Not sure that's resolved - would be really nice to!
A quick search I did seems to support it IS better to turn heating off when you don't want it, & on when you do, (AND HIGHLY recommends very programmable heating programmers, many time periods at different temperatures etc). Because, as others have pointed out here, the higher the temperature inside, the greater the heat loss to the outside.
For example:
http://www.grist.org/article/advanced-degrees
Dear Umbra,
Many of my friends are environmentally minded and do lots of things to try to have a smaller carbon footprint. Yet when I tell people I turn my heat down when I leave the house even for an hour or two, and that I turn it down to 50 at night, they say, "I thought it takes more energy to reheat the house than to keep it at a constant temperature." Please clarify. If it is better to turn the heat down, then there is a LOT of room for education on this topic, as even many people in the environmental community are confused.
ANSWER
Let's say a typical, nice heat setting is 68 Fahrenheit while at home, 58 at night or while away. (Your 50 is probably lower than most people will try, but bravo to you.) The heater will save fuel as it falls to 58, and expend about the same amount of fuel as it rises back to 68. Therefore, these two transitional phases cancel each other out. And while the heater is set at 58, for as long as it is set at 58, it is merrily saving fuel (aka energy, money, and the planet). Because as we all know, it takes more heat to keep a house at 68 than at 58. Overall, then, fuel is saved.
To bulk up this answer a little bit and remind us all that insulation and sealing the house are important aspects of keeping ourselves, but not the planet, warm, let's discuss air-movement dynamics briefly. Remember, air lives a life of heat equality. Hot air wants to rush out and share the heat with nearby cold air until all air is the same temperature. This happens, as fervid readers may recall, through the processes of convection, radiation, and conduction. The stack effect is an example of convection: Hot air in a building not only rises, but is of higher pressure. As it rises, it pushes against any cracks in the ceiling or roof, escapes, and leaves a low-pressure area at the bottom of the house. The cold air rushes in to the low-pressure area, and must in turn be heated.
Our heaters are fighting an incessant battle on our behalf, warming all the new air. If we are not there to be warmed, or are sleeping under a cozy duvet, we can turn down the thermostat. Programmable thermostats are very helpful and quite cheap.
I repeat: Reheating uses less energy than keeping it hot while you're gone. No organization -- reputable or disreputable -- disagrees with this advice. To quote the EERE, "This misconception has been dispelled by years of research and numerous studies."
One link quoted supporting this view in one the replies might have clinched it
“If you want to really nerd out over this here is most recent, over-instrumented research:
http://www.homeenergy.org/article_full.php?id=566&art ...”
but frustratingly, won't work for me!
ALSO: extracts from the EERE advice:
http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12720
“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. In fact, as soon as your house drops below its normal temperature, it will lose energy to the surrounding environment more slowly. The lower the interior temperature, the slower the heat loss. So the longer your house remains at the lower temperature, the more energy you save, because your house has lost less energy than it would have at the higher temperature. The same concept applies to raising your thermostat setting in the summer; a higher interior temperature will slow the flow of heat into your house, saving energy on air conditioning.”
[Unfortunately I am then lost, when EERE advise states:
Limitations For Homes With Heat Pumps, Electric Resistance Heating, Steam Heat, And Radiant Floor Heating
Programmable thermostats are generally not recommended for heat pumps. In its cooling mode, a heat pump operates like an air conditioner, so turning up the thermostat (either manually or with a programmable thermostat) will save energy and money. But when a heat pump is in its heating mode, setting back its thermostat can cause the unit to operate inefficiently, thereby cancelling out any savings achieved by lowering the temperature setting. Maintaining a moderate setting is the most cost-effective practice. Recently, however, some companies have begun selling specially designed programmable thermostats for heat pumps, which make setting back the thermostat cost effective. These thermostats typically use special algorithms to minimize the use of backup electric resistance heat systems.]
ALSO: advice from the UK Government's Energy Savings Trust:
http://www.energysavingtrust.org.uk/In-your-home/Heating-and-hot-water/Thermostats-and-controls
“Programmer or time control
This will automatically switch your heating off when you’re not at home, or when you can do without it, such as when you’re in bed.
Programmers allow you to set ‘on’ and ‘off’ time periods. Most models will let you set the central heating and domestic hot water to go on and off at different times. There may also be manual overrides. Check that the timer on the programmer is correct before you set your programmes. You may also need to adjust it when the clocks change.
Choose a cold evening and time how long it takes for your house to warm up from cold to a comfortable temperature – this is the warm-up time. Then turn the heating off completely and time how long it takes for the house to start to get uncomfortably cold – this is the cool-down time.
You can now set your timers including the warm up and cool down time. So, for example, you can make sure that the heating goes on with a warm-up time before you wake up and turns off before you leave the house. If you insulate your home, it will warm up more quickly and cool down more slowly, so you’ll save money on heating.”
Please note however:
the EST advise says allow for the warm-up and cool down times.
Clearly, if your house / heating system is such that the warm-up period is longer than a period you leave then return to your house, then you can't turn the heating off (and expect the house to return to a comfortable temperature when you want it to). You'd need to turn the thermostat down to whatever the heating system can recover from, when you leave.
If this is the case, then we are dealing with “extreme” cold and / or relatively poor house construction (or possibly high heat expectation).
I think Paul's point:
“And .... I stand by my point that it takes much more energy to warm a home 15 degrees than 2 degrees.”
is certainly true, but the logic wrong, since you've been paying (using energy) to keep your home that extra 13 degrees warmer.
HOWEVER:
(I am a home energy advisor in the UK, so have this discussion quite often) I do meet some people who claim they have tested this and found that they use less energy keeping their house on a mid-temp “tick over” while they are out, then boosting it up when they are in, rather than letting the house go “cold” (I am assuming not freezing).
I can only accept what they say, though it does not fit with what I can justify to myself, nor what “official” guidance seems to be, both in the UK and US.
Other considerations:
Paul is no doubt aware of Ianto Evans' thermal benches / beds and the like – heating furniture (rather than the surrounding air) seems a more sensible way to go, ESPECIALLY when burning wood, because the most efficient burn is a very hot burn, so the deal there is to store and moderate the heat (which massive furniture allows).
Mass furniture is unlikely to be acceptable in most modern (i.e. light-weight homes, where I suspect load-bearing capacity is a limiting factor)
Obviously we don't want our homes to freeze (burst water pipes). Modern heating programmers should include a frost setting, which will prevent indoor freezing - clearly sensible.
And yes (of course):
it is far better to only heat those areas of the house where you are (i.e. not “spare / guest bedrooms...”),
and, more extreme, but I think entirely logical, Paul's personal heating (rather than space heating), e.g. as simple as a blanket on a couch, as per your great “how I saved 87%..." article
Most of us in Europe have got used to very cheap heating, mainly from natural gas which is now getting less cheap, so I think the days of central heating (i.e., in my opinion heating under-used areas of a house) are numbered. In my childhood (I'm approaching 50), my family, who I wouldn't describe as poor, had just one heated room (in addition to the kitchen, which was warm while cooking was happening). I htink this was normal.
So in winter, we were mostly in the (one) heated room. I didn't spend too much time in my bedroom in deep winter, which could get ice on (the inside of) the windows.
Bodies are likely to radiate around 100watts / person, so a few people in one room begins to make a significant heating impact.
