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  1. #1
    Join Date
    Nov 2007
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    73

    Default Leaving the A/C on all night?

    I am wondering which is more cost efficient. I want to turn the ac on during the day, only when needed. At night, I like to open the windows and get a nice cool breeze (if there is one) Hubby wants the ac on 24/7. His argument is that the unit works less when it's on all the time and the windows stay closed.

    I keep the ac set to 78 degrees during the day. Opening the windows means the house will cool down to 72 or so even on a warm night. Keeping the windows closed will only cool the house down to 77 (or so it has been the last few evenings) unless we turn the ac down and have it run all night long to cool the house.

    We are using a standard ac unit in a 1,400 sf(aprox) house. Although the ac has the ability to dehumidify, there is little to no water draining through the unit. We live in Colorado where it is already dry, and I purposely turn the humidifier on the heater/ac unit up so we have more humidity in the house. (even then it's not much)

    So the question is: Is it better to run the ac all night? or better to give it a rest and open the windows? Which one would save the most money?

  2. #2
    Join Date
    Jul 2010
    Location
    SoCal
    Posts
    7,762

    Default Re: Leaving the A/C on all night?

    There are no simple answers to your questions. Why? because there are a few factors to consider.

    Why don't you run a test to determine which method uses more power? On day 1, disconnect all power users, including the fridge, and see if your meter indicator is at standing still, just to check.
    1. If it is, then start the test by recording the meter reading and the time. Now, connect the fridge only and don't use any other power consumer for 24 hours, except the a/c when you want it. Read the meter.
    2. The next day, turn all users off, but leave the a/c and fridge on all night and all day and after 24 hour read te meter.
    3. Is there a difference? I thought so.
    4. Beating your unit to death will result in the unit quitting prematurely. More money down the drain.

    "Cooling" is a relative concept. If the outside temp is 95 and the inside temp is 88, then it feels warm. But to save power and money, don't lower it to 72-78, because if you lower it to 84-85, you will FEEL about the same, for less money.

    I have tenants who want to live in 74 while it's 104 outside. They will always be tenants.

    Right now I have a tenant who called me on Jul 3rd to complain about a broken a/c. Well I told her that she drove the unit to the ground, and now she is expected to be without a/c a few days, until a service man can come and test it. My a/c guy is booked until later during the week. If she wants a quicker repair (that she might find for triple the money), she is on her own.

  3. #3
    Join Date
    Aug 2007
    Location
    Maryland
    Posts
    2,009

    Default Re: Leaving the A/C on all night?

    Personally if the temps cool down at night to below what I set the a/c at which is 76 i will open the windows especially if the humidity isn't too bad. I suspect humidity is more an issue near baltimore than in Colorado.
    I will often leave the a/c on, but since the outside is cool it usually won't come on until the next day when it heats up. Then I will close the windows again.
    If the weather is marginal with heat and humidity I may leave it on, but crack the window in the bedroom at night and close it in the morning.
    I like a bit of fresh air when possible. Even with closing the windows when the a/c comes back on, I realize I'm spending a little extra money removing moisture from the air.
    I would say if the humidity is low and the temps really cool off at night, you would save money opening the windows. Besides you would miss the birds chirping at the crack of dawn if the windows were closed.

  4. #4
    Join Date
    Aug 2007
    Posts
    8,046

    Default Re: Leaving the A/C on all night?

    Quote Originally Posted by Capellam44 View Post
    I am wondering which is more cost efficient. I want to turn the ac on during the day, only when needed. At night, I like to open the windows and get a nice cool breeze (if there is one) Hubby wants the ac on 24/7. His argument is that the unit works less when it's on all the time and the windows stay closed.

    I keep the ac set to 78 degrees during the day. Opening the windows means the house will cool down to 72 or so even on a warm night. Keeping the windows closed will only cool the house down to 77 (or so it has been the last few evenings) unless we turn the ac down and have it run all night long to cool the house.
    If the thermostat is set at 78, then the unit will only run when the indoor temp is above that temperature. Opening windows at night to let cooler than 78* night air in will actually save you money, because the unit is not coming on to continue cooling a hot house over night, you're doing it with natural air flow. Additionally, with cooler indoor temps the next day, the unit has to run less to maintain the 78* setting.

    This is the method we use as well, thermostat at 80*, open the house up as soon as the outside air temp is lower than inside air temp, then use box fans to circulate air throughout the house.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  5. #5
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    2,016

    Default Re: Leaving the A/C on all night?

    In your area. I have to agree with you. You don't have high humidity, your nighttime temperatures are cool and not having to listen to the AC running all night is a real bonus.

    Now if you lived in my neck of the woods, you would be wrong. High humidity and high nighttime temperatures in the summer means the AC has to run 24/7. Around here, if you have a programmable thermostat, it is a good idea to program a lower temperature sometime before dawn when the outside temperatures at their lowest and the AC runs more efficiently to get a running start on the day.

  6. #6
    Join Date
    Nov 2007
    Posts
    73

    Default Re: Leaving the A/C on all night?

    Thanks guys. I guess hubby will have to let me leave the windows open. Besides, I love the fresh air, and it does cool the house down more than the a/c would, unless we lowered the temp down and sucked up more juice, and put more wear and tear on the unit.

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