Turning down the A/C??

[disneymom3]

So, if you were going to be gone for 4 days and the temps were supposed to be near record highs while you were gone, how far would you turn the thermostat up? When we are home we keep it from 72-75. I turned it to 80, but I have heard that if you do it too high, the energy it would take to cool it back down negates your savings. Is 80 good?

 

[golfgal]

I would turn it to 80 or so. If you keep your shade/blinds closed it won't get that warm in there while you are gone so cooling it back down won't be a huge issue. This is assuming you have some insulation in your home.

 

[Towncrier]

We turn our A/C off when we leave home for vacation. My opinion is that it won't cost anymore to cool the house back down when you return. It doesn't take any more energy to cool the house down from 80 to 70 than it does to maintain the house at 70 while you are gone. As long as you don't let any extra moisture into the house while you are gone.

You realize, of course, that people will disagree with my statements and that you have opened Pandora's box.

I'm going to go get my box of popcorn and wait for the replies.

 

[mamacatnv]

I do 80 when we leave for a week every summer, mainly because our cats are in the house. Although it takes sustained heat to get my house over about 75-78, it is well insulated, we keep the blinds closed and the main areas don't get afternoon sun.

A few years ago we went to DL in November. We turned the heat off, because we are stupid and we usually don't have severe cold snaps in Nov. Well, while we were gone we got a huge snow storm. When we returned our house was 45 degrees, it was 10 at night and the cats were buried under the down comforters. We could see our breath in the house!

Now I use an automated thermostat which we set at 80 for summer departures and 60 for winter.

 

[disneymom3]

We turn our A/C off when we leave home for vacation. My opinion is that it won't cost anymore to cool the house back down when you return. It doesn't take any more energy to cool the house down from 80 to 70 than it does to maintain the house at 70 while you are gone. As long as you don't let any extra moisture into the house while you are gone.

You realize, of course, that people will disagree with my statements and that you have opened Pandora's box.

I'm going to go get my box of popcorn and wait for the replies.

Really??? Only on the DIS could A/C be considered controversial! Thanks for the advice. Maybe I better not say what I have decided to do. The humidity is an issue though so I am leaning toward not turning it all the way off.

 

[disneysteve]

I have heard that if you do it too high, the energy it would take to cool it back down negates your savings.

This is absolutely incorrect, one of those urban legends. If you want proof, I'll dig it up as we've had this discussion in the past.

Any time your AC is not running, you are saving energy. So the higher you set the temp, the less it has to run to maintain that setting. If you set it at 70 and it is 90 outside, it has to run very frequently in small bursts to hold that temp. If you set it at 85, however, it hardly has to run at all.

We put ours at 80 because we have an aquarium and I don't want it getting any warmer than that in the house. If not for the fish, I'd probably do 85.

 

[CEDmom]

I think 78-80 is fine. I'd be reluctant to turn it off because of the humidity factor. It could take quite a bit of time to get the house comfortable enough to live in.

 

[Towncrier]

This is absolutely incorrect, one of those urban legends. If you want proof, I'll dig it up as we've had this discussion in the past.

Thanks for the explanation Steve. It's good to see that the laws of thermodynamics are observed here on the CB.

 

[mickeyfan2]

This is absolutely incorrect, one of those urban legends. If you want proof, I'll dig it up as we've had this discussion in the past.

Any time your AC is not running, you are saving energy. So the higher you set the temp, the less it has to run to maintain that setting. If you set it at 70 and it is 90 outside, it has to run very frequently in small bursts to hold that temp. If you set it at 85, however, it hardly has to run at all.

We put ours at 80 because we have an aquarium and I don't want it getting any warmer than that in the house. If not for the fish, I'd probably do 85.

Steve is SO right. We set our to 78. Our home is extremely energy efficient and so is our system. We keep ours at 70 all other times. The big reason to not turn it off is the humidity. Wood furniture, floors and cabinets do not like to see huge swings in % of humidity, also mold can and will grow if the humidity in the home is >50%. We keep our house humidity at 50% from spring to fall. Wood furniture will swell and shrink too quickly and may crack or buckle.

 

[puffkin]

We have a programmable thermostat, so we have it set to go to 80 during the day while we are at work. When we go away on vacation we set it at 80 for the whole week. I have a cat and dog though, so I don't like to go any higher. Plus with the humidity, our doors swell and really stick so we don't go above 80.

 

[SC Minnie]

We bump ours up to around 80 when we go away for a week in the hot months. One year DH turned the A/C completely off when we went on vacation in June. We get home about 8pm and it is 95 degrees in the house-felt like an oven. It took well into the middle of the night to get even remotely comfortable. We will never turn it off completely when it is going to be hot outside.

 

[azgal81]

I turn it off completely when I go on vacation it doesn't take that long to cool the house back down when I return.

 

[Buckalew11]

Gosh, ours is set at 78 all the time unless I'm cooking something in the oven then I drop it down to about 76. I would think it would be fine on 80.

 

[Magickndm]

Mine is set at 80 right now and I'm home! If I had it any colder it would never shut off.
When we go away we set it at 84, it's not good for electronics or furniture to get too hot.
We also turn off our water, even if we're just gone over night. My dad is in the insurance business and it seems washers and pipes like to break while no one's around.

 

[Mishetta]

Oh my goodness ~ I must be too hot blooded because I have to keep mine anywhere from 70 to 72. Today I know I'll have the oven on, so I'll probably turn it back down to 70! I want to be comfy in my home. Anything over 75 is not comfy for me. Of course, the deeper I get into my 40's, the colder I like it so.....

