Turn thermostat down or leave steady?

[Stormin Mormon]

Either one. My answer is the same. Lower temp means less heat used.

[Tony]

In most applications it saves energy to turn it down. However if you have a heat pump, and to get the house warmed up again it goes to emergency heat, then it can cost more. If you can turn off the emergency heat and wait a long time for the heat pump to catch up, then you will save energy. The worst case is electric emergency heat, gas emergency heat may or may not save money depending on the price and efficiency of the furnace. Although it just occurred to me that you asked about conserving *energy* and not *money* so that may mean that no mater what your heating system is, turning it down then up again will always save *energy*... I think?

[Tony]

I believe in your situation it will still save energy. The reason they tell you to "set it and forget it" is for comfort. Due to the large mass of your system it will have a much slower recovery time, but that does not mean it will take more energy, it's just slower. Or you could turn it down hours before leaving and have it turn on hours before arriving home again. That should help with the comfort.

[Walter R.]

No surveys or studies needed to address this question. The Second Law of Thermodynamics decrees that the speed and extent of all heat transfers in the universe depends solely on the temperature differential between two objects. The moment you turn down the thermostat you start saving money. The longer you keep it down, the more money you save.

For further musings:

[mm]

Why did you assume the Mormon had a boiler?

It costs that same fortune and more to keep it hot without interruption. Maybe it's also unpleasant becuase it takes hours to heat up, but that's another story.

[mm]

Yes, and you lose some of what you saved 9 hours earlier when it started to cool off.

What you don't lose is the heat that wasn't radiated, conducted, or convected from the house because the house spent most of those 9 hours at a lower temperature.

If the house is 68 degrees, a certain amount of heat escapes. When the house is 55 degrees, a lower amount escapes. If the temp outside is 56, maybe no more heat escapes than enters. So you save the fuel that would have been needed to make all that heat.

BTW, my mother always turned the heat down at night to save money. There were no setback thermostats then, so she got up in the cold, put on a flannel robe, and turned the thermostat up and tolerated it until it got warm again, maybe 15? minutes with forced air heat. The only reason not to is the period of discomfort, but with setback thermostats, at least on days you don't get up or get home early, it will turn on the heat in advance.

[Stormin Mormon]

Still, it's less energy used cause less energy is lost.

[mm]

No it won't, but what about when boiling water. Shouldn't the temp be all the way up when one is in a hurry? Even though on my electric stove with a medium sized pot of water, water will continue to boil when the knob is at 6 out of 10.

That would be bad. I have so much junk piled there, I can barely get within 8 feet of my thermostat.

[mm]

I drove my brother's car for two days last week and he has automatic cc. It was 70 degrees out, and I opened the windows, but I still wanted air from the blower vents. But afaik, I had no way to set the air temp like I can do with my simple non-auto heater.

Is there a way to do that. He has a Lincoln.

[mm]

So if you are gone a long time it's six, and if gone a short time, it's half a dozen?

ARen't you thinking of gas mileage?

I will. All the extra things you mention, walls etc. are included every step of the way. So it saves money to turn down the heat.

[dpb]

mm wrote: ...

Specifically on FMCo products I don't know but GM/Chrysler have a pretty simple/intuitive interface to set the desired temp w/ a manual/auto override function...

[mm]

I restored part of it to also email it to a friend of mine, who complained about the same thing once.

My friend who used to have a Cadillac, in the 80's I think, complained about the same thing, but that was maybe 20 years ago. I'm glad to hear there is way to override this on some cars. And a simple way too. That's wonderful.

He advised me not to get auto, and it certainly seems to miss the point when auto is great with the windows closed, but inferior to manual with the windows open (or the top down in my case.)

[sligoNoSPAMjoe]

It would be difficult to answer that question. It is more complex than it might appear at first.

If you are talking about resistance electrical heat only, then you would always save energy by turning it down. However most of use heat with heat pumps, or gas, or oil, some may use ground water or not. Even the effect on the power grid could be a factor.

In addition you need to consider the comfort and ease of use your choices may change.

Like most all things in the energy world, the answer is complex and not alwasy what appears correct.

[DD_BobK]

Wrong answer! Check previous threads on this topic.

So by your reasoning if you turned down the heat to 50F & left it down for a week....you wouldn't save any energy because you'd have "add back all that heat"?

cheers Bob

[RickH]

What happens when he comes home and turns it back up again? The reverse, so where is the savings?

[RickH]

Hot water heat is very popular here.

[DD_BobK]

So the laws of themodynamics are different from system to system?

Heat its lost to the environment based on the difference in temperature between the heated space & the unheated space. As the temperature of the heated space falls, the heat loss also fails. When the temperature of the heated space falls to that of the unheated space, heat loss stops.

I believe you are confusing the "time" it takes to recover with "huge amounts of energy are required to re-heat everything".

If you were correct in your thinking (& oyu are not) the whole concept of temperature setback would not work (& it does).

cheers Bob

[DD_BobK]

wrong...too much work to convince / educate you

cheers Bob

[Mark]

The above is the CORRECT answer... congratulations!!

Mark

[Tony Hwang]

Hi, Many programmable thermostats are intelligent. It learns when to start to bring up the temp. to normal setting ahead of time. So by the time people come back home/ofice after et back period it's at proper temp.