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Old 12-28-2005, 04:31 AM
dauerbach dauerbach is offline
Join Date: Dec 2002
Posts: 2,335
Lowering thermostat to save money

My gas bill was high (no surprise there) and someone recommended lowering the thermostat set point. I wonder if this will really save any significant amount of money. My thinking is that say it is on average 35 degrees outside. While it will take more energy to raise the temperature in the house to 72 rather than 65, it seems to me that after either temperature is reached the amount of energy to keep it steady should be the same. Why would it cost more to KEEP it at 72 degrees? If it really does, how much does one save for each degree the thermostat is turned down.
Old 12-28-2005, 05:45 AM
The Controvert The Controvert is offline
Join Date: Sep 2001
Location: Austin, TX
Posts: 3,757
The rate at which the temperature in your home drops is directly proportional to the difference in temperature between the inside and the outside.

This should be intuitive by consideration of extremes. Assume a metal box is placed outside and is not being actively heated. If it is 35 degrees outside and interior of the box is at 36 degrees, after one minute, the interior temperature will drop by a fraction of a degree.

Now, if the interior of the box is at 700 degrees, after one minute, the interior temperature will probably drop by several degrees. QED

The difference in temperature is greater at 72 than at 65, therefore, more energy is needed counteract the dropping temperature in your home at 72 than at 65.
Old 12-28-2005, 05:52 AM
ticker ticker is online now
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Location: London
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To add to what The Controvert said:

The reason hot things feel hotter than cool things is that they are transferring, and therefore losing, more heat. If your house is hotter then it will be losing more heat to it's environment. To maintain this higher temp your heating system must replace this lost heat more quickly and thus burn more fuel.
Old 12-28-2005, 06:17 AM
dauerbach dauerbach is offline
Join Date: Dec 2002
Posts: 2,335
First, googleing brought up wildly disparate numbers, with some experts ridiculously stating that you could save 50 % of your heating costs by turning the thermostate from 70 to 60 such as here:

I don't think your example is salient. We are not talking about free transfer of energy, but rather the percentage loss from a highly insulated structure. I don't doubt that there must be some savings, the point is, if it amounts to 1% a month it's not worth the inconvenience of being constantly less than comfortable. So perhaps I should more clearly ask, how much energy is being saved by dropping the thermostat, say 5 degrees, with an average outside temperature of 35 degrees, assuming the house is fairly well insulated.
Old 12-28-2005, 06:50 AM
Geochelone Geochelone is offline
Join Date: Dec 2005
Posts: 3
Heat transfer is defined by Q=UA(T2 - T1)

For your situation U,A and T1 are defined. The additional energy (cost) required to heat your place to 72 v 65 is therefore (72-35)/(65-35) x 100 - 100 = 23%

So you can save 23% on your fuel bills by reducing your temperature from 72 to 65.
Old 12-28-2005, 10:00 AM
Zsofia Zsofia is offline
Join Date: Feb 2001
Location: South Carolina
Posts: 24,534
I went from a traditional thermostat, trying to keep it down at night and when I was at work myself, to a programmable one, last month. When I'm at work and asleep it's on 62, 70 when I wake up and 68 when I'm at home in the evening. Nothing else changed, but my heating bill went from 142 to 115. The plural of anecdote is not data, but I'm very happy with turning down the thermostat.
Old 12-28-2005, 10:33 AM
Tastes of Chocolate Tastes of Chocolate is offline
Join Date: Aug 2003
Location: slightly north of center
Posts: 4,479
Xcel Energy has an online calculator. You fill in some basic info about your house, the temp you are at and the temp you want to calculate for. There is no place to go into your current insultion, cost of natural gas, etc, but as a very rough estiamte:

Per that, for a 2000 sq ft, 3 bedroom house, if you were at 72 degree F, and go to 67 degree F, all day and night, you would save between $200- $300 US in a year.
Old 12-28-2005, 10:41 AM
aahala aahala is offline
Join Date: Mar 2002
Posts: 1,781
dauerbach, by my calculations and the current price of NG, if you live in the US and lower the temp 7 degrees, you will save about $2,800 over not doing it.
Of course, you will still be paying 40% more than last year's heating bill.


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