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

docnarrative

macman wrote: »

Complete nonsense-since all electric heaters of whatever kind have the same efficiency (100%), they all cost excactly the same to run, for the same rated output. So just buy the cheapest.
The only difference between the two is the method of delivery. An oil-filled rad is slower to produce full output, but retains some residual heat after switch-off. But the cost per kWh is the same.

Thanks for the advice – much appreciated!

bwg

I've read all the threads for this and all I can say is, try keeping your heating on all day and see how it affects your bills. For years I have been reading about people who make a judgement without any hard evidence.

I first heard of this system in the mid 1970s and, being a Yorkshireman by birth and an accountant by training, I thought it was a load of tosh. Fortunately I decided to give it a try.

I decided to read the meters (both gas and electric) when I came home from work each Friday evening. I ran the heating week about with one week on my previous regime of 3 hours in the morning and 4 hours in the evening and the following week leaving it on constantly.

From the start, I was surprised at the small difference in gas consumption so decided to continue monitoring it throughout the whole of the winter. After a month my wife remarked about how much warmer the house was in the latter half of the constant heat week. The difference in the consumption of gas was negligible but the consumption of electricity was markedly different. When the heating was on the twice daily cycle our consumption of electricity soared (when the heating went off my wife and newborn son hibernated to the lounge in their winter clothes and sat shivering around our electric fire all day). After 6 months monitoring I was totally sold on the benefits, so have been running our heating on this system ever since. Please try it before you discount it.

A couple of additional points. First, if you have your heating on twice a day do you find it difficult to keep your feet warm? Of course you do! The heat that you pump out to get the room warm rises to the ceiling, cools, comes down as cold air to the floor cooling your feet as it passes until it reaches the radiator; it then heats up again and repeats the process. Your feet don't get warm until the radiator has heated all the walls and cut down the convection cooling effect. Take it from my experience, walls of a standard construction can take up to 2 days of constant heating to warm them up (a couple of years ago I turned the heating down to frost protection during a February break in the Canary Isles and my wife has never let me forget how cold the house was when we returned home). Internally insulated walls do heat up quicker. Secondly, I should perhaps mention that this is not an isolated experience in one house. I was in the RAF for 30 years and lived in 14 different houses over that period. In most of these houses I did the same monitoring to make sure that the system worked in our new house. In none of the houses did I find that the gas consumption was excessive but the comfort of the constant heating was markedly superior to that of neighbours who ran their heating on the standard twice daily cycle.

Like rgn007 we leave our heating on all the year round. However, a word of caution, you may find that you need to make sure your bedroom doors are kept closed and the thermostatic valves turned down otherwise you might roast in bed. My wife, being akin to an iceberg declines to do so. We therefore use 3.5 tog duvets all year round!!

Yanbanshee

It is interesting to read the article relating to comparisons between timers and thermostats. One thing our energy savers seem to forget is that there is an optimum temperature at the radiator in order to enable effective radiation. Something in the order of 180f is necessary for max efficiency. So turning down the boiler circulation temperature WILL ACTUALLY COST YOU MONEY. The same can be said for having the timer cut off the heating for certain periods. During the heating up phase the efficiency is below max efficiency, so there is no easy answer to the debate re "all day verses on off" Keep everything to max efficiency far maximum savings. This debate also follows regarding comparing tarrif costs. Certainly a unit of gas based BTU is cheaper than an electricity based BTU. However electric heaters are 100% efficient, whereas the best gas/water heaters are only around 80% efficient. Actually if we had a proper energy policy in this country we would all be using electric central heating.:xmassmile

Craig_Lawrance

With a modern well insulated house AND underfloor heating I would recommend leaving the heating on overnight at say 17 degrees and then having it ONE degree higher during the day.

This is because the insulation helps retain the heat overnight, and raising the temperature by just one degree does not require that much energy. Conversely asking underfloor heating to raise the temperature by 2 or 3 degrees during the day WILL demand a lot of energy.

However, if you have more traditional radiator heating, I absolutely would not recommend this approach. Instead heat it only when you need it.

If you have a water tank that you heat for showering etc, again it takes a lot of energy to heat it from the ambient winter temperature up to a more comfortable one for showering and baths. Depending on how often you require hot water, it's often more fuel efficient to keep the water at an intermediate temperature even when you don't need it. This is somewhat akin to driving a car from 30 to 60 or from 0 to 60 - which takes more energy? During summer when the ambient temperature is say 20 degrees, heating the water to 40 degrees for showering is only a 20 degree difference - in winter the difference between zero and 40 is double that.

gledhillme

Apologies if this has already been mentioned, i didnt have the time to read all 13 pages of comments,

of course all things being equal you should only put the heating on when you need it as common sense and physics mean that heat will be wasted when the house is empty.

