Heating efficiency question

[kzb]

Pretty cold (for us) in England currently, and I have been having an argument about heating costs.

Some people say that it works out cheaper to leave the central heating on all the time. Or alternatively, set the timer so that it goes on-off-on-off in a 15 minute cycle.

Now this seems bizarre to me, but the thing is I have heard it several times over the years from different people.

Also when I was at school (longer ago than I care to mention), our physics teacher, no less, stated that you should leave your hot water immersion heater on constantly, again because it used less juice that way.

I can't see how these ideas can be true, but nevertheless they seem to have widespread support in the population. So the questions are

Are these things true?

If so, exactly why?

If NOT true, how did these ideas gain support in the population?

Thanks

[Neverfly]

Mostly, it is true.

You see, it takes less energy to heat a warm house than a cold house.

Think of sitting in your car at a traffic light. Then the light turns green, you put the car in first gear and pull out. Then you shift to second, third , forth...

This consumes a lot more fuel- coming from a dead stop, than if the car was already in motion.

That's why you have kpg(mpg)/highway and kpg(mpg)/city. On the highway you can get 40 mpg but in the city you get 12 mpg.

[BioSci]

Nope, it takes the least total energy to warm a house only when needed - a hot house looses more heat than a cool house.

That is why it is recommended to "turn down" thermostats at night and during the day if house is not occupied or if one goes on vacation!

[Ivan Viehoff]

Sorry Neverfly, that doesn't add up. Obviously it takes less energy to heat a warm house than a cold house. Indeed, if the house is already warm enough, we don't need any energy at all. But the warm house had to be made warm in the first place, and what actually is at issue is how much energy we need to keep it warm, ie, to counteract heat losses.

Obviously, letting the house cool and then heating it up again uses less energy than keeping it warm continuously, because there are lower energy losses - there is simply less energy there to be lost when the house is cooler, and it loses energy at a lower rate when the temperature difference is smaller. So we need less energy from the heater if we periodically let the house cool down. We can leave the house cold for ever and not use any energy at all. But that isn't a very interesting result, and I suspect has nothing to do with the question.

In practice, we are not interested in the situation in which the temperature of the house has such large fluctuations that the heat losses change materially. We are interested in keeping the house close to the desirable warmth during the time we occupy it. In general the output of the heat source will be different from the heat losses we are counteracting. So we have to run the heater intermittently, and typically allow the temperature to fluctuate over a narrow range. I suspect therefore the true issue is whether we should run the heater at a high output for short bursts, or whether we should run the heater at a lower output for longer bursts, and thus with fewer on/offs: in the perfect case, when the heater output precisely matches the heat losses, the heater can be run continuously. But unless the heater has its output continuously adjusted, which doesn't happen in practice, we can't achieve the perfect situation.

I suspect this is to do with the efficiency of start-up of boilers. Probably central heating boilers run a lot less efficiently at start-up, as it has to warm up to an efficient operating temperature. So perhaps it is more efficient to set the boiler to a lower output and run it with fewer ons and offs, ideally more or less continuously (for the period when you need heating). But you would need to check that your boiler didn't run less efficiently at lower output than at higher output, which might well be the case. So there might be a compromise, not run the boiler at too low an output that it produces inefficiently, or such a high output that it is turning on and off all the time.

The above has then been mis-applied to different situations. In the specific case of an immersion heater for hot water, I cannot imagine there are material start-up losses in switching it on and off. So if you know you don't need hot water for the next few hours, switch it off and then switch it back on again when you need hot water again.

[Neverfly]

Hmmm...

I could be wrong on this one, but I'm not quite convinced yet.

In physics, we might say it takes less energy but this is a house we are talking about, and houses are insulated.

So a lot of the application may depend on how well the house in question is insulated.

Also, be wary of the idea that the heater is constantly running. It isn't.

The heater kicks on and off - depending on where the thermostat is set.
So let's say you set the thermostat at 70 degrees F on a cold day.
The heater kicks on- and uses whatever enrgy is required to heat the house to the set temperature. After this- the heater will turn off. It will periodically kick in every once in a while when the house has cooled to the point where the thermostat kicks it on again.
The heater is not constantly running. You are maintaining a temperature differential. Fuel isn't constantly being burned- But it is being periodically burned more often- but in much less quantities than the huge consumption required at start up.

