efficient air conditioner use

Leave Your AC On or Turn It Off?

A common myth about the way air conditioners work may be wasting your money and contributing to global warming.

efficient-air-conditioner-use-thermostatPhotograph By Thinkstock

We've all wondered this at some point, usually after coming home to a stifling house on a long, hot, summer day: Do you save energy by shutting off your air conditioner when you're gone for the day? Or is it better to just let it run at the same temperature setting all day long, so you don't expend extra kilowatts starting it up and getting the premises to a comfortable temperature?

Wasting energy not only costs you more money, it leads to more burning of coal and other fossil fuels that contribute to global climate change. We contacted Jennifer Thorne Amann, MES, buildings program director for the American Council for an Energy-Efficient Economy (ACEEE), to help us figure it out.

THIS: Leave the AC running, set at the same temperature all day.

The theory: If you leave the AC running with the temperature set at a comfortable setting, the stable temp means the air conditioner won't have to work as hard.

THAT: Turn the AC off when you leave; turn it on when you get home.

The theory: If you let the house get hot when you're away, the air conditioner will use more energy when it’s time to cool things down.

THIS OR THAT? That. Turn it off when you leave. It may seem like a waste of energy to turn your air conditioner on and off, but doing so actually saves you a fair amount of money and helps your air conditioner work more efficiently, says Amann. While it may seem like your unit has to work hard to cool a space down from 80 to 75 degrees, "air-conditioning systems run most efficiently when they're running at full speed," rather than running for shorter periods at a less powerful speed to maintain a constant temperature all day, Amman says. They're also better able to dehumidify your house, she adds, when they run full blast.

More From Rodale News: 10 Budget-Friendly Ways to Keep Your House Cool This Summer

If you have central air, or a window unit with a thermostat, you can save energy and keep things from getting unbearably torrid by setting the thermostat higher. ACEEE estimates that air conditioners use 3 to 5 percent less energy for every degree you raise the thermostat. To get the best energy savings, leave your thermostat set at 78 degrees or higher while you're out.

Here are a few other ways to stay cool and get better AC energy savings this summer:
• Buy a programmable thermostat. Whether you turn your central air off or turn its thermostat up when you're out of the house, a programmable thermostat can crank up the cool factor before you get home. That way your house will be comfortable when you walk in the door. Amann notes that you’ll need to buy a thermostat that suits both your cooling and your heating systems. Some models don't work with heat pumps, which can pose a problem in the winter, so check with whoever installed or services your system. If you use a window unit, an appliance timer can serve a similar purpose; newer models may include a timer as well as a thermostat.

• Buy a ceiling fan. Fans don't necessarily cool a room, but they move air across your skin, making you feel comfortable at a higher temperature. That allows you to set the thermostat higher and stay cool while using less energy (especially if you buy a fan that's Energy Star rated). However, because it doesn't reduce the temperature of a room, it's a waste of energy to leave a ceiling fan on in the hopes that it will keep your house cooler while you're gone.

More From Rodale News: The Energy-Saving Trick That's Costing You Your Health

• Plant some bushes. Large, shady bushes or trees planted on the south and west sides of your house will reduce heat gain during the day. (Be sure to choose native plants.)

• Create crosswinds. The easiest way to cool a house? Open a window—but not too much. The less you open it, the more of a draft you'll create. You can create cross breezes in a one-story house (or a single room) by cracking one window's bottom sash and another's top sash. If you live in a two-story house, open a window on the first floor a crack and another window upstairs on the opposite side of the house. Experiment to see which windows work best and how much you should open them.


Published on: June 16, 2009

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The best option I feel is to

The best option I feel is to make AC run in a fixed temperature where it doesn't burn much power in every turn off and on.

Mold Removal Montreal If you

Mold Removal Montreal
If you are going to leave your house for a short while, it is still better to leave the AC on instead of shutting it down. One perk of dehumidifying the air is that it might help prevent the growth of mold. However, the cost savings are what most people would be more concerned about.

I am a manager at a hotel,

I am a manager at a hotel, and we use PTACs for all our individual rooms. We never shut the air off completely because it causes more energy to turn it off than to just leave it running. The key is to set it at a higher temperature when there is no one staying that particular room, and then turn down the AC when it's time. That way the room is already cooled off, it just needs a little more air to cool off a little bit more, which saves money.

Thanks for posting this

Thanks for posting this piece. Great ideas - i love this! I'm tired of reading about Swine Flu!!!! Maybe these ideas actually will make my kids healthier too??!
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I think that it is a waste of

I think that it is a waste of money if you leave your AC on while you don't stay inside the house.I believe that an AC can make a difference very faste in a room and it is not worth it to let it work when you are not in the house.I just bought a new house and I have to install an AC system beside the fact that I have to check up sleep number bed costs because I don't really like the ones which came with the house.

Sometimes if you want to get

Sometimes if you want to get cooler and you don't want an air conditioner, well, you can use a double vanity in the summer. Water is a natural method for staying cool. I hope you find my suggestion useful. Good luck!!

Air conditioning

Well I was told a long time ago about how turning on and off is better for the health of your wallet and does not use up the machine or lights or actually your air-conditioner in any way think about it if you leave the fan on there will be new air and in any case if you turn it all off it does not take long for the room to become comfortable again. I think it is simple and if you can program it simpler.

Great article! I think this debate also reminds

Great article! I think this debate also reminds me about the debate about whether to leave lights on when you leave the room or turn to turn it off when you leave. With current technology, I think it is more energy efficient if we turn off appliances that we are currently not using. Leaving the air-con temperature slightly higher but using the fan for air circulation is a great tip. Wish I could do the same for my CPAP machines.


The discuss in the office never stops in this regard. Programmable thermostats are the best maybe. Get one. Testking 156-215.71 There are some who can operate outside internet.But some people do not see it, no matter what is said Yuya, or what evidence you have, they will decide what they want. Testking 000-118 I say just turn the sucker out.

Air conditioning

After reading DNR and other website's articles on energy efficiency, I've started leaving my AC on 84 when I'm away, and I also find, when I come in from an outdoor temp of 90 or so, even at an 81 degree setting on the thermostat, I'm comfortably cool. So that's what I keep it on, occasionally bumping it down to 80, when I'm home. I live in the South, so I'm kind of used to hot weather. I also realize I'm so lucky to afford air-conditioning and feel guilty about being too "wimpy", when I think about the many people in really hot climates who just have to tough it out because they aren't so lucky. At work, I've about given up--these guys in their coats and ties are not going to turn up the thermostat. Heaven forbid that they should change their male dress code to dress more sensibly for hot weather! Instead, I have to wear a sweater sometimes when it's 100 outside to keep from freezing in my office! NL

Air Conditioning, On or Off?

The debate around the office never stops on this. Programable thermostats are the best probably. Get one. There are some that can be operated off the internet.But some people don't believe you no matter what youi say, or what evidence you have, they are going to believe what they want. I say just turns the sucker off. That's the simplest thing.

What's the best temperature to keep the air conditioner going?

Wasting energy by using the air conditioner? I know I have an economic option on mine, I still haven't figured what's the optimum temperature to keep the AC going in an effective way but also for saving energy. So keeping the AC on all day is more cost effective?

air on or off

Is it more efficent to leave window air on or turn off when leaving?

Central 'FAN'

Our unit not only has central 'AIR', but also a central 'FAN'.
The question...(fight) is it better to turn the fan on, & allow the (warm air, if you will)circulate; or is it better left off (& stagnate)?

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