Anonymous asked in EnvironmentGreen Living · 1 decade ago

Which uses more energy, constant airconditioning, or shutting it off for about 4 hours?

i've had people tell me that it costs more to cool down the house after i turn off the air conditioning.

is that true?

my attitude is that i should turn it off when i leave the house; about 9 hours or so while i'm at work.

also i have been told that turning it on and off will cause eventual damage to the unit.


7 Answers

  • 1 decade ago
    Best Answer

    You'll save a LOT of energy and money by turning off the A/C when you go to work.

    I don't know where those people that told you otherwise got their ideas. Maybe they're just rationalizing, because they don't like to come home to a warm house.

    But don't just trust me. Take a look at your electric meter in the morning when you leave, say, at 7 am. Write down the number. Leave your A/C on for the day, and the next morning, note the electric reading and see how many kWh's were used. On some other comparably hot day, try my plan of turning off the A/C, and measure how much energy is used.

    It was once true (the 1970's and earlier) that starting the air conditioner's compressor on and off repeatedly in a short period of time was stressful to it. There was a caution in the owner's manual. Modern air conditioners don't have this concern - look in your owner's manual, and you won't see the warning. And even in the 70's, the problem was if you turned the A/C on and off every 15 minutes, not if you turned it off for 9 hours while away. Moreover, the compressor cycles on and off during normal operation anyway.

  • When you turn off the air conditioning, your rooms start absorbing heat from the outside. How fast they absorb it affects how long the air conditioner will have to run afterwords to bring the room temperature back down to where you had it set. People use this argument to suggest that you'll use less energy if you keep running the air conditioner all the time. But this is wrong and it's easy to understand why.

    When the air conditioner is running the temperature difference between indoor and outdoor air is greater. Therefore, more heat leaks through from the outside to the inside.

    When the air conditioner is off, the temperatures slowly come into balance as the inside warms up due to the heat flowing in through walls. The warmer it gets inside, the less heat energy enters the house.

    Of course it takes more energy, from 5pm to 6pm, to cool a room down than to keep the room cool if it was already cooled from 12pm to 5pm. But in the second scenario you didn't use any energy keeping it cool from 12 to 5, so you wind up saving a lot.

    This is why the US DOE recommends that everyone use a programmable thermostat for both air conditioning and heating - the more often you can minimize or eliminate your use of air conditioning or heating, the less energy you'll use overall.

    For the length of time you are suggesting - 9 hours - you are definitely better off turning off the unit, and you will not cause any damage to it. The way you damage a unit is by rapid cycling - which can happen when the unit is on and not functioning properly, for instance with an oversized unit, when there's poor circulation around the coils, or low refrigerant levels. It can also happen when you turn the unit on and off repeatedly, say once every 15 minutes. But if you keep it to less than once an hour there'll be no negative impacts.

    It also saves more energy to only cool the rooms you need cooled, and to raise the temperature you cool them to. Also make sure you open the windows and draw in cool night air if the temperature outside gets lower than that indoors. I often see people running their AC in the evening or overnight when I'm out walking in my fleecy and long pants - just doesn't make sense.

  • Anonymous
    1 decade ago

    In Arizona you never have to ask this question. I keep my air temperature at 87 degrees and keep it on all the time. Since I have been doing this I cut my electric bill in 1/2. It takes more electricity to cool down a house. If the outside temperature is say, 100 degrees, you can bet the inside temperature is a lot more. I keep fans blowing when I am in the house and it takes the inside temperature down about 5 to 7 degrees. Also keep your drapes or curtains closed during the daytime and it will help. Is there a window on any of your outside doors? If so, tack up a towel temporarily until you can make a curtain for it. For more help, search for a weatherizing question here.

  • ?
    Lv 4
    1 decade ago

    I lived in Louisiana. I had an 18,000 BTU window unit in the living room that could cool the room from 90 to 70 in about ten minutes. If I left to go to work. We would shut it off. It is cheaper not to run it. But a marginally sized unit will take along time to cool the room back down. During this period the compressor will run constantly, and it may cost more. Bottom line is that if the room cools down in a hurry, then it is cheaper to shut it off. If it takes along time to cool it down, then it is cheaper to leave it on.

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  • 1 decade ago

    I think leaving air on is better. You need to make sure all your

    doors and windows are well insulated. I even put a towel under the

    door in my kitchen the preserve the cool air. It's going to be 95 degrees today in my hometown and I want to do all I can to reduce

    my electric bill and not waste

  • jon
    Lv 6
    1 decade ago

    when the outside temp is 70 or below,the humidity is low ,I turn it off .I don't have to but that's the way the wife wants it. When it is hot humid we never shut it down. we do turn up the temp more so we won't freeze to death when we come in

  • Anonymous
    1 decade ago

    well, obviously turning off the unit will use less energy, but you may want to reconsider turning it off completely and just turn the temperature up. This way you can keep your home dehumidified and eliminate any chances of condensation problems.

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