In spite of my making this claim I'm also a big fan of tankless water heaters

[kzb]

Thanks everyone, my own view is that a warm house will lose heat energy at a faster rate than a cold house. That energy has to be paid for, so it can't make sense to leave it on continuously and have a constantly warmed house.

When you start off from cold, yes you need a faster rate of input to get it back up temperature, but whilst it has been cold it has not been radiating as much energy.

I should add, my house is not continuously occupied, we are out at work during the day and we sleep at night. The vast majority of UK dwellings, including mine, are not so well insulated that they will keep confortably warm for very long when the heating turns off. The house is therefore quite cold during working hours and during the night.

[peteshimmon]

It is becoming scary thinking about the cost
of heating fuel in 10, 20 years. I keep
thinking insulating panels fitted inside rooms
will become the rage along with ventilation
trunking fitted with heat exchangers. And
windows kept well shut. It would be great if
fuel used could be cut by many factors this
way yet we still have comfortable homes when
it is very cold outside. With millions of
houses to be fitted out work should start
soon. Also screening shrubs to block north to
east winds.

[NEOWatcher]

I think some of the thinking may come from people with demand meters.

Overall, the less you heat, the cheaper it is going to be, no matter how you do it. This is the physics of it. Now, for the economics.

If any of your heating methods have multiple stages (or the more it has to change, the more power it draws), then the demand may come into play. (I don't know of many heating devices that fit this profile)

I'm not sure how the formulas work (I don't have a demand meter) but it has something to do with the electricity being more expensive if you don't have enough usage to correspond with a large spike in demand.

In this scenerio, the smoother you can make your power usage, the cheaper it is.

[01101001]

Vermont Gas: Automatic and Programmable Thermostats (PDF)

A common misconception associated with
thermostats is that a furnace works harder
than normal to warm the space back to a
comfortable temperature after the thermostat
has been set back, resulting in little or
no savings. This misconception has been
dispelled by years of research and numerous
studies. The fuel required to reheat a
building to a comfortable temperature is
roughly equal to the fuel saved as the
building drops to the lower temperature.
You save fuel between the time that the
temperature stabilizes at the lower level
and the next time heat is needed. So, the
longer your house remains at the lower
temperature, the more energy you save.

Let the temperature drop when heat is not needed.

California Energy Commission: Thermostats

Turn it down. As a homeowner, leaving the temperature inside your home constant day and night will most likely cost you money. It's more economical to turn the heat down when no one is home, or at night when you're asleep. And if your home has a setback thermostat, you've got a simple way to do just that. Used properly, that little box hanging on your wall will save you energy -- and energy dollars.

[Note:] For homes with radiant heating, setting back the temperature for short periods -- such as overnight or during the day when you're away -- is inefficient.

US Department of Energy: Thermostats and Control Systems

(Repeats, probably as source, Vermont-Gas advice above and has this for radiant-heat systems

For steam heating and radiant floor heating systems, the problem is their slow response time: both types of systems may have a response time of several hours. This leads some people to suggest that setback is inappropriate for these systems. However, some manufacturers now offer thermostats that track the performance of your heating system to determine when to turn it on in order to achieve comfortable temperatures at your programmed time.

[Neverfly]

I happily stand corrected and will pass on this correction to the many customers who ask. (Yes, my customers ask this question too )

[Kaptain K]

It must be nice just to have to wonder what's the best way to heat in the winter.
When I left home this morning, the heat was on but inactive.
When I got home, I had to turn on the A/C!
Later this evening, I'll have to turn the heat back on.

[kzb]

It's not that nice Kaptain K ! As I write this it is just after midday here and there is still frost on the ground outside where the sun has not shone. However I will say I prefer this to the usual mild but wet/windy weather we usually get.

I like these discussions, because at least I am now getting some idea, from other the various contributors, as to how this misconception has come about. I don't know if it is just local to around here. But if this is endemic worldwide it makes you wonder about the carbon footprint of what is effectively an urban myth.

[neilzero]

The neverfly explanation has been widly circulated for perhaps a century among well educated people. There may be rare instances where we are better off heating continiously instead of as needed. Steady can increase the average time between equipment failure, but typically it just wastes money and energy. Neil

[Ivan Viehoff]

So this question was about whether we should let the house cool down when we go out for a while, not more sophisticated points. I'm disappointed, especially since Neverfly seems to work in heating and ought to be up to speed on this kind of stuff.

