Does my electric bill go up if the a/c is turned off and on?

If I turn my central A/C off and leave for the day, and turn it back on when I get home, does that increase wattage and $$? Or would it be cheaper to just leave it on? I have a two bedroom condo.

Does my electric bill go up if the a/c is turned off and on?
In spite of all the complicated reasoning one way or the other in the other answers, there is a basic physical law that is inviolate: the Conservation of Energy. In your situation, it means that the more energy in the form of heat that you remove from your condo, the more energy in the form of electricity is consumed by the air conditioner.





Shutting the air conditioning off during the day will save electricity. When you get home, though, the air conditioner will have to run a while longer to get the temperature back down to a comfortable range. For this reason you might want a programmable thermostat that will turn on the air an hour before you get home. In either case you'll save electricity compared to leaving the air running all day long.
Reply:In high humidity days it is best to leave on. If you don't have a programmable thermostat this is the time to buy one at Home Depot or Lowes.





Program the AC to allow a higher temperature, maybe 5 degrees warmer, when you are away. Then program to lower the temp an hour before you get home. If the AC is off all day then the interior of you home will absorb moisture. This includes everything inside the home.





So, the trick is to keep the humidity as stable (and low) as possible during the summer months. The main function of an AC is to lower Humidity and not to merely cool the air.
Reply:Facts affecting Air Conditioning (AC) Power Use


· Heat loss or gain is directly proportional to the square of the difference in temperature on two sides of the material be it a wall or window


· So, if the temperature difference is 20 degrees, say 72 inside and 92 outside, it will transfer 4 times as much heat compared to a 10 degree temperature difference.


· If you turn off the AC or set the thermostat to a higher temperature, the temperature difference will be reduced saving power, fuel and money.


· The down side to this approach is that when you come home and the house is hot, it will take a while for the AC to catch up and you may be uncomfortable during that time.


· A fix to the wait for the AC to cool things off is a programmable thermostat, available at home centers, that will raise the set point and then lower it again at times you program in so it can increase the temp soon after you leave for work and bring it back down say a half hour before you normally get home.


· Take into consideration pets, plants and other things that may be sensitive to high temperatures. 78 degrees should not hurt anything though.
Reply:In a two-bedroom condo, its better just to set the thermostat back a bit when you are not there. If you live in a high humidity area, turning your air all the way off will encourage mold and mildew in your carpets and bathroom. In a large house the airconditioner would have to run for a long time without shutting off to cool a house down after being off all day on a hot day, to the point where it might wind up costing more.
Reply:bill goes up when its on, bill stays the same when off....whats to figure? all these theories about leaving it on all day are worthless... been doing this for over 30 years...just keep your shades and windows shut when out
Reply:The issue you are fighting is the thermal mass.. If you turn it off and you live in a hot area, the ac has to work harder and longer to cool everything back down so you spend more money and more wear and tear.


If you live in a more temperate climate, turning it off is not as big an issue.


The best thing to do (and this requires some experimentation on your part) is to get a programmable thermostat and have it cut the cooling back to let it get say 5-7 degrees warmer than you like during the day and then have it kick back up about 30 mins before you get home in the evening.





The key is finding the right mix and that will be specific to your coolness desire, the house insulation and the region you live in.


Note this can be done with heating in the winter and works well if done at night while you are snuggled in the blankets.. have the heat drop 30 mins after bed time and ramp up 30 mins before time to get up..

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