Leave AC on or off all day? (small apartment)

[oneofusjustin]

So, its hot this summer we all know that, and we all know the age old saying about leaving your AC on at a slightly higher temp while you are at work all day is better on your electric bill than trying to make it play catch up once you get home.

I believe this theory maybe correct in large homes/buildings, especially when it comes to heating. However, i do not believe it is true for AC in the small apartments that most of us live in (after moms basement).

My experience with standard 1 or 2 bedroom apartments is this. Turn it off all day and close your blinds, when you get home it takes a MAX of 15 mins to make it comfortable, and the AC isn't running nearly as hard as it would during the day because the air temp around the compressor is much cooler at night.

I think people are wrong in the whole " well it has to work harder when your apt is hotter" idea. its a machine, it dosent know how much work it has to do you set it to 70 it blows at 70, it may work longer, but not harder

what are your experiences with your small apartment?

 

[Wyndru]

In my experience a window unit (or single source AC) is better off during the day, but a central AC is better to leave on at a higher temp.

 

[Murloc]

I think that if you behave correctly (which means: close EXTERNAL blinds and windows during the day, open only at night when the temp is comfortable), you don't need to leave AC on all day, unless you have a big house and central cooling which is wasteful but I understand that energy cost is very low in the US.
If you have central AC it probably won't waste too much energy if you set it at 28°C and seal the house from sunlight and air from outside.

 

[SlitheryDee]

I used to turn mine completely off in the day. I since I got a cat, I just set the thermostat to go to 85 degrees when I'm at work, and back to 68 when I'm home. I was kind of surprised when my electric bill didn't change much at all. Maybe there's something to that theory after all.

 

[johnjohn320]

http://www.rodale.com/efficient-air-conditioner-use?page=0,1

 

[Theb]

It's a myth that leaving the AC on while you're away at work uses less energy than turning it on when you get home. Here's why:

Heat goes to where it's not. That's why heat from outside goes into your cooler home. With the AC off, at some point your house will be so hot it can't absorb any more heat. When you come home and turn the AC on, the AC removes all that heat.

But if the AC is on when you're gone, then you've turned your house into a heat magnet. But keeping it artificially cool, there's no limit to the amount of heat it can absorb. It can always absorb more heat. And your AC has to remove that heat constantly. Your AC kicks in and removes some of that heat, then the house is cooler so it sucks in more heat from outside, so your AC kicks in again and removes that heat, and so on.

This means that throughout the day, your house has absorbed way more than one houseful of heat. And your AC had to remove it all. By contrast, with the AC off all day, then it has to remove just one houseful of heat when you come home and turn it on.

Let's say you leave the AC off, and your house absorbs 20k BTU's of heat and then stops, because that's all it can absorb.

Now let's say that you have the AC running instead. The house absorbs 5k BTU's of heat, so the AC kicks in and removes it. Then it absorbs another 5k BTU's, and your AC kicks in and removes that. Repeat that process several times during the day.

The actual numbers will vary, and I haven't tested this to see exactly how much the penalty for leaving the AC on during the day is, but there is zero question that running the AC all the time uses more energy than turning it on when you get home. This is not a gray area, it's simple physics, and no person with any knowledge of this subject disputes it. Running the AC when you're not home wastes energy, period.

http://michaelbluejay.com/electricity/cooling.html

 

[FoBoT]

28 degrees Celsius = 82.4 degrees Fahrenheit, way way too hot for a dwelling

i quit doing all that crap
all year long, if i get a little cold, i bump the thermostat a little. if i get a little warm, i bump the thermostat a little. i quit paying attention to the temperature and the numbers on the thermostat

 

[gorcorps]

I'm in a small apt and I barely touch the thermostat. Electric bill changes by 10 bucks at the most. Worth it to come home to a proper temp already.

If I had a fancy thermostat I would program it, but I don't so I just leave it on.

 

[CraKaJaX]

I turned my AC on during lunch yesterday. The next couple days in NY are supposed to be brutal. I don't plan on shutting it off until tomorrow night/Friday morning when the temp goes back below 90 degrees. I'm in an apt with one unit cooling the entire place.

 

[mmntech]

My house never seems to get that uncomfortable during the day. Mostly at night for some reason. Probably has to do with me using the computer in the evening, which heats up my bedroom. I prefer to run it at night so I sleep better. Electricity is cheaper at night too.

 

[trmiv]

I leave mine on, but turned up. But I have dogs, a cat and a reef aquarium at home. If I didn't keep the AC down I'd need a chiller for the aquarium, so I'd be spending money cooling something. Also it gets hotter than the devil's balls here in NC in the summer, so leaving it off would really suck.

 

[iRONic]

I think that if you behave correctly (which means: close EXTERNAL blinds and windows during the day, open only at night when the temp is comfortable), you don't need to leave AC on all day, unless you have a big house and central cooling which is wasteful but I understand that energy cost is very low in the US.
If you have central AC it probably won't waste too much energy if you set it at 28°C and seal the house from sunlight and air from outside.

Not here in CT! I practice all of those behaviors and then some.

We're currently at 91° F -- 51% Humidity -- Heat Index of 104° F.

 

[GagHalfrunt]

Off. With small rooms it doesn't take long to go from 95* to comfy. Your A/C won't be playing "catch-up", it's going to get the job done in 15 minutes.

 

[HydroSqueegee]

dont be a pussy. when i lived in my first apartment i didnt turn on my ac until the internal temp was pushing the mid 90's. I remember fondly my time sitting in front of my PC sweating my balls off while playing Ultima Online.

