Is it cheaper to keep your A/C on all the time or turn on and off?

[Kies99]

Here's the scenario:

We have a programable A/C. Nobody is home Monday-Friday between 7am and 5pm. Assume we'd have the A/C set to 75 degrees.

Here's the question:

Would it be more cost efficient to have it set to keep a constant temp of 75 degrees all the time, OR would it be better to have it off during the day and come on about an hour before we got home and have it cool the house down to 75?

My thought is that it may run more frequently if we have it set to maintain 75 degrees, but it wouldn't run as long as it wouldn't need to cool down as much. So, which way is more efficient?

 

[canadianmom2three]

Last year I was convinced my AC wasn't working, it would run constantly, all evening, even all night! and not cool the house at all. I went so far as to call in a repair man, who thoroughly checked it out and determined it was working fine. He asked me about what I do during the day, and I replied I had programmed it to go off after we left for work, and come back on just before we got home. During the day, the temp in the house was going up to the high 80's, and then the air conditioner was having to try and cool it back down to mid 70's. He explained that your house gets very hot and humid, and it is not just the air inside the house that gets hot, it is everything, the flooring, the furniture, bedding, drapes etc. all hold in that hot humid air, and the AC just can't cool it that quickly at the end of a hot day. He said it is far better to keep it set to still cool during the day (not super cool, but enough to keep it managable) in order for the AC to be able to keep up. HTH

 

[jax677]

I have always wondered this too. I have always heard it puts a strain on the unit to wait until the house is hot and then turn it on. But I imagine it matters how hot the house is getting.

I have noticed that if I wait until the afternoon to turn my ac on it seems to take along time to cool the house off. Something about radiant heat I think. Or is it that the heat gets trapped in all the furniture and you have to cool that area off too? Sorry I guess I have more questions than answers.

 

[jax677]

Oops, we posted about the same thing at the same time. I guess great minds think alike.

 

[gshumaker]

If you have a programmable thermo and no one is home during the day program it to kick up about 5-6 deg when the last person is leaving the house and then to turn back down to your normal setting about 30 minutes before the first person gets back home. That way you will never even notice the change in the temp but you will notice it on the electric bill.

Also turn off all those ceiling fans when you are not there. They do not lower the temps in the rooms they just make it feel cooler to us when we are in the rooms. That will save you a few extra $$ also.

 

[audrabolster]

I have heard that it is cheaper (and better) energy wise to not run it all day.

 

[sarahkaiserdse]

I own an hvac company. It is not cheaper to turn the unit off. If you are turnng the thermostate up or down a few degrees its not going to make a huge dent one way or the other. But if you turn it way up to say 80 degrees or turn it off the a/c unit has to work much harder to pull all the moisture out of the home. An a/c is basically a giant dehumidifier and when its turned off its starting from scratch and going to run for longer periods of time rather then just short bursts to get the temperture at what the thermostate is set for. But you should also be realistic if the temperture outside is 100 your a/c may never cool your house to 70 of course this varies due to how often do you have your a/c checked, does the a/c tech do a superheat test to check the freon levals if its off just a smidge with to much or to little your unit will not run as well as it could. Have you had the coil cleaned to make sure its not retricted. Don't wait until your unit is not working in the dead of summer to have it checked out. We charge a service call plus labor and parts when its not working, but if you call when its working its a flat fee to clean and check the unit out. Plus when its really hot more units break down and you can't always get same day service.

 

[Jakesmom504]

We were always told to not turn it off completely, just turn it up when you aren't home. For us it doesn't really matter unfortunately since DH and I work opposite hours and we have a bulldog. They can't tolerate heat...our dog and DH! We have a programmable thermo., so I try to keep it up a little bit if we won't be home but not so much that it has to work extra hard to cool the place off when we do get home.

 

[ntsammy5]

I own an hvac company. It is not cheaper to turn the unit off.

Thanks. That makes intuitive sense. That's what I plan on doing from now on.

 

[ajk912]

I own an hvac company. It is not cheaper to turn the unit off. If you are turnng the thermostate up or down a few degrees its not going to make a huge dent one way or the other. But if you turn it way up to say 80 degrees or turn it off the a/c unit has to work much harder to pull all the moisture out of the home. An a/c is basically a giant dehumidifier and when its turned off its starting from scratch and going to run for longer periods of time rather then just short bursts to get the temperture at what the thermostate is set for. But you should also be realistic if the temperture outside is 100 your a/c may never cool your house to 70 of course this varies due to how often do you have your a/c checked, does the a/c tech do a superheat test to check the freon levals if its off just a smidge with to much or to little your unit will not run as well as it could. Have you had the coil cleaned to make sure its not retricted. Don't wait until your unit is not working in the dead of summer to have it checked out. We charge a service call plus labor and parts when its not working, but if you call when its working its a flat fee to clean and check the unit out. Plus when its really hot more units break down and you can't always get same day service.

Thanks for posting, I really appreciate it. I was thinking that we are having record highs in VA right now..100 for the next few days. That's at least 10 degrees higher than our usual average high even for July, so really hot. My A/C has been running nonstop and I in the afternoons I can't get the house lower than 77. This is fine, but I was thinking I should have it checked. But, my DH says since it is cooling the house almost 30 degrees, it's going to be a battle.

 

[Todd&Copper]

According to information ont he DOE website, you should turn off window ac units when you wil be away for a few hours, but raise the temp for central air units.

