Should I turn off my AC during the day?

[overdog]

I have always wondered which saves more electricity:

Turning off the AC during the day (jacking it up to 90 F)and running for a few hours straight after I get home from work.

or

Leave the AC at about 80 F and have it come on intermittently while I am away.

By the way the temperature outside gets to about 95 F here in the afternoon. I have always turned it off during the day, but my weak-ass AC takes about an hour to cool 3-4 degrees, so have to run it for a long time after I get home.

 

[Sophia]

I have no idea which one saves more electricity, but perhaps look into programmable thermostats which can turn up the thermostat when you aren't there, and turn it back down a few hours before your return.

 

[FuxOC]

yes i want to know about this too.. my girlfriend swears you save electricity by leaving it on, so it comes on intermittently.. i guess it kinda makes sense but who the hell knows. my electric bill is always over $110/mo in the summer.

 

[Rage187]

nevr shut it off, always have it set at a steady rate IE..I have mine set at 75, if you shut it off, it has to work twice as hard to catch back up and will cost you more money..

If you have a 2 story, close the vents down stairs, and only leave the upstairs vents open, cold air will fall and cool the lower floor..

 

[Boogak]

Yeah, I leave my apartment in the upper 70s when I'm at work, then crank it back down to 70 when I get back. I'm sure my apartment would shoot into the 90s if I left it off. Texas summers suck.

 

[mackstann]

dont do it you will melt and die.

 

[mackstann]

what he ^^^^^ said.

 

[wyvrn]

There was as study by my local elec company sponsored by the city. They did a 2 year study with something like 1000 households participating. The key metric they found for expense what time the AC unit was running. Since most AC units (any?) do not have multiple settings (like the normal and max AC you see in cars nowadays), total time running was the overall factor. Obviously, leaving the unit on constantly at the most comfortable setting is the most expensive. Turning the unit completely off, and then starting it when one got home was next expensive, because (esp. here in TX) the AC would then be required to cool down from 20-30 degrees difference, and this took a long time for most units (time again being key factor). They found the key to maximizing efficiency was to set the AC 10 degrees higher than normal when you left the house, and then turn it back down when you got home. This reduced the time the unit ran during the day, and minimized the time it would take for the AC unit to "catch up" when you got home.

I tested this and found it to be true for myself, both in my apt. and house.

YMMV

 

[MichaelD]

Yep, I agree. I live in South Texas, where it hits 90F by early May. It hit 100F yesterday and will prolly (95% probability) be 100F every day until late September. There is a price to be paid for not having to deal with snow. That price is heat exhaustion.

I live on the second floor of a two-story apt complex. It gets freaking hot in my place. When I'm not home I set the thermostat to 80F and then turn it down to 75 when I'm home. At night I drop it to around 72 or so.

I've tried jacking it up to 85 when I'm not home. No good. The house is a sauna when I get in and takes hours, literally, just to get down to 80F.

There are many things you can do to keep the house cool. During the day, keep all blinds all the way down and tightly closed to keep sunlight out. YOu'd be surprised what a diff this makes.

Also, something we all know; monitor generate a lot of heat. My bedroom, which is already the warmest room in the house, because the roof over the bedroom is lower than the roof over the rest of the house, gets noticeably warmer after the monitor has been on for about an hour. That's why I shut it off during the day.

 

[Yo Ma Ma]

With the correct data one could figure out exactly the point at which it would become cost-effective to turn the AC off or leave on.

It takes the same amount of energy to lower a 90 degree house to 75 whether it's been 90 for an hour or for weeks, I imagine when away for extended time (such as on vacation) it would make sense to raise the thermostat, but on a daily basis it would seem (intuitively speaking only) it might make sense to raise it a few degrees but nothing too drastic.

 

[yellowperil]

For a small apartment I'd wager to leave it off during the day. For a house, it probably would take a lot of energy to re-cool.

 

[Capn]

Depends upon a few factors, amount of insulation in your house, amount of windows and location, size of your house and furnishings inside, ambient air temperature. If you wanted to it wouldn't be that hard to set up a simulation to see which requires more energy.

Just an estimation here though, I think it depends on the size of your house. If you have an extremely large house then maybe keeping it on or partially on during the day would be better than turning it on just when you get home. If you have a small apartment just turn it on when you get home, or program it to turn on a little before you get home.

 

[gooch]

When I was in my apartment (2nd floor, in Phoenix, AZ) we were hit with a $96 electricity bill. This was keeping the thermostat set @ 79. We decided to try turning off the A/C during the day while we were out at work during the week. The resulting bill? $110. Of course, there are always other factors.

Now that we are in the house, we have both thermostats set @ 79 all the time. I have yet to see the bill, but I know it will cost more regardless (2 stories, 3360 sq ft). I only have 10 SEER A/C units, and 12 SEER is regarded as energy star compliant. Maybe when these units go out, I will get 12 SEER units. I will let you know if my bill goes down in 5 - 10 years.

 

[MichaelD]

Sheeeeeet. My electric bill from last month was $110. I have a 710sq/ft, one-bedroom apt. I have a new AC unit. Just replaced in March. I don't know the SEER rating on it though. I'm sure it's not that great a unit because I live in a so-so complex (poor middle class people like me) and they won't spend big bucks on anything. But, it makes the air a heckuva lot colder than before.

Also, I have three snake tanks that have heating pads and lights that are on 24/7. The heating pads all together rate about 100watts, and I have about 200watts of lights on there....so I'm sure that has something to do w/it. Geez, and I live alone too! It's HOT down here in South Texas....we hit 90 in May, no problem. North Dakota and other Northern-teir states still have SNOW in May. I don't miss that crap at all. I'll take the big electric bill over digging the car out 3x a day, anyday.

 

[GrumpyMan]

If you turn off your ac then it supposedly takes longer to cool off the apartment because all the furniture and carpet etc. is hot. If it is kept 10 degrees above normal operating temperature then the furniture does not get hot so the ac does not have to work as hard to get back to say 75 degrees. Or so says my electric company.