Most efficient thermostat setting?

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Old 01-01-09, 09:21 AM
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Most efficient thermostat setting?

I have a new Trane variable speed gas furnace and live in Atlanta, GA area. I set the thermostat down to 58 at night and when I'm gone during the day, then up to 67 thirty minutes before I get up, back to 58 until thirty minutes before I get home 10 hours later. Then back down at bedtime. I do the same thing during warmer weather for the AC, but with less swing because I mind the heat more than the cold and because of the humidity in the south. I've noticed with the new furnace that it seems to cycle on and off more until the house heats up and my attempts to be frugal end up costing more! Should I up the thermostat settings when I'm gone? Thanks, bailey
 
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Old 01-01-09, 10:02 AM
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What worked for me

You will probably get some varied opinions on this question, but I will share my thoughts on this subject and then let others chime in as they see fit.

I have a two story house, and when we first moved in I noticed that our gas furnace would run almost constantly during cold weather. In the morning when I had the thermostat set to bump up to 68, it would cycle on, run for 10 minutes, cycle off for about 5 minutes, and then repeat the cycle over and over until the house finally reached the desired temp. It was driving me nuts.

There is a certain amount of inefficiency every time the furnace has to cycle. First, the heat exchanger has to warm up before the blower will kick in and start circulating air through the house (lost energy). Second, once the burners turn off, the blower continues to run for a period of time and then shuts off, usually leaving the heat exchanger still warm, but not hot enough to have the blower run (again, lost energy). If you can reduce the number of cycles, and yet still accomplish your goal of heating your house evenly, you will have saved energy and more imortantly, money.

What I failed to mention earlier was that while my furnace was cycling and driving me nuts, my downstairs was still cold, but my upstairs was becoming suffocatingly hot (my thermostat is located downstairs). I did two things to help alleviate this problem. First, I adjusted the swing on my thermostat up slightly to allow for slightly higher swings in temperature before the furnace cycles on and off. In my case, I set my swing to 5 instead of the default 3. This setting will vary depending on what kind of tstat you have. On mine, a setting of 3 was equivalent to about a 1 degree swing in temp from the desired setting. So, the furnace would turn on at 67, and off at 69. With a swing of 5, it now turns on at about 66.5 and off at about 69.5 (with the tstat set to 68). This may sound like a lot, but it's really not that noticeable.

Second, durning the winter I close all of my upstairs registers, and open the downstairs register wide open, thus forcing all of the hot air downstairs. Since hot air rises, it all eventually ends back upstairs anyway, but this keeps the temperature differences between upstairs and down to a minimum. With this arrangement, my furnace will now bring my house up to temp in only 2 or 3 cyclings instead of the 15 or 20 it was doing previously. Not only is it more efficient, but I don't have to listen to the blasted furnace turning on and off all the time.

There is one last thing I will suggest, if it is adjustable on your furnace. On some of the newer ones it is not, so you will have to check. If you can adjust the temp for when your blower kicks in and out, you may be able to save a little money as well. Have your blower kick in and out 5 degrees lower than the default setting. In other words, if it normally doesn't kick in until the heat exchanger reaches 110 degrees, have it kick in at 105 or even 100. On the way out, if it normally shuts off at 90, let it run until it reaches 85. Again, you've already spent the money to warm up the heat exchanger, you might as well milk all the warm air you can out of it. And 85 is still warmer than the 67 you're trying to get your house up to!

Hope this helps, good luck!
 
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Old 01-02-09, 05:22 AM
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1) Longer run times are more efficient.
2) If you are on a gas furnace, the more setback (less the furnace runs) the more $$$ you save.

3) setbacks should promote longer run times when trying to recover from colder set points. Why are you seeing short run times?
 
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Old 01-02-09, 05:39 PM
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Originally Posted by bailey550 View Post
I have a new Trane variable speed gas furnace and live in Atlanta, GA area.
What did you get for t-stat? (Make and model)

I set the thermostat down to 58 at night and when I'm gone during the day, then up to 67 thirty minutes before I get up, back to 58 until thirty minutes before I get home 10 hours later. Then back down at bedtime. I do the same thing during warmer weather for the AC, but with less swing because I mind the heat more than the cold and because of the humidity in the south.
My settings are close to what you do.

I drop mine down to 60 at night, 68 when awake/home and 55 in the day time I am not home, and I think I am saving on gas.


I've noticed with the new furnace that it seems to cycle on and off more until the house heats up and my attempts to be frugal end up costing more! Should I up the thermostat settings when I'm gone? Thanks, bailey
It shouldn't be cycling like that.. it should run non stop till the set point has been met... Sounds like it's tripping on high limt, and or the t-stat is slowly bring the temp in in recovery.

I"ll wait and see what you got for t-stat on the furnace.
 
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Old 01-02-09, 05:53 PM
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Originally Posted by kaman View Post
In the morning when I had the thermostat set to bump up to 68, it would cycle on, run for 10 minutes, cycle off for about 5 minutes, and then repeat the cycle over and over until the house finally reached the desired temp. It was driving me nuts.
As in my last reply on the OP question, the furance should be running steady till set point.. Sounds like it was over heating or something.


With a swing of 5, it now turns on at about 66.5 and off at about 69.5 (with the tstat set to 68). This may sound like a lot, but it's really not that noticeable.
In your mild winters, you may be able to get buy with that, but here in Minnesota, people would be crying.. I used to have a "Swing" model t-stat that did the on at 67 and off at 69, and I could feel the the swing and I no longer have that stat and updated to the Honeywell that cycles the furnace as needed to keep the steady temps.. (Cycles about 3 times an hour)

There is one last thing I will suggest, if it is adjustable on your furnace. On some of the newer ones it is not, so you will have to check. If you can adjust the temp for when your blower kicks in and out,
New furance don't do that anymore.. it's timed on and off.
 
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