Is less electricity used with the air on while away or turning it on when i come in and it runs on to catch up

Question

Is it better to leave on my central air while I'm away, maintaining a constant temperature, or to turn it off the hours I'm out, knowing that when I come home to a hot house it has to run constantly for a much longer interval, at first, to bring the temperature down to the preset comfort level. I quess I'm asking from a conservation standpoint, as in which method is likely to use less electricity--- but also which is likely to be less costly as well, as I am aware that many factors come into play, such as peak hour rates and such. Thank you.

Answer 1

It is better to keep it on just a little warmer than if you were there.  The problem is not just the heat but the moisture in the air. The A/C would work over time just to dry the air first before it could cool your home.

Answer 2

This is simple science.  Heat flows from places of higher temperature to places of lower temperature.  The greater the temperature difference the faster it flows.  It's exactly like water flowing down a hill.

Your air conditioner is pumping heat from inside to outside.  By leaving it off during the day you reduce the temperature difference between outside and inside.  So less heat flows in, and your air conditioner needs to move less heat back out.

But you shouldn't have to come home to a hot house.  Buy a programmable thermostat and have it turn on the air an hour or two before you come home.  You get comfort and save most of the energy anyway.

Answer 3

Something everyone should know about the a/c in ones home.  It does not work like your car, no matter how low you pull the temp. gauge down, it is not going to blow the air out any faster or colder, it will just run longer.  

Now, if you're really looking to save energy...Pick a small room in the house, make it you're cool down room.  Leave the ac off when you're gone, and when you return turn it on-but put it at between 75-78.  Go into your room, close the door and turn on a fan, get a window fan (not a window unit, but one of the fans that fits into a window) and use it to help you cool down while the rest of the house cools.  It will only take about 15-20 mins for your body to cool to the temp of the house, and you should be fine after that..

Or, leave it on all day at 78, and pull it down to about 73-75 the first hour after you get home..Both will have the same effects as far as cost.

Answer 4

Off uses less energy than on.

If you are concerned about humidity you can program a modern thermostat for appx 85 F most of the time you are normally gone and then 78 F when you will be home.

So the place will be comfortable when you get home from work... program the thermostat to go to the comfort temp appx 30 min before you will get there.

There's no real need to cool your house below 78 F  The larger the temperature difference between inside and outside, the more energy you use to maintain the temperature inside.

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Basically the same logic when heating in the winter... let temperature fall to 55 F when the house is empty... and then heat to 72 F when occupied.

Answer 5

It is better to let it get hot while your gone, then let it catch up when you get home.

Better yet, you can purchase a programmable thermostat.  This will automatically raise the temperature while your gone, but have it cool by the time you get home.  You could literally save hundreds per year depending on your cooling system, size, location, etc.

I am a mechanical engineer and have been involved and done testing on concerning this topic.

To prove further, energy codes called IECC (international energy conservation code) is MANDATORY in hot cities like Phoenix, AZ.  Part of these codes is mandatory progammable thermostats as I mentioned above for all newly planned commercial projects.