I kinda miss my first house. it was built in '49, cape cod style. lots of nice large windows and made to open them up and let the breeze blow through. Breezy days in the mid 80's were no problem. house stayed comfortable. Days with no wind required fans in the windows but was tolerable. But after a while the window AC's had to be put in because late July/August in south west Ohio sucks balls.

the new house (built in the 50's) has central AC thank god. hardly any widows and small ones at that. i really need to put in insulation too. So it sits at 74 most of the time all day every day once it hits 80 outside.

 

[MixMasterTang]

A/C also "Conditions" the air (removing humidity), so this will probably play a factor in people's comfort levels and the ability to leave the A/C at a higher temp or completely off. I have a rather large house that would make hours to cool down if it got too hot, so I leave the thermostat at 76 during the day and down to 70 from 10pm-6am. I have noticed that even when it is only ~80 outside but high humidity coming inside to a non humid 76 degrees feels like a much much larger change in temp then only 4 or 5 degrees.

 

[Dallascisco]

Use a programmable thermostat to adjust the temps differently while you are home and when you are away. We have it set to 75 when we are home and 82 when we are at work.

 

[Brainonska511]

So, its hot this summer we all know that, and we all know the age old saying about leaving your AC on at a slightly higher temp while you are at work all day is better on your electric bill than trying to make it play catch up once you get home.

Why doesn't this myth die? It is easier on your electric bill to turn it off while you're not home. Laws of Thermodynamics and such.

 

[lupi]

Yeah sorry, aaint turning the AC off so my 95f heat sink will be waiting for when I get home.

 

[Wyndru]

I've always thought it has to do with how long you are not home during the day, as well as how insulated your house is. Below is an example of the argument I hear most present concerning this, I've never tested it since we have animals and need to keep it somewhat comfortable for them.

If your house gets up to 85 during the day and it takes 2 hours of full run time to get it back down to 70, wouldn't that be just as wasteful than just letting it kick on and off occasionally throughout the day and maintain the temp? If on an average summer day, the AC only kicks on for about 10-15 minutes an hour and maintains the temp, and you are gone for 8 hours, that would be 80-120 minutes of AC throughout the day, and the temp will already be comfortable when you arrive home.

I don't know about the 10-15minutes an hour though, I think ours runs more than that each hour so this could be way off. I'm simply posting this as it's how I hear most people support this idea. I do know that our central air does take quite a while to get it from 85 to 70 though, so the 2 hours I used is not an exaggeration.

 

[Brainonska511]

I've always thought it has to do with how long you are not home during the day, as well as how insulated your house is. Below is an example of the argument I hear most present concerning this, I've never tested it since we have animals and need to keep it somewhat comfortable for them.

If your house gets up to 85 during the day and it takes 2 hours of full run time to get it back down to 70, wouldn't that be just as wasteful than just letting it kick on and off occasionally throughout the day and maintain the temp? If on an average summer day, the AC only kicks on for about 10-15 minutes an hour and maintains the temp, and you are gone for 8 hours, that would be 80-120 minutes of AC throughout the day, and the temp will already be comfortable when you arrive home.

I don't know about the 10-15minutes an hour though, I think ours runs more than that each hour so this could be way off. I'm simply posting this as it's how I hear most people support this idea. I do know that our central air does take quite a while to get it from 85 to 70 though, so the 2 hours I used is not an exaggeration.

Except that example is perfectly wrong. Maintaining the temperature means keeping a larger temperature differential between inside and outside, and heat flows from hot to cold, so you're spending more energy maintaining that gradient. Allowing your house to warm while not there means there is a lower temperature gradient between the outside and inside, so the warming would slow down and you're not wasting energy. It takes less energy to lower the air back down to the desired temperature than it does to maintain that differential between inside and outside. If you want it cool when you get home, use a timer.

 

[Wyndru]

If you want it cool when you get home, use a timer.

This is the part I'm confused about though. If it takes 2 hours of constant AC to bring it back down from the warmth built up throughout the day and you get home at 5, wouldn't it have to kick on at 3 and basically be working nonstop for 2 hours during the (possibly) hottest part of the day to get it back down to your comfort level?

Is that less wasteful than just letting the AC maintain during the cooler part of the day (morning to 3) and not having to struggle to drop those degrees later on when it's hotter outside?

 

[BurnItDwn]

My house is insulated pretty well, and my AC is 25 years old and only seems to cool the house down by a small amount ...

It takes the AC like 1 hour per degree to lower the temperature. I leave it on all day.

 

[nageov3t]

Off. With small rooms it doesn't take long to go from 95* to comfy. Your A/C won't be playing "catch-up", it's going to get the job done in 15 minutes.

+1

my apartment isn't necessarily small, but the rooms are, for the most part (my kitchen and living room are pretty big, but I generally don't bother cooling those rooms unless I've got company).

my home office and bedroom, which is where I spend most of my time during the summer, are small and only take like 10-15 minutes to cool with my window unit on low or medium

 

[Chiropteran]

I have pets so I keep it on all the time. It doesn't cost much, advantage to having a small condo I guess.

 

[ShawnD1]

So, its hot this summer we all know that, and we all know the age old saying about leaving your AC on at a slightly higher temp while you are at work all day is better on your electric bill than trying to make it play catch up once you get home.

What meth head told you that? That's like saying you should leave your car idling overnight so it doesn't need to warm up in the morning. Absolutely retarded. Try applying this logic to any other thing in the world. Suppose I want to have hot tea in 1 hour. Does it make sense to wait 1 hour then boil the water, or should I boil the water right now and try to keep it almost boiling the next hour?