Setting back the temperature for a given "X" hours

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Old 11-13-05, 12:56 PM
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Setting back the temperature for a given "X" hours

This is one of these questions like that James Dulley syndicated newspaper columnist likes to answer.

Is there some rule of thumb, in general to how long one needs to turn the thermostat way down, when you go to work, so that when you get back home, you wil have saved money by not having left it where it was?

Like, you had it at 75. You go to work at 8 am and turn it all the way down so that it won't come on unless the temp hits say about 50-55 degrees. And you get back home at 5:30 that night.

Ar you going to save any measurable amount by doing this? Or, is there a potential folly here where this is perhaps harder on your system? Or, is it EASIER on you system (less cycles)?

Is the size of the house going to affect this, or not (due to the fact that the furnace sizing and house size forms some sort of ratio? Or, a person who has a house filled with objects that absorbs heat as opposed to someone with a real empty looking house.

I love experimenting with stuff, but to actually perform a rigid test where the outside temp and conditions are the same, for say a week, so you could switch back and forth to doing it one way and doing it the other way seems almost impossible. Either it is sunny one day with no wind, or cloudy another day and colder, or partly cloudy with wind, or the temperature changes a lot...etc.
 
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Old 11-13-05, 05:45 PM
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I should have my own syndicated column too. It would be easier on my back than actually doing the work. That has no relevance to anything but I wanted to say it.
I remember in the 70s that Honeywell said if you turned back your thermostat by 10 degrees for 8 hours, you would save 10%. I have never seen that written so you may have to take my word for it unless someone else chimes in here to agree or disagree. What that would boil down to is if you went to work and turned the heat down to 58 from 68 and would have used 1/2 gallon of oil to keep the house warm all day, at $2.00/gallon you just saved 20 cents. If you did it when you went to bed too, you could save another 20 cents. When you flesh it out, it may be a long time before you pay for the setback thermostat in savings of fuel. What really helps is insulation and keeping the heat as low as possible all the time.

Ken
 
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Old 11-13-05, 05:57 PM
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if it is a gas unit them it will save you money.
 
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Old 11-13-05, 06:13 PM
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Unless gas has a time-of-day rate it wouldn't matter what fuel you use. The amount of energy needed to restore the building to the original temperature would remain the same. If it was done with electric on the time-of-day rate and you turned the heat down during the last 8 hours of the day rate and turned it up after the night rate was in effect, there could be more savings there.

Ken
 
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Old 11-13-05, 06:22 PM
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But if it was a heatpump it would be more economical to let it hold the temp than to turn it down then make the electric heat bring it back up.

I gues I should have said any single stage unit will save you money by turning it down.
 
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Old 11-13-05, 06:44 PM
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I always wondered on the heat pump setback thermostats with adaptive intelligent recovery, if they have to raise the temperature so slowly, how long does it actually stay down at the lower setpoint? It seems that at the rate of recovery you would get out of a heat pump in 20 degree weather, you would have to start back up after about 4 hours and spend the next 4 hours inching toward the upper setpoint. I guess if there is a demand for a product, someone will produce it.

Ken
 
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Old 11-13-05, 07:10 PM
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The amount you save when the temperature is falling is pretty much equal to the amount it costs you to bring it back up. The savings is the time spent at the lower temperature. If your house is at that temperature for a decent amount of time, there will be a savings. If the temp starts going back up shortly after reaching the lower temp, you won't see a difference in the bill.
 
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Old 11-13-05, 07:48 PM
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I believe there are to many determining factors to accurately say whether savings will be noticed or not.

I always tell people that if it is just for the day leave it, if you are gonna be gone for a week then turn it down.
 
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Old 11-14-05, 05:00 AM
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Originally Posted by shank
I always tell people that if it is just for the day leave it, if you are gonna be gone for a week then turn it down.

Bingo. In my opinion you're not going to save much at all and h/p's "older" will cost you because the strip heaters are going to kick in full force.
 
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Old 11-14-05, 04:25 PM
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Originally Posted by KField
Unless gas has a time-of-day rate it wouldn't matter what fuel you use. The amount of energy needed to restore the building to the original temperature would remain the same. If it was done with electric on the time-of-day rate and you turned the heat down during the last 8 hours of the day rate and turned it up after the night rate was in effect, there could be more savings there.

Ken
Last year I told this very thing to a woman who was trying to save on her electrical bill (electric baseboard heating) who had that interupter device from the power company; On-peak/off peak".
 
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Old 11-15-05, 02:19 PM
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I think a person can save on set back (Gas/Oil Heat) as long the equipment is sized right and t ightness of the home.

I kinda did a test with my house and my neighbor when I used to live in a mobile home.. Both of our homes were pretty much the same lay out and what not..

he would keep it at 70 at all times.

I would do the 55 at night, 68 wake/home, and 55 gone..

I also had a gas dryer, he did not..

My savings were about $20 a month savings..
 
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