test cases, most efficient = turn heating off!

But we want the comfort of heating homes and that as with most of this discussion is subjective.

You've used a lot of words to say very little, and especially little about the actual question.

Unless you're talking about using an expensive form of immediate heating to make up for your cheaper heating method which you've switched off, the end result is fairly simple...

The less time your heating is on for (at the same thermostat temperature) the less energy you will use. There are no circumstances under which leaving the heating on all day while you're out will use less energy than leaving it off all day; as long as you are otherwise using the same settings while you're home. 

Ultrasonic

richardc1983 said:

Ultrasonic said:

richardc1983 said:

But the point many of us are trying to make is less heat such as 18/19c 24 hours a day with say as low as 30c flow temp (low and slow because the house fabric is already maintained) is potentially less heat loss than 22/23c 8 hours a day and off in between with 70/80c flow temp. The higher comfort temp and flow temp is what is using more gas POTENTIALLY. 

That's a false choice. Why not 18/19°C 8 hours per day instead? That's much closer to what I do.

No it's not a false choice. That is my choice and it IS cheaper for us this way. It is cheaper than us overheating the air temperature of the house to 22/23c at timed periods so the fabric and contents of the house did not feel as cold as these lagged behind and were the slowest to come up to a comfortable temperature etc. Why would I go any lower when I am happy at 18/19c constantly. 

To me the only meaningful comparison is the same temperature achieved by two different approaches, not different temperatures by different methods.