Set Back Thermostats

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billw
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Post by billw » Fri. Oct. 17, 2008 2:19 pm

Has anyone seen a definitive study on whether these things actually save money? I'm changing temps in my downstairs four times a day during the week. I bump it to 70 at 6AM, back down to 65 at 7:30 AM, up again at 4 PM to 70 and back to 65 at 9:00 PM. Weekends it only gets changed twice. I personally think I'm wasting a shitload of fuel doing this. I've seen govt recommendations to set thermostats back but I guess I'm just doubting the amount of times I'm changing temps during the week.

 
Mark (PA)
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Post by Mark (PA) » Fri. Oct. 17, 2008 3:21 pm

Here is a study from our friends up north... or so the article says!

**Broken Link(s) Removed**

 
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Post by Pa Dealer » Fri. Oct. 17, 2008 3:28 pm

Well you doin it right by setting in back only 5 degrees. Some people set theirs back 10 degrees or more and it seems to use more fuel to bring it back up to temp. In bitter cold temps. especially when its windy its a big mistake to turn the thermastat 10 degrees or more since cuiculating cycle times are to far apart, and heat pipes in walls or drafty crawl spaces can freeze.

 
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Freddy
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Post by Freddy » Fri. Oct. 17, 2008 3:29 pm

You're not wasting fuel. They can & do save some fuel.


 
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Post by Pa Dealer » Fri. Oct. 17, 2008 3:32 pm

O yea like Freddy said they do save fuel :lol:

 
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Post by xackley » Fri. Oct. 17, 2008 3:42 pm

I use a set back. 69* at 11 pm, 70* at 4 pm.

But I experimented quite a lot last year. Fact or not, with coal, changes of more that 2* feels like it uses a lot more coal.

In the olden days of fuel oil, I would run 68* during the day, 64 at night. That may or may not have saved fuel. I never counted the minutes the furnace ran while I was asleep, nor the minutes it ran to gain that 4*.

And in the olden days of fuel oil, the floors walls and furniture always felt cold in the winter. There is more to heat than just the air to make a home comfortable.

 
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Mike Wilson
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Post by Mike Wilson » Fri. Oct. 17, 2008 4:30 pm

Interesting... the US Department of Energy recommends setting temperatures back at least 8 F degrees. The Canadian government states that the greatest savings are acheived with setbacks of 6 C or more... which converts to 10.8 F.

Here's some reading:

http://www.energystar.gov/index.cfm?c=thermostats ... hermostats

http://apps1.eere.energy.gov/consumer/your_home/s ... opic=12720

http://www.cmhc-schl.gc.ca/en/co/maho/enefcosa/en ... sa_004.cfm

http://www.energy.ca.gov/releases/1999_releases/f ... re-08.html

 
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billw
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Post by billw » Fri. Oct. 17, 2008 4:38 pm

But I experimented quite a lot last year. Fact or not, with coal, changes of more that 2* feels like it uses a lot more coal.
That's what I thought this morning. It just seemed to take a long time to warm up. I never really paid much attention to the oil unit.


 
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Post by xackley » Fri. Oct. 17, 2008 6:27 pm

quote from second link in mikes' post

"For steam heating and radiant floor heating systems, the problem is their slow response time: both types of systems may have a response time of several hours. This leads some people to suggest that setback is inappropriate for these systems."

Coal would be included in that category. Takes too much time, and coal, burning full tilt, unless you are asleep or gone most of the day and night. A set back might save coal if you only need 8 or less warm hours in a day.

 
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Post by LsFarm » Fri. Oct. 17, 2008 6:40 pm

It's going to depend on the system.. I think it is a waste to heat a room to 70* when no one is there to use and enjoy the heat,, I set my heat back to 60* when the rooms or house are not occupied.. it only takes 20 minutes to warm my rooms from 60* to 70*..

Every heat system is different.. mine is hot water baseboard for the most part,, some is floor radiant.. for a hot air system with a bed type stoker furnace, it may take over an hour to raise the temp 10*, but with my AA boiler always hot, it is a negligable amount of time to warm up a room..

Greg L

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Post by rberq » Fri. Oct. 17, 2008 7:31 pm

billw wrote:I bump it to 70 at 6AM, back down to 65 at 7:30 AM, up again at 4 PM to 70 and back to 65 at 9:00 PM
Interesting, you need the heat a mere 6.5 out of 24 hours. I'm guessing that it is really only about 5 hours out of 24, because you probably ramp it up 30 to 45 minutes early so it will already be warm when you get up and when you come home from work.

It certainly makes sense that letting the temperature drop the rest of the time will save you money, because conduction and radiation to the outside will be less at lower temperature differentials. But 65 vs. 70 degrees is not a very big difference. How about letting it drop to 60 at night -- we find that to be comfortable for sleeping. And during the day, why not let it drop to 50 when nobody is home? The cautions here would be, as others mentioned, the spots where pipes might freeze during the long cycle off-time when the room temperature is dropping. Or as in my house, that one cold spot near an outside wall, under the dishwasher, that is 20 degrees lower than the rest of the room!

What truly seems wasteful in your case, is the fuel used to hike the temp for a mere hour or so at 6AM. Just tell the wife and kids to tough it out for that short time. Remind them how you walked to school in blizzards when you were a kid, three miles in each direction and uphill both ways. Make sure you have a good divorce lawyer lined up.

P.S. Maybe you could wire a cheap electric clock in parallel with your circulator pump(s), so you could measure run time under different setback conditions.

 
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Post by Mike Wilson » Fri. Oct. 17, 2008 8:22 pm

One thing all the documents mention on this topic is that setting the temperatures back too far can result in moisture & humidity issues, as the cooler air is incapable of maintaining the vapor loading, and it condenses out on cooler surfaces, such as windows.

-- MW

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