Do you save energy by lowering your thermostat when you are not home and then raising it when you get back?

Question

i have heard different sides to this question. I have heard that you will save money if you lower the thermostat in your home during the day while you are at work, but i have also heard that it doesn't save money because you use more energy trying to raise your home's temperature, and you are better off keeping your thermostat at a consistant temp. for refrence in our situation, i was going to lower the theromstat to about 62 during the day and raise it to 68 when we get back home.

Answer 1

This is an answer that I left for another very similar question concerning set back of thermostats. It will definitely save money to set it back since heat loss is proportional to the temp difference between inside and outside......see below

There are highly technical answers to this question that are based on the science of heat transfer, but to simplify things, basically that heat loss is proportional to the difference between the outside temperature and the inside temperature. So if the outside temp is 30, and the inside temp is 70, you will have a 40 degree difference.

Likewise, if the outside temp is 30 and the inside temp 60, the difference will be 30 degrees. 30/40=0.75, or you will have only 75% as much heat loss at 60'F than you would have at 70'F.

This "savings" is true for only as long as the time period these conditions exist whether it be 1 hour or 24 hours and it is a real savings dispite the fact that you have to heat the house back up, which then increases the difference in temperature and increases the rate of heat loss. Whether the furnace is on or off does not figure into the heat transfer equation. Only the difference in temperature does.

So, the smart way to run things is to determine when you want your house temp at 72 degrees F, lets say, 7am and turn off the setback the exact time it takes to heat the house to 72 degrees F. If that is 3 hours as suggested, if you turn off the setback at 4am, the house will be nice and cozy at 7am, and you WILL have saved energy. Even during the reheat period you save energy until the temp gets to 72'F, because at 70degrees F the temp difference to the outside will be less than at 72 degrees F. Temp loss does not depend on whether the furnace is on or off, just the diff in temp between the outside and the inside.

There is one other thing that can be done also. Humidity in the air makes the air feel hotter. That is why on a very humid day in the summer you feel hotter than on a "dry" day. It's why people talk about "dry heat" during the summer vs humid air.

You can use this to your benefit during the winter also. By humidifying the air you can decrease the temp setting and still be comfortable. In doing so, you will decrease that temp difference between outside and inside and therefore slow the heat loss. If you start getting condensation on windows you have gone too far. Another highly efficient form of heat loss comes into play if you start getting condensation.

Condensation heat transfer is much more efficient than the sort of heat transfer that occurs from the air in your house to the air outside the house, so back off the humidity if you are getting condensation on the windows.

I would also like to stress that I am not saying you will save 25% on your bill. For a home, the heat loss formula is constantly changing simply because the outside temperature changes. The savings would also only be 25% if you kept your house at 60'F full time, so if you are only doing this 4 hours of the day the amount saved would be 25% * 4hr/24hr = 4% savings on the bill. Also, as the temp difference gets higher the percentage of savings decreases, although you are still saving the same number of dollars. (If there were a 100'F difference between the inside and outside at 60'F, such as in the Arctic vs 110 'F at 70'F you would save only 10% instead of 25%,and if that were for only 4 hours a day it would equal a net savings on the bill of 1.7%.

Other "heat transfer" variables can also come into play, such as wind velocity which increases turbulance and increases heat loss, rain, snow, direct air leakage, opening and closing of doors, etc.

Answer 2

You absolutely do save by turning it down when you don't need it.

Sometimes, if you make the situation extreme, it's easier to visualize.
Imagine being gone for a week, and turning the heat down to 55F....when you come back, let's say it takes 2 hours to heat the house back up. If the heat had been left on 70F all that time, it would have run more than 2 hours to maintain that temp over that time.

Another factor is that the insulation and windows in the house lose heat faster if the difference between the inside and outside is greater. Again, making it extreme...if the outside and inside temps are exactly the same, there is zero heat loss. As the difference becomes greater, the RATE of heat loss also becomes greater. It takes more energy to maintain a temperature difference of 60 degrees than a difference of 45degrees.

To add in another reason...if your furnace doesn't have to turn on and off as often, it saves money because motors take an extra jolt of electricity just to start. If they don't have to start as much, they don't take as much power.

Furnaces don't "run harder" if they run longer. They run at the same rate, it's not like the gas pedal on a car.

Ya dinna can deny the laws O' physics...

Answer 3

If the temperature that you set your furnace at, is stable for 8 hours and you are comfortable within the home..leave it alone. If you feel chilly when you enter your home and need to turn up the heat for an extra 6 degrees, leave it there. Once the home temp. stabilizes, the furnace should cycle only when it needs to. The key is to find the temperature that makes you comfortable and allows the furnace to cycle as few times as possible. The furnace will kick on sometimes as soon as you open the door, ignore that as it's just doing it's job. If your home isn't insulated properly, your furnace with constantly be trying to compensate for the temp. change. If your home is insulated really good, buy a Carbon Monoxide Detector because gasses can't escape because of the quality of insulation application.
Bottom line...Insulate well, find a comfortable temperature, leave the thermostat alone.

Answer 4

In the summer it does save you a little money to raise the thermostat 2 to 4 degrees while you are not home, but in the winter it takes more energy to heat than to cool, so it doesn't save you as much. Set the thermostat at the desired temp while you are at home and turn it down 2 to 3 degrees while gone. It also depends on how well insulated your home is as to how much it will save you. If you have an older home it is suggested that you add insulation to the attic space as well as the walls. You can have someone come in and blow it into the attic and walls. They suggest 4 to 6 inches in the attic and have the walls blown full.

Answer 5

It really depends on how low you go, and the size of your home. If you have a large home, and you turn it off or too low, it can use a lot of energy heating it back up. If you have an average home and lower the thermostat by 5-7 degrees, it will save you money in the long run.

Answer 6

U will save money period. The recovery to heat up 6 degrees is minimul to say the least. Also look for other areas to conserve, insulation, lower wattage or energy blubs, larger loads of laundry, caulking around the windows and doors outside etc. Good luck with your saved $$$$$$$

Answer 7

i dont think it saves any because when you get home and raise the thermostat it takes some energy to bring it back to the place where it sopposed to be so if you left it at the right temperature everything should be ok when you get home.

Answer 8

Actually the power companies call for doing just what you have decided!

When the weather is neither too hot or too cold, I turn my system OFF during the day and just leave my ceiling fans on to circulate air....unbelievable how low my bills have been.

Answer 9

you should be able to set the clock for the boiler to only come on before you wake till wen you leave for work and then off untill just b4 u get bk from wrk so the house is toasty for you. it will either be a anolgue clock that looks like an egg timer with little tiny switches all around it or a digital 1 with sliders for continuos and therostat control or off. and the same for hot water.

Answer 10

For AC electric companies suggest for the best energy savings that you have it at 83 when you are gone and 78 when you are home.