What's the cheapest way to run my heating?

fwor

Incidentally this has been covered on this forum many times before. In one of those threads from 2009, Cardew provided this quote from the Energy Saving Trust:

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.

Ok, that was a couple of years ago, but I doubt that the laws of physics have changed since then.

robatwork

I can't cite the research but I know I read this somewhere.

Unless you live in a fantastically cold place it isn't economic to leave the heating on low - just let it come on an hour-ish before you come home.

Of course if it's -30 here for a few weeks in winter then you won't want to let your pipes inside freeze....otherwise keep the heating off for as long as possible

Avoriaz

keithgillyon wrote: »

No I don't agree, providing your house has a certain amount of insulation then 1) it is far better to leave the heating on low ie 12-15, if you let the fabric of the building cool down too much then not only will it take longer to heat the rooms but it will cost more, you shouldn't keep moving your stat around it should be in the room that doesn't have a trv (normally the hall) the trv's are fitted to do a job ie control the heat from the rad they are fitted to & they can't do that if your stat is constantly turning off the heating, fit the stat to the wall & leave it there & use the trv's to control the temp in the individual rooms that's what they are there for.

Take the pan thing, if the water is already warm/hot how long & how much less gas does it take to boil ? much less than if the water was cold, 2) a cold house will take hrs to heat up so by the time you get in from work & you have finally got it to where you want it then it's time for bed, so as you may have gathered my advice is to leave it on low.

1) That defies the laws of physics. Keeping a house at 15 degrees when you are out is more expensive than letting to cool down.

Imagine how much fuel you would use if you left the house for a year with the heating on at 15 degrees so that it was quicker to warm up when you returned from a round the world trip.

2) That is easily solved with a timer that is set to start warming the house before you get home.

ian103

we had always used the heating on a timer, not in heating off etc, then we moved into an older property built with a cavity wall of engineering style brick outer skin and common brick inner skin, tried this on a timer run option and boy it always felt cold except at weekend when we had the heating on more, we then had a new thermostat fitted with 2 settings (we used 14 degC and 20 deg C, heating always on but 14deg C unless we were sitting down / relaxing then at 20deg C. house always felt better, it was warmer, it heated up at night much quicker, we never boosted the heating in the morning as it was warm enough for us, AND more importantly our gas bill was less and even more importantly OH never moaned that she was cold! so from a very unscientific test we now always have our heating on albeit at 15deg C generally and turned up later.

southcoastrgi

Avoriaz wrote: »

1)Imagine how much fuel you would use if you left the house for a year with the heating on at 15 degrees so that it was quicker to warm up when you returned from a round the world trip.

OMG you really don't want me to answer that completely stupid statement, do you ?

ian103 wrote: »

we had always used the heating on a timer, not in heating off etc, then we moved into an older property built with a cavity wall of engineering style brick outer skin and common brick inner skin, tried this on a timer run option and boy it always felt cold except at weekend when we had the heating on more, we then had a new thermostat fitted with 2 settings (we used 14 degC and 20 deg C, heating always on but 14deg C unless we were sitting down / relaxing then at 20deg C. house always felt better, it was warmer, it heated up at night much quicker, we never boosted the heating in the morning as it was warm enough for us, AND more importantly our gas bill was less and even more importantly OH never moaned that she was cold! so from a very unscientific test we now always have our heating on albeit at 15deg C generally and turned up later.

thank you Ian

Leif

Avoriaz wrote: »

1) That defies the laws of physics. Keeping a house at 15 degrees when you are out is more expensive than letting to cool down.

Imagine how much fuel you would use if you left the house for a year with the heating on at 15 degrees so that it was quicker to warm up when you returned from a round the world trip.

2) That is easily solved with a timer that is set to start warming the house before you get home.

1) Yes, I agree.

You can consider the house as no more than a lump of brick, with a large internal cavity, and a means to heat the air inside. Assume a constant outside temperature (not true, but easier to think about), then keep the heating on so that the air inside is at a constant temperature. There will be a constant 'leak' of heat energy from the inside, to the outside. Now turn off the heating for 6 hours. If we assume the heat leak remains constant, then the energy required to get the inside back up to temperature again after 6 hours is the same as the energy we would have expended keeping the inside at a constant temperature for 6 hours. We are just replacing the heat lost! Simples. But ... and it is a big but ... the heat loss is not constant if the house is cooling. In fact the cooler the house gets, the slower the heat loss, as the thermal gradient is less. It's rather like a water butt full of water. Turn on the tap and the water rushes out. But as the mass of water in the butt gets less, so the pressure gets less, and the rate of flow from the tap reduces. If you don't believe me, think about a house that is 1,000 Celcius inside. Would the heat loss be the same for a house at 21 Celcius inside? Of course not. Anyone near the first house would be well and truly fried as it would be losing huge amounts of heat. Yes this is an extremely silly example, unlikely to be encountered with current boilers, but I am using it to demonstrate the principle that the rate of heat loss from the house increases as the internal temperature increases.

How much you save by turning off the heating during the day depends on how rapidly the house cools. Some houses are so well insulated they barely need heating, and in this case you might as well leave the heating on, but I am talking about energy saving houses, with triple glazing and silly amounts of insulation, not your typical house.

Oh, and the above does not take into account boiler efficiency. I think someone said the boiler is more efficient at high power, so that would add to the argument "best turn off during the day", as rather than chugging along at low power during the day, it would have a high power blast at 4pm say, to warn the house up ready for you to return home.

Interesting question, and I'm glad it was asked as I've never thought about the processes at work before. I'll keep the heating off during the day, except in freezing conditions where I will keep it low.

Leif

keithgillyon wrote: »

OMG you really don't want me to answer that completely stupid statement, do you ?



thank you Ian

I think Ian was making a different point, namely that in his case the house was not so well insulated, so it was quite hard to get it back up to temperature after letting it cool during the day. As to why he says it was cheaper, he did say the test as unscientific, so without knowing the weather conditions before and after it is impossible to comment.

southcoastrgi

Leif wrote: »

I think Ian was making a different point, namely that in his case the house was not so well insulated, so it was quite hard to get it back up to temperature after letting it cool during the day. As to why he says it was cheaper, he did say the test as unscientific, so without knowing the weather conditions before and after it is impossible to comment.

i fail to see how ian was making a different point, he answered the OP with his experience, i think what he was ref to as unscientific was that he didn't know heat losses etc but did know how much he saved in his wallet which after all was what the OP asked in the first place.

Leif

keithgillyon wrote: »

i fail to see how ian was making a different point, he answered the OP with his experience, i think what he was ref to as unscientific was that he didn't know heat losses etc but did know how much he saved in his wallet which after all was what the OP asked in the first place.

It was unscientific because it was not controlled. The two cases he talked about had too many different variables to be conclusive. As I indicated, we know nothing about the weather conditions (outside temperatures, day and night) in the two cases. And that is crucial.

Ian explained that the reason he decided to turn the heating on during the day was because the house felt too cold. So in his case having the heating off in the day was a bad idea. It sounds like it got too cold, and the heating struggled to warm the house up again. He also mentioned he saved money, but as I said, there are too many variables here to know why.

But at the end of the day the laws of thermodynamics always apply. They are fundamental and not optional.

southcoastrgi

still at least the woman's beach volleyball is warming me up