The simple way is to think of it this way. Normally we go out of the house for a few hours, perhaps 3 hours to go shopping, or 10 hours to go to work. But we might go out of the house for a fortnight to go on holiday, or for a year while we take an assignment in another city. The longer we go out for, the more obvious it becomes that letting the house cool down while we are out must save money. Is there any reason to suppose that as the period of absence gets shorter suddenly the argument should change and we should keep the house warm for the period we are out? Plainly not.

The above point I find quite trivial, which is why I looked for more subtle arguments on the cheapest approach to keeping a house warm, during the period we (rationally) want to keep it warm. I considered above the question of a boiler (US=furnace, the above reminds me) which might be inefficient on start-up. In that case, we don't want to turn it on and off too much, would be be better to run the boiler in longer, less frequent, bursts.

Later another subtle issue came to me. Assume no significant imperfections in the boiler for this one. Suppose we want to keep the house at an average of some particular temperature, call it 20C for convenience. The boiler output is not matched to the heat losses, so we use a thermostat to put the boiler on in bursts, and have the temperature cycle. How wide should we set the stops on the thermostat for efficiency? Obviously for comfort we don't want them too wide, but within that constraint, what is better?

Now cooling is generally taken to operate on a 3/2 power law, ie, the rate of heat loss is proportional to the temperature difference to the power of 3/2. In fact heat loss is quite complex depending upon all sorts of local factors, but this is a standard approximation.

Now the question isn't as simple as comparing 20.1 to 19.9 against 21 to 19, because if you have the thermostat ranging from 20.1 to 19.9, it will spend marginally longer cooling from 20 to 19.9 than it spent cooling from 20.1 to 20. So the average temperature will be marginally lower than 20, and this difference will be magnified with the wider range. So that wouldn't be a fair comparison. To compare like with like, we want the average temperature to be the same. So the first part of this computation is to decide what downstop we need to set for a given upstop to achieve an average of 20. The next part of the calculation is to decide whether what you lose on the faster cooling from the higher upstop is regained on the slower cooling to the lower downstop. Rather a tricky calculation involving first solving a differential equation, then inverting a function, carrying out an integration to calculate a mean over a curve, and finally solving some simultaneous equations. I didn't have time to get through it all error-free on the train the other day. Not yet obvious to me what the answer is.

When I got home, I had to turn on the A/C!
Later this evening, I'll have to turn the heat back on.

I wonder in what sense "had to" turn on the A/C. I've been in hotter places than Texas in December with no A/C and I survived perfectly OK. In fact you soon get used to it. Unless we are talking about temperatures higher than blood temperature, being warm is rather different from being too cold, which is fatal unless suitable precautions are taken.

Sounds to me like you need more insulation to smooth out the temperature swings within your building. We think of insulation being important only in cooler climates, but your experience indicates it may be worthwhile in warmer climates also, assuming that there are temperature swings to be evened out.

Neverfly mentions tank-less hot water systems. I assume this is what we call "Combi" boilers, where it heats the water up at the time required. In principle this is energy efficient if you don't often need a tank-full of hot water. But I hate them. The water temperature is typically dependent on the flow rate, they get disturbed by other people using water, and they are generally unreliable.

[Kaptain K]

I wonder in what sense "had to" turn on the A/C. I've been in hotter places than Texas in December with no A/C and I survived perfectly OK. In fact you soon get used to it. Unless we are talking about temperatures higher than blood temperature, being warm is rather different from being too cold, which is fatal unless suitable precautions are taken.

"Had to" in the sense that I crave my creature comforts.

Sounds to me like you need more insulation to smooth out the temperature swings within your building. We think of insulation being important only in cooler climates, but your experience indicates it may be worthwhile in warmer climates also, assuming that there are temperature swings to be evened out.

Actually, my place is quite well insulated for a mobile home. Full skirting and R-26 insulation. My biggest problem is temperature swings. I start to feel cool, so I turn the heat on (raise the thermostat 'til it "clicks"). The heat runs until I'm way past "warm enough", so I have to turn the thermostat back down and the cycle repeats.

[kzb]

[Is there any reason to suppose that as the period of absence gets shorter suddenly the argument should change and we should keep the house warm for the period we are out? Plainly not.