 

[carymomof3]

I've just been contemplating this subject. We are leaving for DW next Friday. We'll be gone a week. We won't turn off the A/C, but how high should we set it? I was thinkng 80, but now am wondering if that's too high. Keeping in mind, that it's in the high 90s here right now, so it's definitely A/C weather. TIA for any advice.

 

[estherhead]

I own an hvac company. It is not cheaper to turn the unit off. If you are turnng the thermostate up or down a few degrees its not going to make a huge dent one way or the other. But if you turn it way up to say 80 degrees or turn it off the a/c unit has to work much harder to pull all the moisture out of the home. An a/c is basically a giant dehumidifier and when its turned off its starting from scratch and going to run for longer periods of time rather then just short bursts to get the temperture at what the thermostate is set for. But you should also be realistic if the temperture outside is 100 your a/c may never cool your house to 70 of course this varies due to how often do you have your a/c checked, does the a/c tech do a superheat test to check the freon levals if its off just a smidge with to much or to little your unit will not run as well as it could. Have you had the coil cleaned to make sure its not retricted. Don't wait until your unit is not working in the dead of summer to have it checked out. We charge a service call plus labor and parts when its not working, but if you call when its working its a flat fee to clean and check the unit out. Plus when its really hot more units break down and you can't always get same day service.

Ditto, Ditto, Ditto!!! My dad owns an HVAC company (I'm the vice-president & worked there 15 years- since I was 16) and what you say is perfect advice. Advice no one listens to.

It's much cheaper to keep it a constant temperature. Why? Because if the house is cool all the time then the system only kicks on every once in a while, whereas if the house is hot (the walls are hot, the floors are hot, the air is hot) then the AC kicks on & STAYS on for a long time to cool everything back down. So if you want to save money, keep it on constantly, but raise it 3-4 degrees more than you did last year. And if you have a programmable t'stat just raise it 3-4 degrees more than that when you're gone. An hour before you're supposed to come home have it set to lower it those 3-4 degrees.

 

[LadyyRedd]

Ditto, Ditto, Ditto!!! My dad owns an HVAC company (I'm the vice-president & worked there 15 years- since I was 16) and what you say is perfect advice. Advice no one listens to.

It's much cheaper to keep it a constant temperature. Why? Because if the house is cool all the time then the system only kicks on every once in a while, whereas if the house is hot (the walls are hot, the floors are hot, the air is hot) then the AC kicks on & STAYS on for a long time to cool everything back down. So if you want to save money, keep it on constantly, but raise it 3-4 degrees more than you did last year. And if you have a programmable t'stat just raise it 3-4 degrees more than that when you're gone. An hour before you're supposed to come home have it set to lower it those 3-4 degrees.

I listen! This is what I've ALWAYS done.

Kimya

 

[Mickeyorbust]

I've been wondering the same thing as OP....thanks for clarifying. And sorry if this is highjacking but does it help on the electric bill to turn up the thermostat a few degrees at night and then back down in the morning (more specifically while we're asleep)? Or would that also be counterproductive?

 

[puffkin]

We set ours at 74 when we are home and it goes up to 80 when we are away. We also set it at 80 when we are on vacation. We have a dog and cat so we don't let it get much warmer than that.

It doesn't need to run real long to bring it back down to the 74 unless it is REALLY hot outside.

We are flipping ours on for the first time tomorrow since we have 95 degree weather for the weekend. I think I am going to set it at 76 when we are home, 80 away, and 74 for bed time.....I like to be COLD to sleep and it takes awhile for the air to get to the second floor.

 

[windycitymom]

Here's a tip: When you hear that high temps are coming, turn on your AC ahead of time and make sure it works. Don't wait until the day of. Yesterday it was 87 degrees in Chicago and we turned on our air for the first time this year. We found out the AC wasn't working and had to call out a repairman. Luckily, we got someone to come out this morning, but it was a hot night in our house. Usually on the first hot day, alot of people find out their units aren't working and the repairman get so busy you may have to wait a few extra days. Everyone should do an annual clean and check (cost $89 here), which I'm guilty of not always doing. The AC is working now, but I should have been more proactive.

 

[mdrob214]

I've been wondering the same thing as OP....thanks for clarifying. And sorry if this is highjacking but does it help on the electric bill to turn up the thermostat a few degrees at night and then back down in the morning (more specifically while we're asleep)? Or would that also be counterproductive?

See, I must be different. I can handle the house at 76-78 or so during the day. I wait until after dark to drop it--overnight it goes down to 74. I like it cooler when I am sleeping! I also don't think I could handle staying inside in 70 degrees in my summer clothes--I'd freeze! We are in and out all day during the summer since I am a SAHM (who rarely stays at home!)

 

[dkdaisy]

OMG, I am so jealous of all of you. I would love to set my AC at 74 and worry about whether that was too low! My DH is contantanly changing to to be set at 67. At 67, with the fan on, I FREEZE. I change it when I can, but he always complains and changes it back. I would love to keep it set at 74 and then up it to 80 or whatever when we're not home!

 

[jrmo]

Okay, with all due respect, this is the budget board! Who is keeping their a/c in the low 70's? If you want to save money, stop turning it up and down and just keep it at at least 78. Ours stays at 79-80, and I find that very comfortable with the lack of humidity. The point of air conditioning is to make the heat comfortable, not be able to hang meat in your house (as my grandfather would say! ) In this day and age, we all have to be conscious of how we use energy, and this is one of those places we all must consider and cut back.