But are all things equal? that assumes that the boilers run with the same efficiency at all temperatures?

I think that modern condensing boilers work more efficiently when the return temperature is below 56 degrees C. (so they can condense...) Im not sure how much difference this makes but at least in theory it may use less energy if the heating is on for a longer time at low temperature rather than for a shorter time flat out.

whether its worth leaving on all the time, dunno, depends on how long you are out for and how good the insulation is, but its a good idea to not have the boiler temperature on full if you can help it and if this means say having it come on lower an hour or two before you get back that may help.

of course this only applies to condensing boilers not sure if there is any efficiency differences with other boiler types.

Im not a heating engineer, if there are any out there would be interested in your comments on this.

dg

tgroom57

I have 2 snippets to add: (not having read all 13 pages)

Economy 7 - timed tariffs If you have a timer as well as a meter you might like to check the cheap rate supply turns on and off at the times you have been led to believe. It would come as a nasty shock to find otherwise. I check every other month.

Airers indoors: if you have a choice, put your airer at the top of the house - over the bath is good, but in any case, upstairs. Heat rises to your top floor, it doesn't stick around in the kitchen.

macman

bwg wrote: »

I've read all the threads for this and all I can say is, try keeping your heating on all day and see how it affects your bills. For years I have been reading about people who make a judgement without any hard evidence.

I first heard of this system in the mid 1970s and, being a Yorkshireman by birth and an accountant by training, I thought it was a load of tosh. Fortunately I decided to give it a try.

I decided to read the meters (both gas and electric) when I came home from work each Friday evening. I ran the heating week about with one week on my previous regime of 3 hours in the morning and 4 hours in the evening and the following week leaving it on constantly.

From the start, I was surprised at the small difference in gas consumption so decided to continue monitoring it throughout the whole of the winter. After a month my wife remarked about how much warmer the house was in the latter half of the constant heat week. The difference in the consumption of gas was negligible but the consumption of electricity was markedly different. When the heating was on the twice daily cycle our consumption of electricity soared (when the heating went off my wife and newborn son hibernated to the lounge in their winter clothes and sat shivering around our electric fire all day). After 6 months monitoring I was totally sold on the benefits, so have been running our heating on this system ever since. Please try it before you discount it.

A couple of additional points. First, if you have your heating on twice a day do you find it difficult to keep your feet warm? Of course you do! The heat that you pump out to get the room warm rises to the ceiling, cools, comes down as cold air to the floor cooling your feet as it passes until it reaches the radiator; it then heats up again and repeats the process. Your feet don't get warm until the radiator has heated all the walls and cut down the convection cooling effect. Take it from my experience, walls of a standard construction can take up to 2 days of constant heating to warm them up (a couple of years ago I turned the heating down to frost protection during a February break in the Canary Isles and my wife has never let me forget how cold the house was when we returned home). Internally insulated walls do heat up quicker. Secondly, I should perhaps mention that this is not an isolated experience in one house. I was in the RAF for 30 years and lived in 14 different houses over that period. In most of these houses I did the same monitoring to make sure that the system worked in our new house. In none of the houses did I find that the gas consumption was excessive but the comfort of the constant heating was markedly superior to that of neighbours who ran their heating on the standard twice daily cycle.

Like rgn007 we leave our heating on all the year round. However, a word of caution, you may find that you need to make sure your bedroom doors are kept closed and the thermostatic valves turned down otherwise you might roast in bed. My wife, being akin to an iceberg declines to do so. We therefore use 3.5 tog duvets all year round!!

Like so many proponents of this fantasy, you are confusing cost with comfort. Leaving the heating on 24/7 is of course more comfortable, but it is not certainly cheaper, and never could be, even if your house had no thermal loss whatsoever.
Two completely different arguments.
Yout test was entirely unscientific, as it failed to take into account the differing ambient temps from day to day and week to week.

HappyMJ

Craig_Lawrance wrote: »

With a modern well insulated house AND underfloor heating I would recommend leaving the heating on overnight at say 17 degrees and then having it ONE degree higher during the day.

This is because the insulation helps retain the heat overnight, and raising the temperature by just one degree does not require that much energy. Conversely asking underfloor heating to raise the temperature by 2 or 3 degrees during the day WILL demand a lot of energy.

However, if you have more traditional radiator heating, I absolutely would not recommend this approach. Instead heat it only when you need it.