The above point I find quite trivial, which is why I looked for more subtle arguments on the cheapest approach to keeping a house warm, during the period we (rationally) want to keep it warm. [/QUOTE]

I thought it was quite trivial also. I could not think why it would use less energy to keep something on rather than off. However when you have my high school physics teacher plus assorted "experts" in the plumbing and building trades arguing that this IS in fact the case, I thought I had to get to the bottom of it. Believe me, this viewpoint is a widely held belief around here.

Now when you start to go into it, there might be issues around boiler efficiency being different at start-up which might affect the argument. However I would have thought that, in a hot-water-in-radiators system, the gas flame would impart more of its heat energy to cold water than to warm water. This is what a (more efficient) "condensing" boiler does different to a standard boiler. So it should be MORE efficient at start-up, not less. (There might be a problem in a non-condensing boiler with corrosive condensates forming, which of course might end up costing you more money than saving a measly bit of gas).

[neilzero]

In conection with Kaptain K's delema: Why not an I'm cold button and an I'm hot button in addition to the thermostat. The button over rides the thermostat for 5 minutes, which avoids over shooting. It also spares the rest of the family except for the 5 minutes. Of course we could have button wars, just as we can have thermostat wars, but the latter can be costly and uncomfortable for the persons who stop playing thermostat war, while the buttons forget after 5 minutes. Neil

[NEOWatcher]

In conection with Kaptain K's delema: Why not an I'm cold button and an I'm hot button in addition to the thermostat.

My programmable works just fine for this.
Why 5 minutes, why not 10, or an hour?
Instead, with the programmable, if you are a bit cold, you just manually bump the temp a degree or two. Odds are, if you are cold now, you will be cold until the next cycle in the program.

So; I'm cold in the evening, I bump it a few degrees, and everything goes back to normal when I go to bed.

[Neverfly]

After reading the rest of these posts, I don't feel so bad now for having bought into it as well.

And using my car analogy- It does, indeed reason out well.

But as is the case with many things, an analogy is just an analogy- Other factors contributed - and I was wrong.
But neilzero, I didn't invent the explanation I just thought it was true.

Learned about TWO myths in this thread though- Also the 'slaves' building the pyramids. And I got that information from National Geographic years ago- so I thought it was reliable.

I'm wondering now though, as I answer this question correctly in the future- how customers will accept that new information. They may think I don't know what I'm talking about considering
as kzb puts it:

I thought it was quite trivial also. I could not think why it would use less energy to keep something on rather than off. However when you have my high school physics teacher plus assorted "experts" in the plumbing and building trades arguing that this IS in fact the case, I thought I had to get to the bottom of it. Believe me, this viewpoint is a widely held belief around here.

the customers will think I'm full of it. Ugh... What a quandary... When you are trying to build rapport with clients- the last thing you want is them thinking you are full of it.

[Kaptain K]

In conection with Kaptain K's delema: Why not an I'm cold button and an I'm hot button in addition to the thermostat. The button over rides the thermostat for 5 minutes, which avoids over shooting. It also spares the rest of the family except for the 5 minutes. Of course we could have button wars, just as we can have thermostat wars, but the latter can be costly and uncomfortable for the persons who stop playing thermostat war, while the buttons forget after 5 minutes. Neil

I guess my problem stems from the fact that I have electric heating. There is a pretty severe lag between input and change in output. When I turn up the thermostat, it's about 15 seconds or so before the fan kicks in, which isn't too bad.
The problem is that when it gets warm enough and I turn the thermostat back down, the fan keeps blowing for about five minutes (to cool of the heat exchanger?). By the time the fan shuts down, I'm sweating! It gets to be a guessing game as to when to shut it off to achieve the "right" temperature.
Fortunately, I live alone so I don't have to worry about "thermostat wars".

[Van Rijn]

I guess my problem stems from the fact that I have electric heating.

Is that a heat pump or pure resistive heating? If resistive, ouch! Small story: Back around '70, my family had a "modern" house with resistive heating panels . . . in the ceiling! There was an awful temperature gradient from the floor to the ceiling, and I remember dad complaining about the electricity bills even in those days. The only plus is that each room had its own thermostat.

There is a pretty severe lag between input and change in output. When I turn up the thermostat, it's about 15 seconds or so before the fan kicks in, which isn't too bad.
The problem is that when it gets warm enough and I turn the thermostat back down, the fan keeps blowing for about five minutes (to cool of the heat exchanger?). By the time the fan shuts down, I'm sweating! It gets to be a guessing game as to when to shut it off to achieve the "right" temperature.
Fortunately, I live alone so I don't have to worry about "thermostat wars".