I also believed that you should keep your settings the same all the time because it would take a lot of energy to re-cool the house. I'm curious so I'd like to read where you obtained your information disneysteve. It's always best to be informed.

I do remember when my dear Mom was alive, we'd play with the thermostat game all day long. I'd make it cooler, she'd crank it up to 80, I'd go back to 72 & she'd sneak it back up to 80. Our bill was higher than normal. Now that I keep it at 70 - 72 all the time, our electric bill was $170 for the month. It's been extremely hot this month too & that was our highest bill so far.

Off topic but our friends in CA (Diamond Bar area) called yesterday & were telling us about their electric bill being $429 for this month & they keep their A/C at 86! They live in an 1800 sq ft ranch. We're in a 2500 sq ft colonial. Energy cost must be much higher in CA than here in MI! Mama Mia!

 

[luvwinnie]

So, if you were going to be gone for 4 days and the temps were supposed to be near record highs while you were gone, how far would you turn the thermostat up? When we are home we keep it from 72-75. I turned it to 80, but I have heard that if you do it too high, the energy it would take to cool it back down negates your savings. Is 80 good?

If NO ONE is going to be there, I'd turn it off. I don't like leaving anything electrical on.

 

[budbeerlady]

I have this argument weekly with the mother in law. Usually it is about heating but here is what I show her... http://www.consumersenergy.com/apps/pdf/more-100-ways-save-on-bill3.pdf Page 8-9 on the bottam left, set the temp higher when you are gone.

She also argues that keeping it cool (like 75) round the clock (or hot like 78) costs less. As far as the heating I know she used almost double the propane I did, so I am sticking with my theory about changing the temps at night and when you leave.

 

[Towncrier]

And air conditioner is in the most simple terms a heat transfer device (or heat pump). It takes a certain amount of electricity per BTU of heat transferred. It doesn't matter to the heat pump (A/C) whether you are transferring heat from a 95 degree home or a 75 degree home. You are simply using the electricity to transfer heat from inside your home to outside. Turning the thermostat down to 65 doesn't make the house cool down any faster (much like turning the heat up to 95 doesn't make it heat up faster).

When it is hotter outside than inside your home, heat is transferred (free of charge) from outside to inside until both reach the same temperature. You have to put energy into your A/C in order to reverse this effect. The amount of thermal mass (or stuff you have in your home) does effect how long it takes for this balancing act to occur. If you have lots of furniture, it will take more BTUs to heat up your house. You have to realize that it also took the same number of BTUs to cool off that furniture and stuff in the first place. In other words, the effect cancels out. I think that this is biggest source of confusion. When I was growing up (before engineering school), I too was also told to leave the thermostat alone because you didn't want to let all that stuff heat up. The only disadvantage to letting your stuff get warm is that it will take longer to cool it all back down again. But remember that it took longer for it to heat up as well. BTUs in equal BTUs out.

So if you leave your thermostat set at a fixed temperature, it will have to work to maintain the status quo (or the difference between indoor and outdoor temperature). As the outside world attempts to heat your home, you use electricity to balance out the heating effect.

By turning off the A/C, you stop fighting the battle to maintain status quo. Your house will heat up (and cool down) as the outside temperature rises and falls. And it won't cost you anything to allow that to happen.

When you turn the A/C back on, it will transfer BTUs out of your home until the status quo is once again established. Herein lies another difficulty. If it is gosh awful hot outside when you attempt this, and if your A/C is sized correctly, it might not be possible for your A/C to drop the temperature inside your home as quickly as you would like. But it is not taking any more energy to transfer those BTUs than it would have if you had left the A/C on all the time.

What I am trying to describe is entropy, the effect that tries to bring everything in the universe into balance. Given enough time, everything in the universe will eventually reach equilibrium. There's no way around it (in the very long term).

Last winter, there was a similar thread on the DIS about heating your home in the winter. Since heating and cooling are actually the same (just swap inside and outside in my previous descriptions), the analogy holds.

Think of your home as a pan of water on the stove. Which takes more energy?
A. Leave the pan of water simmering so that you can easily bring it to a boil by simply turning up the burner slightly.
B. Leave the burner off until you want to boil the water.

Although answer A would provide you with nearly instant boiling water, the cost to keep the stove turned on day and night to keep the water warm is obviously more than case B.

So keeping your house at a constant indoor temperature is going to cost more than to let the house warm up while you are out. But you'll have to explain that to my wife when she arrives home this evening to the little note that I left on the kitchen counter explaining that I turned off the A/C when I left home this morning because nobody was going to be home. My little part to reduce global warming.

 

[Rock'n Robin]

Boy TC, if you were my DH and you turned the air off I'd be kicking your behind, global warning be darned. I work in a HS without A/C, and in those late August days I look forward to walking into my air conditioned home--even though I only set it at 78. If I left one sweatbox to come into another one---I'd be out for bear.
As for vacation, I can remember when we went away to DH's sister's wedding years ago. We then lived in a house without A/C. It was a cool summer and we didn't think about it--can't leave windows open when you're gone anyhow. But it turned out to be the hottest weekend of the summer here in NW Ohio (while we were in Rochester NY) and when we came home it was about 92 upstairs! The cats would not leave the basement! If we would have had fish they would have been boiling! DD#1 was 5 months old, we had DH's cousin and grandmother with us, and we all had to sleep downstairs! So when we go on vacation now we leave the A/C on 80 to keep the house tolerable to us when we return, and to our 2 cats.
Robin M.

 

[Tantor]

I think 78-80 is fine. I'd be reluctant to turn it off because of the humidity factor. It could take quite a bit of time to get the house comfortable enough to live in.

this is what we do just to keep the humidity out of the house but usually just a tad higher.