If you have a water tank that you heat for showering etc, again it takes a lot of energy to heat it from the ambient winter temperature up to a more comfortable one for showering and baths. Depending on how often you require hot water, it's often more fuel efficient to keep the water at an intermediate temperature even when you don't need it. This is somewhat akin to driving a car from 30 to 60 or from 0 to 60 - which takes more energy? During summer when the ambient temperature is say 20 degrees, heating the water to 40 degrees for showering is only a 20 degree difference - in winter the difference between zero and 40 is double that.

It takes more energy driving a car along at 30 then accelerating to 60 as opposed to having a car turned off at a standstill at 0 then accelerating to 60.

I don't like that analogy anyway as a car does not compare to heating...Do you keep your car's engine running and the heating system running overnight so it is warm and comfortable for you in the morning when you get in the car and the windows are nicely defrosted for you or is having the car running all night more expensive than turning it off and letting the windows freeze?

Do you when you leave a property for a 2 week summer holiday leave the boiler turned on and keeping the hot water cylinder hot so that you have hot water when you come back off holiday and do you still say that is cheaper than turning it off letting it cool to ambient temperature and turning it on when you get back and waiting an hour for hot water?

wantanswers

victor2 wrote: »

It's that time of year again....:)
Just out of curiosity, I did a simple test the other day.
I let the house cool down from the central heating being on with the thermostat set at 19 degrees C. After 6 hours the thermostat said it was 16. The outside temperature was indicated as 4 on my cheapo digital thermometer.
I switched the heating on and monitored the gas usage (an old inefficient boiler by modern standards). It took 3 hours and 39.9kWh of gas to get the thermostat back up to 19. By which time the outside temp had dropped to 1.
From that point on, the boiler was using 9.2kWh of gas per hour.
So, if I'd left the boiler on for the 9 hours, I would have used just over 82kWh of gas, probably a bit less as the outside temperature was mostly a bit higher than when it finished. About twice as much gas over 9 hours compared to switching the boiler off for 6 hours then heating the "cold" house up.

Not a huge expense to leave the heating on, and certainly more comfortable, but an extra cost nevertheless. Which as already said, if it's on, it's costing money, if it's off, it isn't.

Hi there Victor 2, any joy re a comparison yet after the figures I gave on my test a few posts ago? I'm just interested.

From what you have said it appears you use about 33% more gas than me although I do accept we may have different 'variables' in there somewhere. Cheers!

malc_b

My 2p.

I was going to post on the airing wet clothes in the house but I see someone has already posted on that - namely the most efficient method is to use a clothes line in summer and in winter consider using a condensing tumble dryer. I'm oil and also have E7. E7 night rate is just cheaper than oil so if I use my condensing tumbler dryer in the winter not only do I dry the clothes without adding damp to the house (which will thus require me to increase ventilation and so require more heat) but the heat from the tumble dryer heats the house cheaper than my oil.

On the subject on heating on 24/7 or not I would suggest a PID thermostat. I have a CM67. With these you set what temperature you want and when and it works out when to turn the heating to reach that. I've also the notes from a uni course on this subject which I found on the net somewhere a while ago. The file is called 10-Energy_consumption.pdf. In that are factors to apply when heating buildings, 7 day week is a factor of 1. 5 day week is 0.75-0.85 depending on light or heavy structure (5/7 = 0.71). This show that you need some energy to heat the structure. You see similar factors for day, 24hrs is 1, a night shutdown is 0.55-0.70 for a light structure and 0.85-0.95 for heavy structure. So again you don't save that much with a night shutdown. What also needs to be factored in is that a cold house feels cold which may result in the thermostat being set higher, and boilers are often not very efficiency when running flat out, they tend to cut in and out with the water at max temp and that hurts efficiency. All which could very well give lower consumption. However the solution is better controls which can raise the temperature steadily.

For those who like physics we can do a thought experiment. Consider a one room house, inside 20C, outside 0C, losses 1kW. Heat it 24hrs at a constant 20C and it takes 24kWh. So what happens if we turn off the heating 11pm to 7am. What are the house losses at 11:01pm? 1kW since the inside temperature is still 20C. If we assume the house reaches 10C (brrr!) by 7am and take as linear (which is isn't) then average temp overnight is 15C so losses are 1000x15/20 = 750. We have saved 0.25*8 = 2kWh out of 24kWh or 8.3%. During the night we have used 6kW rather than 8kWh which has come out of the fabric of the house. In the morning we have to put that 6kW back as well as providing the 750W-1kW to balancing the losses. If our heater was 2kW then it would take ~6hrs to put back that loss during which time the house feels colder than we'd like. And a factor of 2 over design on system is not unrealistic. Most probably don't have that. Boilers might be x 2 but radiators are usually not that much over.

And for those that have read to the end of this long post - congrats :j