My gas heating system runs the fan for a bit too. There is still warm air in the ducts as well. Though, it doesn't overshoot the thermostat much.

[publius]

The problem is that when it gets warm enough and I turn the thermostat back down, the fan keeps blowing for about five minutes (to cool of the heat exchanger?). By the time the fan shuts down, I'm sweating! It gets to be a guessing game as to when to shut it off to achieve the "right" temperature.
Fortunately, I live alone so I don't have to worry about "thermostat wars".

Google "Heating anticipator" for solutions to that little problem. Now, a modern super duper eeee-letronick brain thermostat may do that electronically, but they should be adjustable.

With the older simple thermostats, you had a little resistor that adds "false heat" to the bi-metal element, causing it to shut off a little before the actual set point open temperature is reached. That has to be adjusted a little in the field for each application. When adjusted right, the temperature should reach the labelled set point after the "cool down" period.

-Richard

[danscope]

Pretty cold (for us) in England currently, and I have been having an argument about heating costs.

Some people say that it works out cheaper to leave the central heating on all the time. Or alternatively, set the timer so that it goes on-off-on-off in a 15 minute cycle.

Now this seems bizarre to me, but the thing is I have heard it several times over the years from different people.

Also when I was at school (longer ago than I care to mention), our physics teacher, no less, stated that you should leave your hot water immersion heater on constantly, again because it used less juice that way.

I can't see how these ideas can be true, but nevertheless they seem to have widespread support in the population. So the questions are

Are these things true?

If so, exactly why?

If NOT true, how did these ideas gain support in the population?

Thanks

**************
Hi, If you want to enjoy your heat at night,...and pay a little less for the privilige, make yourself some thermal curtains for your windows, which will reduce the cold convection currents ...cold air falling off the face of your
window panes. And...if you don't have any insulation in the walls...
GET SOME. You will have a hard time heating an uninsulated house.
It doesn't pay. Once you have tackled these problems, and seen to your door trim gaskets (neoprene strips ) ...weather stripping....now your house is reasonably tight. You don't want a house that is tight as a watch. That makes a " sick" house. You house still requires an air change every so often.
Many homes employ an air-to-air heat exchanger which warms up incomming air with heated exhausting air. Saves you money. Also, houses with basements enjoy thermal radiation from the ground, which is always 50 degrees. A home built on a slab does not enjoy this feature and will always be harder and more expensive to heat.
I leave my home at 69 degrees and enjoy the heat I paid for.
Take a stick of incense and do a sniff test of the drafts of incomming air.
The smoke from the incense will be drafted by any substantial breath of incomming air. Clean the area, and use silicone seal (rtv caulk ). This cuts it down quite a bit.
Windows. Remember: Nothing sticks to plastic wrap (saran wrap, reynolds...cling etc. So, armed with this knowledge, you can lay a strip of plastic wrap along the bottom of the window sash, and run a good bead of silicon caulk along the bottom of the sash and then close the window. Tommorrow, open the window and peel the plastic wrap ( comes off easily ) and now, you have a tight bottom on your sash. Don't do the side of a sash. This will not work, and neither will the sash.
Once you have secured the severe infiltration, your house will stay warmer
longer. It's like having a boat with holes in the bottom. Bailing is part of the answer. Plugging the holes to something managable is the best answer.
Same heat lasts longer.
Be sure that your heating system is working properly and that it is getting it's required air supply and draft. Your heating man should inspect your system
at least annually. My technician uses a computer to anylize the stack gases
and determine plant efficiency once the burner has been satisfactorily serviced. And always be certain that your heat exchanger is as clean as possible. This is where the heat you generate gets into the medium which moves the heat, ie steam, hot water or forced hot air.
If you have a gas plant, it always stays clean. Still, have it inspected at
intervals.
By the way: When ever I am getting a bad storm....ice storm, blizzard,
wet snow, high wind, I know there is a potential to lose power....and my heating plant. I set my thermostat higher on those occasions, where as
the warmer my house is, the longer it stays warm untill the power comes back on. When desparate, I use the fireplace, but not untill the house get's
colder. This requires a drain down of the plumbing....if it gets down to near freezing. Not good but....it's an emergency. Save the pipes.
This is very rare,however. I have yet to require it in 35 years.
Good luck and stay warm.
Best regards, Dan

[Jens]

the customers will think I'm full of it. Ugh... What a quandary... When you are trying to build rapport with clients- the last thing you want is them thinking you are full of it.

