Most Energy Efficient program for thermostat

[brianthiede]

I have a gas furnace and a programmable thermostat. What is the most energy efficient way to set it up during the day when nobody is home

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A) Set it to a very low temp (but warm enough to keep pipes warm) so it is essentially off until it kicks on with enough time to bring the house up to a comfortable temp before we get home in the evening

B) Set it somewhat below the comfortable temp, but not so low that the system needs to work real hard for a while to bring it back up to the set temp

My instincts say A - that way the only energy used goes to heating up the house for when people will be there. But I'm not sure if for some reason it would use more energy heating up like 20=B0 at the end of the day as opposed to hovering 10=B0 or so below the set temp, then warming up the last 10 at the end of the day. If it matters, I live in Virginia and the house is unoccupied for about 9 hours during the day.

[Travis Jordan]

By the way, the concept of "working hard" is unknown in terms of furnace energy usage.

[James]

You are correct in suspecting that there is a point at which it will cost more to return the house to the desired temp than it would have cost to maintain a intermediate temp. No one can really tell you what that point is though as the size and efficiency of the furnace and the house insulation also are factors. With only 9 hours to work with I suspect you will not loose much heat. Leave it off one weekend day when you are home and it is cold out. See how much it drops inside the hour each hour Then you can see how long it takes to bring it back to the desired temp. If you really want to get serious get something that will measure how many minutes a day the furnace runs and then you can experiment to see what effect various strategies have on the total daily run time on similar days. A resetable hour meter from a boat and a motorcycle battery charger hooked to the furnace fan power will do.

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A) Set it to a very low temp (but warm enough to keep pipes warm) so it is essentially off until it kicks on with enough time to bring the house up to a comfortable temp before we get home in the evening

B) Set it somewhat below the comfortable temp, but not so low that the system needs to work real hard for a while to bring it back up to the set temp

My instincts say A - that way the only energy used goes to heating up the house for when people will be there. But I'm not sure if for some reason it would use more energy heating up like 20° at the end of the day as opposed to hovering 10° or so below the set temp, then warming up the last 10 at the end of the day. If it matters, I live in Virginia and the house is unoccupied for about 9 hours during the day.

[Power's Mechanical]

They say 10F setback. How about you try it both ways and report back in two months.

[Jeffrey Lebowski]

Appreciate please explain further the above...

[Travis Jordan]

Citation please?

[Travis Jordan]

Citation for your reading pleasure:

" A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. This misconception has been dispelled by years of research and numerous studies. The fuel required to reheat a building to a comfortable temperature is roughly equal to the fuel saved as the building drops to the lower temperature. You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed. So, the longer your house remains at the lower temperature, the more energy you save."

[Jeffrey Lebowski]

Place where it get's tricky though is when you have a heat pump running as primary but calling in aux strip heating ( or even fossil, depending on current energy pricing structure ) to effect rapid recovery...this is esp true where the setback was of relatively short duration.

[Anonymous]

Well I think outside temperature is the biggest factor with setbacks. I agree the money you save during the initial setback to low heat is roughly what it will cost to reheat to high heat, but I disagree a little when they mention savings throughout the following 8 hrs of setback. Sure the house is down to 15c but it now runs to maintain 15c, the same way it woul run to maintain 20c. So where's the savings? Your initial setback savings are spent reheating back to high temp.

"You save fuel between the time that the temperature stabilizes at the lower level and the next time heat is needed."

If it's -15c outside I don't think there would be much of an off period and therefore not much savings. I would like to see these "studies" that website mentions.

Am I missing something here?

-Canadian Heat

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[Jeffrey Lebowski]

By your reasoning, better to leave the kitchen stove going and set to 350 deg all the time then....

[Bubba]

Exactly why you are so clueless

Thus the reason you aren't the brightest bulb in the bunch.

Oh my, a genius! You didnt hurt your brain on that one did you, Canuck?

It wouldnt do any good. It would be way over your head. Stick to "Dick and Jane" books. Lots of pictures.

Just a brain. Canucks dont come with them. Its an option. You couldnt afford it on your $100 a day plus beer. Bubba

[CJT]

Delta temperature affects heat loss.

[Travis Jordan]

True. I didn't bother to mention this since the OP was only asking about his furnace.

[Jeffrey Lebowski]

Fair enough then.

[Anonymous]

Sorry bubba, your post makes no sense. Clearly you have no technical skill. Way to recite what I typed, without offering any new info. Typical useless post by bubba! I'm suprised your white trash family can afford the bandwidth...o that's right no net at the trailer park. HAHA

+4 DANgER

-Canadian Heat

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[Bubba]

I think you need some new material. While your at it your spelling seems to be getting worse. Forget the spellchecker? Still cant seem to get the hang of posting can you. You post as if you are talking to yourself. I think you are. You are a fat ass loser and a Canuck at that. Life must suck to be you. Bubba

[Bob_Loblaw]

Bubba wrote

Ummmm.....nothing wrong with being a canuck.....

[Bubba]

Certain ones, Not you Bob. Bubba

[Stormin Mormon]

The fuel used depends on the heat loss. Colder building = less heat loss.

[Stormin Mormon]

The savings is that a 15c house loses less BTU than a 20c house.

1) The heat difference is lower, so the heat pushing through the walls and ceiling is slower BTU per hour 2) the air loss through convetion is cooler air