That seems fairly negative. You said earlier in the thread that customers "ask about it all the time." If they ask about it, it must mean that they are unsure. So I don't see why they would think you're "full of it." They presumably want to hear a "professional view."

[Neverfly]

That seems fairly negative. You said earlier in the thread that customers "ask about it all the time." If they ask about it, it must mean that they are unsure. So I don't see why they would think you're "full of it." They presumably want to hear a "professional view."

Customers ask questions, yes. People want to hear what they want to hear.

Trust me- with years of experience under my belt - people will ask you something, and you will revisit them a year later, and they will ask the same question again. They never changed.

They ask questions testing your knowledge, but they don't know the answers either usually, so it isn't really to test your knowledge as much to see if you SOUND like you know what you are talking about.

If a customer likes you, they will pay you

All of it has less to do with reality and more to do with myths and perceptions. It's sad, but it is they way it is- all you can do is try to win them over in the first two minutes. Then get to work- get finished - get to the next.

Occasionally you get a customer that listens or is knowledgeable or better founded in reality- but after many repeat housecalls and visits, i can assure you, they are rare.

[kzb]

Thanks Danscope. I've just had double glazing put in (very draughtproof frames), the loft is insulated, the only thing left is cavity wall insulation, which I think is relatively cheap. But that's made me think of something else.

All houses (in UK anyway) are festooned with ventilator bricks on the outside and ventilator grills on the inside walls. As well as letting in the spiders, it is seen as supremely important that your cavity walls are ventilated.

However, as soon as you have cavity wall insulation, that idea goes out the window. In fact the vents have to be blocked, to stop the foam jetting out before they do it.

It's also seen as supremely important to have massive ventilation in the loft if it is insulated. This again seems counterproductive to me, and a slate pitched roof is not going to be exactly air tight is it.

Another point is gas fires. The nation has largely changed over from the radiant design to coal-effect design. What's more, I tried to get a new radiant fire last year and I could not find one that you could turn down to just the central radiant. Coal-effect fires are almost universally inefficient compared to the old radiant fires, so what has this done to the carbon emissions? But you never hear anything about that.

[danscope]

Hi, Sounds like some excellent questions. I am not familiar with some
situations peculiar to the UK. The attic ventilation will make the roof last. That is certain. In America, we now cut a ridge vent in the very top of the roof peak (ridge) which then recieves a special polythene sponge like material which
sheds water, but allows heat to escape.
Brick wall systems in severe humidity climates are another science.
I should read up very well indeed before sorting out wall insulation. The experts,
especially the government sites should give you the best, honest information.
I dislike spiders, but welcome them "Outside". The removal of flies will eensure the disappearance of spiders, which feed on them greedily. No flies..no spiders.
My own heating system is forced hot water. I have never used portable
heating devices in my home. The better ones I have seen were oil filled with the heating element warming the oil to generate heat. I believe that these units are safer , provided that they have a good, heavy duty electric lead (cord ).
We see a lot of gas fire log systems being installed in fireplaces. They are not cheap, but seem to be very convenient, and even work with a remote control.
Remember: Safety comes before convenience or economy. Always.
Best regards, Dan

[peteshimmon]

Another aspect of this subject should be
mentioned. We were spared a heatwave this
summer in the UK but they are getting
generally hotter over recent years. A well
insulated north facing room with double
"airlock" door entrance would make a nice
refuge for some people. Folks are buying
room air conditioners more but they have to
work hard for conventional houses. Such a
room as I describe would be easier to cool.

[danscope]

Hi Pete, And may I add that an individual room airconditioner is BETTER than central air . Much better. Duct work can harbor spores, mold, etc and is nearly impossible to completely clean. An individual unit can be removed, thoroughly cleaned, refurbished or replaced at your convenience. This works.
Best regards, Dan

[ToSeek]

The first year my wife and I lived in our present house, we turned the heat down every night and turned it up again in the morning. After one winter of the house being unlivable until lunchtime, though, we decided against repeating this approach. However, we used far less electricity (by a very significant margin) that first winter than in the subsequent ones.